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Organs of the endocrine system: Anatomy and functions

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Last reviewed: November 12, 2020

Reading time: 29 minutes

The endocrine system is a collection of glands. These glands secrete a variety of hormones, which travel to specific target organs via the bloodstream. Hormones have specific functions such as regulating growth, metabolism, temperature and reproductive development. Like the nervous system, the endocrine system acts as a signaling pathway, although hormones are slower acting than nerve impulses.

Endocrine signals can last from a few hours to a few weeks. The main control center for the organs in the endocrine system is the hypothalamus in the brain. The field of medicine concerned with the endocrine system is known as endocrinology.










Key facts about the endocrine organs
Hypothalamus
Borders: anteriorly – anterior commissure, lamina terminalis, optic chiasm; posteroinferiorly – posterior perforated substance; inferiorly – infundibular stalk; superiorly – hypothalamic sulcus and the base of the third ventricle
Structure: chiasmatic region, tuberal region, mammillary bodies
Function: produces releasing and inhibiting hormones that affect the pituitary gland
Hormones: anti-diuretic (ADH), corticotropin-releasing (CRH), gonadotropin-releasing (GnRH), growth hormone-releasing and -inhibiting (GHRH and GHIH), oxytocine, prolactine-releasing and -inhibiting (PRH and PIH), thyrotropine-releasing (TRH)
Hypophysis
Location: pituitary fossa, connected to hypothalamus via infundibulum
Structure: adenohypophysis, neurohypophysis
Function: produces stimulating-hormones that affect endocrine glands of the body
Hormones of adenohypophysis: human-growth hormone (hGH), thyroid-stimulating (TSH), follicle-stimulating (FSH), luteinizing (LH), prolactin (PRL), adenocorticotropic (ACTH), melanocyte-stimulating (MSH)
Hormones of neurohypophysis: oxytocin, antidiuretic hormone (ADH)

 
Pineal gland
Location: between superior colliculi
Function: regulates sleep-wake cycle
Hormone: melatonin
Thyroid gland
Location: anterior surface of neck at levels C5-T1
Structure: left lobe, right lobe, isthmus (connects the lobes)
Function: regulates metabolysm (by enhancing it)
Hormones: thyroxine (T4), triiodthyronine (T3), calcitonine
Parathyroid glands
Location: posteriorly to the lobes of thyroid gland
Function: regulates blood levels of calcium (by increasing it)
Hormone: parathyroid hormone
Endocrine pancreas and gastric mucosa
Location: Langerhans islets of the pancreatic tissue, gastric mucosa
Function: regulates blood levels of glucose, regulates digestion
Hormones: insulin, glucagone, gastrin, secretin, ghrelin, motilin, cholecystokinine, gastric inhibitory polypeptide
Adrenal glands
Location: superior poles of kidneys
Structure: adrenal cortex (secretes glucocorticoids and mineralocorticoids), adrenal medulla (secretes biogene amines)
Function: regulates blood pressure, electrolyte balance, stress response
Hormones: glucocorticoids – cortisol, corticosterone; mineralocorticoid – aldosteron; biogene amines – epinephrine, norepinephrine, dopamine
Gonads
Function: regulates sexual development, behaviour and characteristics; regulates gametogenesis
Hormones of testes: testosterone
Hormones of ovaries: estrogen, progesterone
Clinical relations Hyperfunction, hypofunction, adenoma, carcinoma

This article will discuss all of the important anatomical and functional aspects of endocrine system.

Organs of the endocrine system

Endocrine glands tend to be vascular and do not have ducts. Ducts are instead found in exocrine glands, which produce hormonal signals outside of the body. The hormones of endocrine glands are stored in vacuoles or granules, ready to be released.

Endocrine glands are found throughout the body and have a variety of different roles. The key endocrine glands and organs are listed below:

  • Hypothalamus
  • Pineal gland
  • Pituitary gland
  • Thyroid gland
  • Parathyroid gland
  • Ovaries
  • Testes
  • Pancreas
  • Adrenal glands
  • Gastrointestinal tract

Hypothalamus

Borders

The hypothalamus is an almond-sized structure in the limbic system of the brain, and the endocrine system’s control center. Its borders are the following:


  • Anteriorly: anterior commissure, lamina terminalis, and optic chiasm

  • Posteroinferiorly: the posterior perforated substance

  • Inferiorly: the infundibular stalk

  • Superiorly: the hypothalamic sulcus and the base of the third ventricle

Structure

Anteroposteriorly, the hypothalamus can be divided into three regions: chiasmatic, tuberal and the region of the mammillary bodies. The chiasmatic region lies immediately above the optic chiasm (hence its name) and is related with the circadian rhythm and the variations of the endocrine secretion throughout the day. The tuberal zone contains the tuber cinereum. This mass of grey matter is located between the mammillary bodies and the optic chiasma. The infundibulum projects from the tuber cinereum, becoming continuous with the posterior lobe of the pituitary gland. A structure called the median eminence is separated from the base of the infundibulum by a tuberoinfundibular sulcus. And finally the region of the mammillary bodies, which are hemispheral and pea sized structures situated anteriorly to the posterior perforated substance. Their role is to control memory and emotional expression.  

Mediolaterally, the hypothalamus can be divided again into three zones: periventricular, intermediate and, lateral. The regions and zones contain and border several hypothalamic nuclei, each one being responsible for particular functions.

Function

The hypothalamus controls the endocrine system via several pathways. These include direct projections to the posterior pituitary (neurohypophysis), and indirect control over the anterior pituitary (adenohypophysis) via projections to the median eminence and via the autonomic nervous system. The hypothalamus carries out its control by producing releasing or inhibiting hormones, known as neurohormones. Releasing hormones stimulate the production of hormones in the pituitary gland, whilst inhibiting hormones inhibit it.

The neurohormones produced by the hypothalamus to manipulate hormone production by the pituitary gland include:


  • Anti-diuretic hormone (ADH): This increases water absorption in the kidneys.

  • Corticotropin-releasing hormone (CRH): This stimulates the release of corticosteroids by the adrenal glands, regulating metabolism and immune response.  

  • Gonadotropin-releasing hormone (GnRH): GnRH stimulates the production of follicle stimulating hormone (FSH) and luteinizing hormone (LH), which combine to maintain ovary and testes functioning.

  • Growth hormone-releasing hormone (GHRH) or growth hormone-inhibiting hormone (GHIH): GHRH prompts the release of growth hormone (GH), whilst GHIH has the opposite effect. In children, GH is essential to maintaining a healthy body composition. In adults, it ensures healthy bone and muscle mass and is involved in fat distribution.

  • Oxytocin: This is involved in the release of breast milk, orgasm, and smooth muscle contraction. It also regulates body temperature by helping to redistribute heat, and sleep cycles as increasing levels of oxytocin are thought to help induce sleep.

  • Prolactin-releasing hormone (PRH) or prolactin-inhibiting hormone (PIH): PRH stimulates the production of breast milk, whilst PIH inhibits it. This can also be seen in males too, although it is a sign of significant health issues.

  • Thyrotropin releasing hormone (TRH): TRH triggers the release of thyroid stimulating hormone (TSH), causing the release of thyroid hormones which regulate metabolism, energy, growth, and development.

Pituitary gland

Location

The pituitary gland (hypophysis cerebri) is a pea-sized, ovoid shaped structure attached via the infundibulum to the tuber cinereum of hypothalamus. It is located within the pituitary fossa (sella turcica) of the sphenoid bone. The diaphragma sellae of the dura mater only partially encloses the gland within the fossa because it contains an aperture for the infundibulum. A venous sinus separates the gland from floor of the fossa.

Structure

The pituitary gland has two main parts: neurohypophysis and adenohypophysis. The neurohypophysis is an actual downgrowth of the diencephalon directly connected to the hypothalamus. Both parts include the infundibulum. The neurohypophysis incorporates the stem of the infundibulum, which is a continuation of the median eminence of the tuber cinereum. It also contains the posterior (neural) lobe. The adenohypophysis can be separated into the pars intermedia (the boundary between the two pituitary lobes) and the pars anterior (anterior lobe), both forming a part of the adenohypophysis. The adenohypophysis also contains the pars tuberalis, a vascularized sheath surrounding the stem of the infundibulum.

The main neurosecretory pathway through the neurohypophysis originates from the supraoptic and paraventricular nuclei of the hypothalamus and terminates near the sinusoids of the posterior lobe. As a result, hormones are released directly in the circulation. Another group of neurons that end in the median eminence and infundibular stem release the inhibitory and releasing hormones within the hypophyseal portal system, ultimately controlling the secretory activity of the adenohypophysis.

Function

The pituitary gland stores some of the hormones that the hypothalamus produces, before releasing them into the blood. Out of the two lobes, the anterior lobe is larger, making up 75% of the gland. It also has a larger role in the release of hormones, although the posterior lobe still does some work.

The anterior lobe secretes a total of 7 different hormones into the bloodstream, which are as follows:


  • Human-growth hormone (hGH): hGH stimulates tissue growth and protein synthesis for tissue repair.

  • Thyroid-stimulating hormone (TSH): TSH causes hormone production by the thyroid gland.

  • Follicle-stimulating hormone (FSH): This causes estrogen production in females, as well as the development of oocytes (immature egg cells). FSH also stimulates sperm production in the testes .

  • Luteinizing hormone (LH): LH stimulates estrogen and progesterone production in females, and testosterone production in males.

  • Prolactin (PRL): This stimulates milk production in the mammary glands.

  • Adrenocorticotropic hormone (ACTH): This is involved in the body’s stress response and causes the production of cortisol in the adrenal cortex.

  • Melanocyte-stimulating hormone (MSH): MSH can cause darkening of the skin. It may also be involved in brain activity but its exact role in this is still unknown. The pars intermedia manufactures MSH during fetal development.

Meanwhile, the posterior lobe of the pituitary gland is only involved in the release of two hormones; oxytocin and antidiuretic hormone (ADH). Oxytocin is involved in childbirth, milk production, and orgasm. ADH is important in reducing water loss by decreasing urination and sweating, therefore increasing blood pressure.  

Pineal gland

Location

Along with the hypothalamus and pituitary gland, the pineal gland (epiphysis cerebri) is found in the brain. It is a small organ located in a depression between the superior colliculi, inferiorly to the splenium of the corpus callosum. The gland is enclosed within the lower layer of tela choroidea of the third ventricle.

Structure

The pineal gland has a base that is directed anteriorly and is divided into a superior and inferior laminae by the pineal stalk, which also serves as a point of attachment to the roof of the third ventricle. The laminae contain the posterior and habenular commissures, respectively.

The gland parenchyma is highly vascularized and divided into lobules by several septa, which also carry blood vessels and sympathetic nerves. These adrenergic sympathetic axons originate from the tentorium cerebelli and enter the gland as the nervus conarii. The pineal gland parenchyma consists mainly of pinealocytes. The pineal stalk consists mostly of glia.

Function

The pineal gland has a more specific function, being involved only in the secretion of the hormone melatonin. It is released from bulbous expansions of the cell bodies of pinealocytes. This hormone is involved in both sexual development and the sleep-wake cycle. In terms of reproductive development, melatonin blocks the secretion of gonadotropins (FSH and LH) from the pituitary glands.

Melatonin also regulates the sleep-wake cycle by reacting to the amount of light hitting the retina. The retina relays this information to the hypothalamus, which in turn sends information to the pineal gland. The pineal gland secretes melatonin depending on the amount of light hitting the retina. The less light there is, the more melatonin is produced, inducing sleep.

Thyroid gland

Location

The thyroid and parathyroid glands are endocrine glands at the base of the neck. The thyroid gland is the largest gland of the endocrine system. It is located in the anterior portion of the neck at the level of the C5-T1 vertebrae, deep to the sternothyroid and sternohyoid muscles.

Structure

It consists of two lobes, right and left, which ascend upwards to the thyroid cartilage, joined together by an isthmus. The lobes are anterolaterally in relation to the larynx and trachea, while the isthmus is anterior to the second and third tracheal rings. In some individuals, a conical pyramidal lobe ascends from the isthmus towards the hyoid bone.

The thyroid gland is enclosed inside a fibrous capsule, which is attached to the cricoid cartilage and tracheal rings by dense connective tissue. The fibrous capsule itself is enclosed in a loose sheath of fascia. The gland is highly vascularised. The arteries supplying it are the superior and inferior thyroid arteries, which lie between the fibrous capsule and the sheath of fascia. Venous drainage of the gland is via the superior, middle and inferior pairs of thyroid veins, which form the thyroid plexus of veins. Innervation is from the cervical sympathetic ganglia, as well as parasympathetic fibers from the vagus nerves.

Function

The thyroid gland is important in regulating metabolism. It produces 2 important metabolic hormones, thyroxine (T4) and triiodothyronine (T3). T4 contains 4 iodine atoms, whilst T3 contains 3 iodine atoms. T3 and T4 both affect the body’s metabolism by influencing protein production of every cell in the body. This protein production in turn affects tissue growth, temperature, energy use, and heart rate. The thyroid gland also produces calcitonin, which is an antagonist to parathyroid hormone.

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Parathyroid glands

Location and characteristics

The parathyroid glands (usually 4 in total) are small, flattened, and oval structures located on the posterior surface of each lobe of the thyroid gland. They normally lie between the fibrous capsule of the thyroid gland and its external fascial sheath.

The glands are separated into two superior and two inferior ones. The location of the superior parathyroid glands is quite constant, at the level of the inferior border of the cricoid cartilage, 1 cm superior to the entry point of the inferior thyroid arteries into the thyroid gland. The inferior parathyroid glands are usually situated near the inferior poles of the thyroid gland but have a more varied location.

Arteries supplying the parathyroid glands branch from the inferior thyroid arteries. Venous drainage is via parathyroid veins which subsequently drain into the thyroid venous plexus. Innervation is from the parasympathetic fibers from the vagus nerves, similar to the thyroid gland.  

Function

The parathyroid glands maintain calcium levels in the blood by producing parathyroid hormone. Together with calcitonin, these two hormones maintain the level of calcium ions in the blood, which is important in bone health, as well as muscle and nervous system function.

Enteric endocrine system

The gastrointestinal tract itself can produce hormones and is known as the enteric endocrine system. Hormone secreting cells are dispersed throughout the lining of the stomach and small intestine. These cells do not produce hormones continuously, instead they do so in response to the environment inside the stomach and intestine, reacting to the amount of food moving through.

Pancreas

The pancreas is particularly important in the enteric endocrine system, as it releases the hormones insulin and glucagon, which regulate blood sugar levels. The pancreas is an accessory digestive gland. It crosses the bodies of the L1 and L2 vertebrae transversely. The pancreas is situated anteriorly to the stomach and between the duodenum on the right and the spleen on the left. Its anterior margin is in contact with the transverse mesocolon.

This gland has four parts: a head, neck, body, and tail.


  • The head is attached to the descending and horizontal parts of the duodenum, embracing it in a C-shaped fashion. The uncinate process is an inferior projection from the head, which extends posterior to the superior mesenteric artery (SMA).
  • The short neck of the pancreas is covered by peritoneum and is located adjacent to the pylorus of the stomach. The hepatic portal vein is formed posterior to it, by the joining of the splenic vein and the superior mesenteric vein (SMV).
  • The body of the pancreas continues transversely from the neck, passing anteriorly to the aorta and L2 vertebra and posterior to the omental bursa. The anterior surface is covered by peritoneum and also forms part of the stomach bed.
  • The tail is situated anterior to the left kidney and it is an intraperitoneal structure. It is closely related to the hilum of the spleen and the left colic flexure.

Running from the tail to the head, through the parenchyma, is the main pancreatic duct. It joins the common bile duct, just outside the duodenum, forming the short hepatopancreatic ampulla (ampulla of Vater). This structure opens into the descending part of the duodenum. The hepatopancreatic sphincter (sphincter of Oddi) prevents the reflux of duodenal content into the ampulla. The main pancreatic duct also contains a sphincter that controls the flow inside it.

The blood supply is via pancreatic arteries, which branch off several vessels located nearby. Venous drainage is via pancreatic veins and most of these empty in the splenic vein. Innervation of the pancreas is from the vagus and abdominopelvic splanchnic nerves.  

Function

There are six key gastrointestinal hormones:


  • Gastrin: This is stimulated by the presence of peptides and amino acids in the gastric lumen, and is important in the secretion of gastric acid.

  • Secretin: This is produced in response to acidic pH levels, and causes the production of water and bicarbonate from the pancreas and bile duct to help increase pH again.

  • Ghrelin: Ghrelin stimulates appetite and feeding.

  • Motilin: Motilin is involved in movement and contractions of the gastrointestinal tract.

  • Cholecystokinin: This stimulates the secretion of pancreatic enzymes and emptying of the gallbladder in response to an increase in fatty acids and amino acids in the small intestine.

  • Gastric inhibitory polypeptide: This prevents gastric movement and secretions, and causes the release of insulin in response to an increase in glucose and fat in the small intestine.

Suprarenal (adrenal) glands

Location

The adrenal (suprarenal) glands are two triangular shaped glands found on top of the kidneys. They have a yellowish appearance and are located between the superomedial aspects of the kidneys and the diaphragm. The glands are surrounded by renal fascia, which also provide an attachment point to the crura of the diaphragm. A septum separates the glands from the kidneys. The two glands are not identical. The right one is more pyramidal and apical, while the left one is more crescent-shaped. They also have slightly different positions and relations. Veins and lymphatic vessels enter and leave each gland via the hilum.

The blood supply to the adrenal glands is via superior, middle, and inferior suprarenal arteries. Venous drainage is via the right and left suprarenal veins, which subsequently drain into the inferior vena cava and left renal vein, respectively. Innervation is from the celiac plexus and abdominopelvic splanchnic nerves.

Structure and function

The glands are divided into two parts; the adrenal cortex and the adrenal medulla. The adrenal cortex is the outer part of an adrenal gland, and produces hormones vital to life such as glucocorticoids – the horomes hydrocortisone (cortisol), and corticosterone. Hydrocortisone regulates energy production, blood pressure, and heart function. Corticosterone plays a role in immune responses and reduction in inflammation. The adrenal cortex also produces aldosterone, which controls blood pressure.

The adrenal medulla is the inner portion of the gland. It is actually a mass of nervous tissue containing many capillaries and sinusoids. The medulla produces hormones such as adrenaline. The adrenal medulla helps the body deal with stress by producing two hormones, epinephrine and norepinephrine. Epinephrine is more commonly known as adrenaline and is involved in the body’s fight or flight response, increasing heart rate and blood glucose levels, and causing an increase in blood flow to the brain and muscles. Norepinephrine works with adrenaline, by constricting blood vessels and increasing blood pressure during the stress response.

Reproductive

Testes

The endocrine organs in the reproductive systems are the ovaries and testes, in females and males respectively. The testes are paired ovoid glands that produce spermatozoa and the male hormones, mainly testosterone. Each testis is suspended in the scrotum by its own spermatic cord, the left one hanging more inferiorly than the right one, mostly due to the length of the spermatic cord. The testes are almost completely covered by the visceral layer of the tunica vaginalis, a closed peritoneal sac. A recess in the tunica vaginalis represents the sinus of the epididymis. The tunica vaginalis also has a parietal layer, which is adjacent to the internal spermatic fascia. A fluid filled cavity is located between the visceral and parietal layers, conveying some degree of mobility for the testes.

The testes have a tough fibrous outer surface called the tunica albuginea. On the internal, posterior aspect of the fibrous there is a ridge called the mediastinum of the testis. Fibrous septa extend from this ridge between lobules formed by seminiferous tubules. Spermatozoa are produced inside these tubes. Straight tubules join the seminiferous tubules to the rete testis, which are canals situated in the mediastinum of the testes.

These glands receive their blood supply from the testicular arteries, originating from the abdominal aorta. The venous drainage is via the pampiniform venous plexus, which surrounds the testicular artery. The plexi of each testis join to form the left and right testicular veins.  They drain into the left renal vein and inferior vena cava, respectively. Innervation of the testes is via the testicular plexus, which originates from the renal and aortic plexi.

Ovaries

The ovaries are almond-shaped glands in which oocytes develop and produce the female hormones. Each one is suspended by the mesovarium, a peritoneal fold subdivision of the broad ligament of the uterus. Before puberty, the surface of the ovary is covered by the ovarian mesothelium, also known as surface epithelium, giving it a shiny appearance. This structure consists of a single layer of cuboidal cells. After puberty, the surface of the ovary becomes scarred due to ovulation, which involves ruptures of ovarian follicles and oocyte discharge.

The ovaries lie suspended inside the pelvic cavity on each side of the uterus, close to the lateral wall of the pelvis. Specifically, they are located inside the ovarian fossa. Attached to the superolateral aspect of the ovary is the suspensory ligament of the ovary. This is a peritoneal fold enclosing the ovarian vessels, lymphatics, and nerves, which become continuous with the mesovarium. The ligament of the ovary passes through the mesovarium, keeping the ovary attached to the uterus. It is the remnant of the ovarian gubernaculum of the fetus.

Blood supply to the ovaries is via the ovarian arteries arising from the abdominal aorta. Venous drainage is via the pampiniform venous plexus inside the broad ligament. The veins from the plexus join to form the ovarian veins, which accompany the ovarian arteries. The right ovarian vein drains in the inferior vena cava, while the left one drains in the left renal vein. Innervation is from the ovarian plexus.

Functions  

Sex hormones are produced in these organs as a result of LH and FSH production by the pituitary gland. The hormones they produce are important in sexual development, reproduction, and regulation of the menstrual cycle.

The two key hormones produced by the ovaries are estrogen and progesterone. Their production is triggered by the release of hormones by the hypothalamus. There are three types of estrogen: estradiol, estrone, and estriol. These combine to ensure healthy sexual development and fertility. Estradiol is important in breast development, fat distribution, and development of the reproductive organs. Progesterone is most important during pregnancy and ovulation, where it ensures that the lining of the uterus is suitable for foetus growth.

In males, testosterone is produced by the testes. Testosterone enhances bone growth, hair growth, and the development of sexual organs during puberty. Testosterone is also important in increasing muscle strength.

Highlights

  • The endocrine system is a collection of glands that secrete a variety of hormones, which travel to specific target organs via the bloodstream. Endocrine glands tend to be vascular and do not have ducts. The hormones of endocrine glands are stored in vacuoles or granules, ready to be released.
  • The hypothalamus is the endocrine system’s control center. It can be divided into chiasmatic, tuberal and mammillary bodies regions. Its control over the endocrine system is via direct projections to the neurohypophysis and indirect ones to the adenohypophysis.
  • The pituitary gland is located within the pituitary fossa, partially covered by the diaphragma sellae. It is divided into an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis). The secretion of the hypophysis is controlled directly by the hypothalamus via tracts to the neurohypophysis and indirectly, via the hypophyseal portal system, to the adenohypophysis.
  • The pineal gland is located at the level of the superior colliculi. It consists of pinealocytes that produce melatonin, an important hormone in the sleep-wake cycle. 
  • The thyroid gland is the largest endocrine gland and it is located in the neck at the level of C5-T1 vertebrae. It consists of two lobes joined together by an isthmus. It produces the hormones thyroxine, triiodothyronine and calcitonin.
  • The parathyroid glands are located on the posterior surface of the thyroid gland. There are two superior and two inferior ones. These glands produce the parathyroid hormone.
  • The enteric endocrine system is located in the gastrointestinal tract. The pancreas comprises an important part of it, secreting the hormones insulin and glucagon. This gland has a head, a neck, a body and a tail. It releases its hormones within the main pancreatic duct, which opens in the duodenum. 
  • The adrenal glands are located on top of the kidneys, from which they are separated by a septum. The glands consist of an outer part (adrenal cortex) and inner part (adrenal medulla). The adrenal cortex produces glucocorticoids, while the adrenal medulla produces adrenaline and epinephrine.
  • The testes and ovaries are considered as the endocrine organs of the reproductive systems. The testes produce spermatozoa and mainly the hormone testosterone. They are suspended in the scrotum by the spermatic cord. The ovaries are the site for oocyte development and the production of estrogen and progesterone hormones. The ovaries are located in the ovarian fossa.

Organs of the endocrine system: want to learn more about it?

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Show references

References:


  • K. L. Moore, A. F. Dalley, A. M. R. Agur: Clinically Oriented Anatomy, 7th  edition, Lippincott Williams & Wilkins

  • Susan Standring: Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st edition, Elsevier

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Overview of the Endocrine System

Overview of the Endocrine System

The endocrine system is a system of ductless glands that secrete hormones—chemical messengers that are carried for long distances.

Learning Objectives

Produce a brief overview of the endocrine system

Key Takeaways

Key Points
  • The endocrine system is a system of ductless glands that secrete hormones directly into the circulatory system to be carried long distances to other target organs that regulate key body and organ functions.
  • The major endocrine glands include the pituitary, pineal, ovaries, testes, thyroid, hypothalamus, and adrenal glands.
Key Terms
  • hormone: A molecule released by a cell or a gland in one part of the body that sends out messages affecting cells in other parts of the organism.
  • endocrine system: The system of ductless glands that secretes hormones directly into the circulatory system.

The Endocrine System

The endocrine system is a system of ductless glands that secretes hormones directly into the circulatory system to be carried long distances to other target organs regulating key body and organ functions. For example, the pineal gland, located at the base of the brain, secretes the hormone melatonin, responsible for regulating sleep patterns.

Endocrine glands are typically well vascularized and the cells comprising the tissue are typically rich in intracellular vacuoles or granules that store hormones prior to release. Endocrine signaling is typically slow to initiate but is prolonged in response; this provides a counterpoint to the more rapid and short-lived nervous system signals.

The endocrine system is in contrast to the exocrine system, which features ducted glands that secrete substances onto an epithelial surface; for example, a sweat gland. Additionally the endocrine system is differentiated from shorter distance signaling such as autocrine (a cell affecting itself), juxtacrine (a cell affecting it’s direct neighbors), and paracrine (a cell affecting other nearby cells) signaling.

Key Endocrine Glands

The major endocrine glands include the pituitary, pineal, ovaries, testes, thyroid, hypothalamus and adrenal glands, additionally other tissues such as the kidney and liver also display secondary adrenal functions.

Endocrine glands of the head and neck: The endocrine systems found in the head and neck include the hypothalamus, pineal, pituitary and thyroid glands.

Comparing the Nervous and Endocrine Systems

The nervous system and endocrine system both use chemical messengers to signal cells, but each has a different transmission speed.

Learning Objectives

Distinguish between the nervous system and the endocrine system

Key Takeaways

Key Points
  • The nervous system can respond quickly to stimuli, through the use of action potentials and neurotransmitters.
  • Responses to nervous system stimulation are typically quick but short lived.
  • The endocrine system responds to stimulation by secreting hormones into the circulatory system that travel to the target tissue. 
  • Responses to endocrine system stimulation are typically slow but long lasting.
Key Terms
  • hormone: A molecule released by a cell or a gland in one part of the body that sends out messages affecting cells in other parts of the organism.
  • neurotransmitters: Endogenous chemicals that transmit signals from a neuron to a target cell across a synapse.

The body must maintain a constant internal environment, through a process termed homeostasis, while also being able to respond and adapt to external events. The nervous and endocrine systems both work to bring about this adaptation, but their response patterns are different. The nervous system and the endocrine system use chemical messengers to signal cells, but the speed at which these messages are transmitted and the length of their effects differs.

Nervous System

The nervous system responds rapidly to stimuli by sending electrical action potentials along neurons, which in turn transmit these action potentials to their target cells using neurotransmitters, the chemical messenger of the nervous system. The response to stimuli by the nervous system is near instantaneous, although the effects are often short lived. An example is the recoil mechanism of an arm when touching something hot.

Endocrine System

The endocrine system relies on hormones to elicit responses from target cells. These hormones are synthesized in specialized glands at a distance from their target, and travel through the bloodstream or inter-cellular fluid. Upon reaching their target, hormones can induce cellular responses at a protein or genetic level.

This process takes significantly longer than that of the nervous system, as endocrine hormones must first be synthesized, transported to their target cell, and enter or signal the cell. However, although hormones act more slowly than a nervous impulse, their effects are typically longer lasting. 

Additionally, the target cells can respond to minute quantities of hormones and are sensitive to subtle changes in hormone concentration. For example, the growth hormones secreted by the pituitary gland are responsible for sustained growth during childhood.

17.1 An Overview of the Endocrine System – Anatomy & Physiology

Learning Objectives

By the end of this section, you will be able to:

  • Distinguish similarities and differences between neural and hormonal communication
  • Identify the major organs of the endocrine system and their location in the body

Communication within the human body involves the transmission of signals to control and coordinate actions in an effort to maintain homeostasis.  There are two major organ systems responsible for providing these communication pathways: the nervous system and the endocrine system.

The nervous system is primarily responsible for rapid communication throughout the body.  As discussed in previous chapters, the nervous system utilizes two types of signals – electrical and chemical (Table 17.1).  Electrical signals are sent via the generation and propagation of action potentials which move along the membrane of a cell.  Once the action potential reaches the synaptic terminal, the electrical signal is converted to a chemical signal as neurotransmitters are released into the synaptic cleft.  When the neurotransmitters binds with receptors on the receiving (post-synaptic) cell, a new electrical signal is generated and quickly continues on to its destination.  In this way, neural communication enables body functions that involve quick, brief actions, such as movement, sensation, and cognition.

In contrast, the endocrine system relies on only a single method of communication: chemical signaling (Table 1).  Hormones are the chemicals released by endocrine cells that regulate other cells in the body.   Hormones are transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, triggering a response.  Because of this dependence on the cardiovascular system for transport, this type of communication is much slower than that observed for neural signaling.  As such, hormonal communication is usually associated with activities that go on for relatively long periods of time.

External Website

Visit this link to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. What is the secondary messenger made by adenylyl cyclase during the activation of liver cells by epinephrine?

In general, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting—taking care of the internal environment of the body, maintaining homeostasis, and controlling reproduction. This does not mean, however, that the two systems are completely independent of one another.  Take for example the release of adrenaline from the adrenal medulla as part of the ‘fight-or-flight’ response.  Although adrenaline uses blood for transportation throughout the body, the effects are evident within seconds after the event has occurred;  how does the response happen so quickly if hormones are usually slower acting?   It occurs so rapidly because the nervous and endocrine system are both involved in the process: it is the fast action of the nervous system responding to the danger in the environment that stimulates the adrenal glands to quickly secrete their hormones.  In such a situation, the nervous system causes a rapid endocrine response to deal with sudden changes in both the external and internal environments when necessary.

Endocrine and Nervous Systems (Table 17.1)
Endocrine system Nervous system
Signaling mechanism(s) Chemical Chemical/electrical
Primary chemical signal Hormones Neurotransmitters
Distance traveled Long or short Always short
Response time Fast or slow Always fast
Environment targeted Internal Internal and external

Hormones are released by secretory cells that are derived from epithelial tissue.  Often, these cells are clustered together, forming endocrine glands.  Unlike exocrine glands, which have a duct for conveying secretions to the outside of the body (e.g., sweat gland), endocrine glands secrete substances directly into the surrounding interstitial fluid.  From there, hormones then enter the bloodstream for distribution throughout the body.

The major endocrine glands found in the human body include the pituitary gland, thyroid gland, parathyroid glands, thymus gland, adrenal glands, pineal gland, testes, and ovaries (Figure 17. 1.1). While some of the glands are pure endocrine (e.g., thyroid gland), others serve both endocrine and exocrine function. For example, the pancreas contains cells that secrete digestive enzymes and juices into the small intestine (exocrine function) and cells that secrete the hormones insulin and glucagon, which regulate blood glucose levels.

In addition to the endocrine glands, major organs of the body show endocrine function including the hypothalamus, heart, kidneys, stomach, small intestine, and liver.  Moreover, adipose tissue has long been known to produce hormones, and recent research has revealed a role for bone tissue in hormone production and secretion.

Figure 17.1.1 – Endocrine System: Endocrine glands and cells are located throughout the body and play an important role in homeostasis.

In the classical definition of the endocrine system, hormones are secreted into the interstitial fluid and then diffuse into the blood or lymph for circulation throughout the body to reach target tissues.  However, in certain instances, target cells are local and do not require hormones to enter the blood.  If a chemical signal is released into the interstitial fluid and targets neighboring cells, then the activity is referred to as paracrine.  Neurotransmitter communication between a pre- and post-synaptic neuron is a good example of paracrine activity.  Alternatively, chemicals released by a cell elicit a response in the same cell that secreted it, demonstrating autocrine activity.  An example of this is type of activity is Interleukin-1, signaling molecule released in an inflammatory response that binds to receptors located on the surface of the cell releasing the molecule.

Career Connections – 

Endocrinologist

Endocrinology is a specialty in the field of medicine that focuses on the treatment of endocrine system disorders. Endocrinologists, the medical doctors who specialize in this field, are experts in treating diseases associated with hormonal systems, ranging from thyroid disease to diabetes mellitus.

Patients who are referred to endocrinologists may have signs and symptoms or blood test results that suggest excessive or impaired functioning of an endocrine gland or endocrine cells. The endocrinologist may order additional blood tests to determine whether the patient’s hormonal levels are abnormal, or they may stimulate or suppress the function of the suspect endocrine gland and then have blood taken for analysis. Treatment varies according to the diagnosis. Some endocrine disorders, such as type 2 diabetes, may respond to lifestyle changes such as modest weight loss, adoption of a healthy diet, and regular physical activity. Other disorders may require medication, such as hormone replacement, and routine monitoring by the endocrinologist. These include disorders of the pituitary gland that can affect growth and disorders of the thyroid gland that can result in a variety of metabolic problems.

Some patients experience health problems as a result of the normal decline in hormones that can accompany aging. These patients can consult with an endocrinologist to weigh the risks and benefits of hormone replacement therapy intended to boost their natural levels of reproductive hormones.

In addition to treating patients, endocrinologists may be involved in research to improve the understanding of endocrine system disorders and develop new treatments for these diseases.

Chapter Review

The body coordinates its functions through two major types of communication: neural and endocrine. Neural communication includes both electrical and chemical signaling between neurons and target cells. Endocrine communication involves chemical signaling via the release of hormones which travel through the bloodstream, where they elicit a response in target cells. Endocrine glands are ductless glands that secrete hormones. Many organs of the body with other primary functions—such as the heart, stomach, and kidneys—also have endocrine activity.

Interactive Link Questions

Visit this link to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. What is the secondary messenger made by adenylyl cyclase during the activation of liver cells by epinephrine?

Critical Thinking Questions

1. Describe several main differences in the communication methods used by the endocrine system and the nervous system.

2. Compare and contrast endocrine and exocrine glands.

3. True or false: Neurotransmitters are a special class of paracrines. Explain your answer.

Glossary

autocrine
chemical signal that elicits a response in the same cell that secreted it
endocrine gland
tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion
endocrine system
cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes
exocrine system
cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts
hormone
secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body
paracrine
chemical signal that elicits a response in neighboring cells; also called paracrine factor

Solutions

Answers for Critical Thinking Questions

  1. The endocrine system uses chemical signals called hormones to convey information from one part of the body to a distant part of the body. Hormones are released from the endocrine cell into the extracellular environment, but then travel in the bloodstream to target tissues. This communication and response can take seconds to days. In contrast, neurons transmit electrical signals along their axons. At the axon terminal, the electrical signal prompts the release of a chemical signal called a neurotransmitter that carries the message across the synaptic cleft to elicit a response in the neighboring cell. This method of communication is nearly instantaneous, of very brief duration, and is highly specific.
  2. Endocrine glands are ductless. They release their secretion into the surrounding fluid, from which it enters the bloodstream or lymph to travel to distant cells. Moreover, the secretions of endocrine glands are hormones. Exocrine glands release their secretions through a duct that delivers the secretion to the target location. Moreover, the secretions of exocrine glands are not hormones, but compounds that have an immediate physiologic function. For example, pancreatic juice contains enzymes that help digest food.
  3. True. Neurotransmitters can be classified as paracrines because, upon their release from a neuron’s axon terminals, they travel across a microscopically small cleft to exert their effect on a nearby neuron or muscle cell.

Endocrine System – Building a Medical Terminology Foundation

  • Identify the anatomy of the endocrine system
  • Describe the main functions of the endocrine system
  • Spell the medical terms of the endocrine system and use correct abbreviations
  • Identify the medical specialties associated with the endocrine system
  • Explore common diseases, disorders, and procedures related to the endocrine system

Endocrine System Word Parts

Click on prefixes, combining forms, and suffixes to reveal a list of word parts to memorize for the Endocrine System.

Introduction to Endocrine System

Figure 20.1 A Child Catches a Falling Leaf. Hormones of the endocrine system coordinate and control growth, metabolism, temperature regulation, the stress response, reproduction, and many other functions. (credit: “seenthroughmylense”/flickr.com). From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

You may never have thought of it this way, but when you send a text message to two friends to meet you at the dining hall at six, you’re sending digital signals that (you hope) will affect their behaviour—even though they are some distance away. Similarly, certain cells send chemical signals to other cells in the body that influence their behaviour. This long-distance intercellular communication, coordination, and control is critical to maintain equilibrium (homeostasis). This intercellular activity is the fundamental function of the endocrine system.

Watch this video:

Media 20.1 Endocrine System, Part 1 – Glands & Hormones: Crash Course A&P #23 [Online video]. Copyright 2015 by CrashCourse.

Endocrine System Medical Terms

Anatomy (Structures) of the Endocrine System

The endocrine system consists of cells, tissues, and organs that secrete hormones as a primary or secondary function. The endocrine gland is the major player in this system. The primary function of the endocrine gland is to secrete hormones directly into the surrounding fluid. The surrounding fluid (interstitial fluid) and the blood vessels then transport the hormones throughout the body. The endocrine system includes the pituitary, thyroid, parathyroid, adrenal, and pineal glands (see Figure 20.2). Some of these glands have both endocrine and non-endocrine functions. For example, the pancreas contains cells that function in digestion as well as cells that secrete the endocrine hormones like insulin and glucagon, which regulate blood glucose levels. The hypothalamus, thymus, heart, kidneys, stomach, small intestine, liver, skin, female ovaries, and male testes are other organs that contain cells with endocrine function. Moreover, fat (adipose) tissue has long been known to produce hormones, and recent research has revealed that even bone tissue has endocrine functions.

Figure 20.2 Endocrine System. Endocrine glands and cells are located throughout the body and play an important role in maintaining equilibrium (homeostasis). From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

The ductless endocrine glands are not to be confused with the body’s exocrine system, whose glands release their secretions through ducts. Examples of exocrine glands include the sebaceous and sweat glands of the skin. As just noted, the pancreas also has an exocrine function: most of its cells secrete pancreatic juice through the pancreatic and accessory ducts to the lumen of the small intestine.

Anatomy Labeling Activity

Physiology (Function) of the Endocrine System

Endocrine Signaling

The endocrine system uses one method of communication called chemical signaling. These chemical signals are sent by the endocrine organs. The endocrine organs secrete chemicals—called hormones—into the fluid outside of the tissue cells (extracellular fluid). Hormones are then transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, creating a particular response. For example, the hormones released when you are presented with a dangerous or a frightening situation, called the fight-or-flight response, occurs through the release of hormones from the adrenal gland—epinephrine and norepinephrine—within seconds. In contrast, it may take up to 48 hours for target cells to respond to certain reproductive hormones.

In addition, endocrine signaling is typically less specific than neural (nerve) signaling. The same hormone may also play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone oxytocin generates uterine contractions in women who are in labour. This hormone is also important in generating the milk release reflex during breastfeeding, and may be involved in the sexual response and in feelings of emotional attachment in both males and females.

Generally, the nervous system involves quick responses to rapid changes in the external environment, and the endocrine system is usually slower acting—taking care of the internal environment of the body, maintaining equilibrium (homeostasis), and in controlling reproduction (see Table 20.1). So how does the fight-or-flight response, that was mentioned earlier, happen so quickly if hormones are usually slower acting? It is because the two systems are connected. It is the fast action of the nervous system in response to the danger in the environment that stimulates the adrenal glands to secrete their hormones, epinephrine and norepinephrine. As a result, the nervous system can cause rapid endocrine responses to keep up with sudden changes in both the external and internal environments, when necessary.

Table 20.1: Endocrine and Nervous Systems. From Betts, et al., 2013. Licensed under CC BY 4.0.
Characteristic Endocrine System Nervous System
Signaling mechanism(s) Chemical Chemical/electrical
Primary chemical signal Hormones Neurotransmitters
Distance traveled Long or short Always short
Response time Fast or slow Always fast
Environment targeted Internal Internal and external

Other Types of Chemical Signaling

There are four different types of chemical signaling occurring in multicellular organisms: endocrine signaling, autocrine signaling, paracrine signaling, and direct signaling.

In endocrine signaling, hormones secreted into the extracellular fluid spreads into the blood or lymphatic system, and can, therefore, travel great distances throughout the body.

In contrast, autocrine signaling occurs within the same cell. An autocrine (auto- = “self”) is a chemical that triggers a response in the same cell that secreted the chemical. For example, Interleukin-1 (or IL-1), is a chemical signaling molecule that plays a role in inflammation. The cells that release IL-1 also have receptors on their surface that bind IL-1, resulting in autocrine signaling.

Paracrine signaling occurs amongst neighbouring cells. A paracrine (para- = “near”) is a chemical that triggers a response in neighbouring cells. Although paracrines may enter the bloodstream, their concentration is generally too low to elicit a response from distant tissues. A familiar example for those with asthma is histamine, a paracrine that is released by immune cells. Histamine causes the smooth muscle cells of the lungs to constrict, narrowing the airways.

Direct signaling occurs between neighbouring cells across gap junctions. Gap junctions are channels that connect neighbouring cells, that allow small molecules to move between the neighbouring cells.

  • Describe the communication methods used by the endocrine system.
  • Compare and contrast endocrine and exocrine glands.
  • True or false: Neurotransmitters are a special class of paracrines? Explain your answer.

Hormones

Although a given hormone may travel throughout the body in the bloodstream, it will affect the activity only of its target cells; that is, cells with receptors for that particular hormone. Once the hormone binds to the receptor, a chain of events is initiated that leads to the target cell’s response. Hormones play a critical role in the regulation of physiological processes because of the target cell responses they regulate. These responses contribute to human reproduction, growth and development of body tissues, metabolism, fluid, and electrolyte balance, sleep, and many other body functions. The major hormones of the human body and their effects are identified in Table 20.2.

Table 20.2: Endocrine Glands and Their Major Hormones. From Betts, et al., 2013. Licensed under CC BY 4.0.
Endocrine Gland Associated Hormones Chemical Class Effect
Pituitary (anterior) Growth hormone (GH) Protein Promotes growth of body tissues
Pituitary (anterior) Prolactin (PRL) Peptide Promotes milk production
Pituitary (anterior) Thyroid-stimulating hormone (TSH) Glycoprotein Stimulates thyroid hormone release
Pituitary (anterior) Adrenocorticotropic hormone (ACTH) Peptide Stimulates hormone release by adrenal cortex
Pituitary (anterior) Follicle-stimulating hormone (FSH) Glycoprotein Stimulates gamete production
Pituitary (anterior) Luteinizing hormone (LH) Glycoprotein Stimulates androgen production by gonads
Pituitary (posterior) Antidiuretic hormone (ADH) Peptide Stimulates water reabsorption by kidneys
Pituitary (posterior) Oxytocin Peptide Stimulates uterine contractions during childbirth
Thyroid Thyroxine (T4), triiodothyronine (T3) Amine Stimulate basal metabolic rate
Thyroid Calcitonin Peptide Reduces blood Ca2+ levels
Parathyroid Parathyroid hormone (PTH) Peptide Increases blood Ca2+ levels
Adrenal (cortex) Aldosterone Steroid Increases blood Na+ levels
Adrenal (cortex) Cortisol, corticosterone, cortisone Steroid Increase blood glucose levels
Adrenal (medulla) Epinephrine, norepinephrine Amine Stimulate fight-or-flight response
Pineal Melatonin Amine Regulates sleep cycles
Pancreas Insulin Protein Reduces blood glucose levels
Pancreas Glucagon Protein Increases blood glucose levels
Testes Testosterone Steroid Stimulates development of male secondary sex characteristics and sperm production
Ovaries Estrogens and progesterone Steroid Stimulate development of female secondary sex characteristics and prepare the body for childbirth
Types of Hormones

The hormones of the human body can be divided into two major groups on the basis of their chemical structure. Hormones derived from amino acids include amines, peptides, and proteins. Those derived from lipids include steroids (see Table 20.3). These chemical groups affect a hormone’s distribution, the type of receptors it binds to, and other aspects of its function.

Table 20.3 Amine, Peptide, Protein, and Steroid Hormone Structure. Adapted from Betts, et al., 2013. Licensed under CC BY 4.0.
HORMONE CLASS COMPONENTS EXAMPLES
Amine Hormone Amino acids with modified groups (e.g. norepinephrine’s carboxyl group is replaced with a benezene ring) Norepinephrine cellular structure.
Peptide Hormone Short chains of linked amino acids Oxytocin cellular structure.
Protein Hormone Long chains of linked amino acides Human growth hormone illustration.
Steroid Hormones Derived from 4ipid cholesterol Testosterone and progesterone cellular structure.
Amine Hormones

Hormones derived from the modification of amino acids are referred to as amine hormones. Amine hormones are synthesized from the amino acids tryptophan or tyrosine. An example of a hormone derived from tryptophan is melatonin, which is secreted by the pineal gland and helps regulate circadian rhythm.

Peptide and Protein Hormones

Whereas the amine hormones are derived from a single amino acid, peptide and protein hormones consist of multiple amino acids that link to form an amino acid chain. Examples of peptide hormones include antidiuretic hormone (ADH), a pituitary hormone important in fluid balance. Some examples of protein hormones include growth hormone, which is produced by the pituitary gland, and follicle-stimulating hormone (FSH). FSH helps stimulate the maturation of eggs in the ovaries and sperm in the testes.

Steroid Hormones

The primary hormones derived from lipids are steroids. Steroid hormones are derived from the lipid cholesterol. For example, the reproductive hormones testosterone and the estrogens—which are produced by the gonads (testes and ovaries)—are steroid hormones. The adrenal glands produce the steroid hormone aldosterone, which is involved in osmoregulation, and cortisol, which plays a role in metabolism.

Like cholesterol, steroid hormones are not soluble in water (they are hydrophobic). Because blood is water-based, lipid-derived hormones must travel to their target cell bound to a transport protein.

Pathways of Hormone Action

The message a hormone sends is received by a hormone receptor, a protein located either inside the cell or within the cell membrane. The receptor will process the message by initiating other signaling events or cellular mechanisms that result in the target cell’s response. Hormone receptors recognize molecules with specific shapes and side groups, and respond only to those hormones that are recognized. The same type of receptor may be located on cells in different body tissues, and trigger somewhat different responses. Thus, the response triggered by a hormone depends not only on the hormone, but also on the target cell.

Once the target cell receives the hormone signal, it can respond in a variety of ways. The response may include the stimulation of protein synthesis, activation or deactivation of enzymes, alteration in the permeability of the cell membrane, altered rates of mitosis and cell growth, and stimulation of the secretion of products. Moreover, a single hormone may be capable of inducing different responses in a given cell.

Factors Affecting Target Cell Response

You will recall that target cells must have receptors specific to a given hormone if that hormone is to trigger a response. But several other factors influence the target cell response. For example, the presence of a significant level of a hormone circulating in the bloodstream can cause its target cells to decrease their number of receptors for that hormone. This process is called downregulation, and it allows cells to become less reactive to the excessive hormone levels. When the level of a hormone is chronically reduced, target cells engage in upregulation to increase their number of receptors. This process allows cells to be more sensitive to the hormone that is present. Cells can also alter the sensitivity of the receptors themselves to various hormones.

Two or more hormones can interact to affect the response of cells in a variety of ways. The three most common types of interaction are as follows:

  • The permissive effect, in which the presence of one hormone enables another hormone to act. For example, thyroid hormones have complex permissive relationships with certain reproductive hormones. A dietary deficiency of iodine, a component of thyroid hormones, can therefore affect reproductive system development and functioning.
  • The synergistic effect, in which two hormones with similar effects produce an amplified response. In some cases, two hormones are required for an adequate response. For example, two different reproductive hormones—FSH from the pituitary gland and estrogens from the ovaries—are required for the maturation of female ova (egg cells).
  • The antagonistic effect, in which two hormones have opposing effects. A familiar example is the effect of two pancreatic hormones, insulin and glucagon. Insulin increases the liver’s storage of glucose as glycogen, decreasing blood glucose, whereas glucagon stimulates the breakdown of glycogen stores, increasing blood glucose.
  • Describe how a hormone receptor functions and reacts to messages received.
  • Contrast upregulation and downregulation. Are both of these processes necessary?  Why or why not?
Regulation of Hormone Secretion

To prevent abnormal hormone levels and a potential disease state, hormone levels must be tightly controlled. The body maintains this control by balancing hormone production and degradation. Feedback loops govern the initiation and maintenance of most hormone secretion in response to various stimuli.

Role of Feedback Loops

The contribution of feedback loops to homeostasis will only be briefly reviewed here. Positive feedback loops are characterized by the release of additional hormone in response to an original hormone release. The release of oxytocin during childbirth is a positive feedback loop. The initial release of oxytocin begins to signal the uterine muscles to contract, which pushes the fetus toward the cervix, causing it to stretch. This, in turn, signals the pituitary gland to release more oxytocin, causing labor contractions to intensify. The release of oxytocin decreases after the birth of the child.

The more common method of hormone regulation is the negative feedback loop. Negative feedback is characterized by the inhibition of further secretion of a hormone in response to adequate levels of that hormone. This allows blood levels of the hormone to be regulated within a narrow range. An example of a negative feedback loop is the release of glucocorticoid hormones from the adrenal glands, as directed by the hypothalamus and pituitary gland. As glucocorticoid concentrations in the blood rise, the hypothalamus and pituitary gland reduce their signaling to the adrenal glands to prevent additional glucocorticoid secretion (see Figure 20.3).

Figure 20.3 Negative Feedback Loop. The release of adrenal glucocorticoids is stimulated by the release of hormones from the hypothalamus and pituitary gland. This signaling is inhibited when glucocorticoid levels become elevated by causing negative signals to the pituitary gland and hypothalamus. From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

Anterior Pituitary Gland

The anterior pituitary originates from the digestive tract in the embryo and migrates toward the brain during fetal development. There are three regions: the pars distalis is the most anterior, the pars intermedia is adjacent to the posterior pituitary, and the pars tuberalis is a slender “tube” that wraps the infundibulum.

Recall that the posterior pituitary does not synthesize hormones, but merely stores them. In contrast, the anterior pituitary does manufacture hormones. However, the secretion of hormones from the anterior pituitary is regulated by two classes of hormones. These hormones—secreted by the hypothalamus—are the releasing hormones that stimulate the secretion of hormones from the anterior pituitary and the inhibiting hormones that inhibit secretion.

Hypothalamic hormones are secreted by neurons, but enter the anterior pituitary through blood vessels. Within the infundibulum is a bridge of capillaries that connects the hypothalamus to the anterior pituitary. This network, called the hypophyseal portal system, allows hypothalamic hormones to be transported to the anterior pituitary without first entering the systemic circulation. The system originates from the superior hypophyseal artery, which branches off the carotid arteries and transports blood to the hypothalamus. The branches of the superior hypophyseal artery form the hypophyseal portal system (see Figure 20.4). Hypothalamic releasing and inhibiting hormones travel through a primary capillary plexus to the portal veins, which carry them into the anterior pituitary. Hormones produced by the anterior pituitary (in response to releasing hormones) enter a secondary capillary plexus, and from there drain into the circulation.

Figure 20.4 Anterior Pituitary. The anterior pituitary manufactures seven hormones. The hypothalamus produces separate hormones that stimulate or inhibit hormone production in the anterior pituitary. Hormones from the hypothalamus reach the anterior pituitary via the hypophyseal portal system. From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

The anterior pituitary produces seven hormones. These are the growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), beta endorphin, and prolactin. Of the hormones of the anterior pituitary, TSH, ACTH, FSH, and LH are collectively referred to as tropic hormones (trope- = “turning”) because they turn on or off the function of other endocrine glands.

Growth Hormone

The endocrine system regulates the growth of the human body, protein synthesis, and cellular replication. A major hormone involved in this process is growth hormone (GH), also called somatotropin—a protein hormone produced and secreted by the anterior pituitary gland. Its primary function is anabolic; it promotes protein synthesis and tissue building through direct and indirect mechanisms (see Figure 20.5). GH levels are controlled by the release of GHRH and GHIH (also known as somatostatin) from the hypothalamus.

Figure 20.5 Hormonal Regulation of Growth. Growth hormone (GH) directly accelerates the rate of protein synthesis in skeletal muscle and bones. Insulin-like growth factor 1 (IGF-1) is activated by growth hormone and indirectly supports the formation of new proteins in muscle cells and bone. From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

A glucose-sparing effect occurs when GH stimulates lipolysis, or the breakdown of adipose tissue, releasing fatty acids into the blood. As a result, many tissues switch from glucose to fatty acids as their main energy source, which means that less glucose is taken up from the bloodstream.

GH also initiates the diabetogenic effect in which GH stimulates the liver to break down glycogen to glucose, which is then deposited into the blood. The name “diabetogenic” is derived from the similarity in elevated blood glucose levels observed between individuals with untreated diabetes mellitus and individuals experiencing GH excess. Blood glucose levels rise as the result of a combination of glucose-sparing and diabetogenic effects.

GH indirectly mediates growth and protein synthesis by triggering the liver and other tissues to produce a group of proteins called insulin-like growth factors (IGFs). These proteins enhance cellular proliferation and inhibit apoptosis, or programmed cell death. IGFs stimulate cells to increase their uptake of amino acids from the blood for protein synthesis. Skeletal muscle and cartilage cells are particularly sensitive to stimulation from IGFs.

Dysfunction of the endocrine system’s control of growth can result in several disorders. For example, gigantism is a disorder in children that is caused by the secretion of abnormally large amounts of GH, resulting in excessive growth. A similar condition in adults is acromegaly, a disorder that results in the growth of bones in the face, hands, and feet in response to excessive levels of GH in individuals who have stopped growing. Abnormally low levels of GH in children can cause growth impairment—a disorder called pituitary dwarfism (also known as growth hormone deficiency).

Posterior Pituitary Gland

The posterior pituitary is actually an extension of the neurons of the nuclei of the hypothalamus. The cell bodies of these regions rest in the hypothalamus, but their axons descend as the hypothalamic–hypophyseal tract within the infundibulum, and end in axon terminals that comprise the posterior pituitary (see Figure 20.6).

Figure 20.6 Posterior Pituitary. Neurosecretory cells in the hypothalamus release oxytocin (OT) or ADH into the posterior lobe of the pituitary gland. These hormones are stored or released into the blood via the capillary plexus. From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

The posterior pituitary gland does not produce hormones, but rather stores and secretes hormones produced by the hypothalamus. The paraventricular nuclei produce the hormone oxytocin, whereas the supraoptic nuclei produce ADH. These hormones travel along the axons into storage sites in the axon terminals of the posterior pituitary. In response to signals from the same hypothalamic neurons, the hormones are released from the axon terminals into the bloodstream.

Oxytocin

When fetal development is complete, the peptide-derived hormone oxytocin (tocia- = “childbirth”) stimulates uterine contractions and dilation of the cervix. Throughout most of pregnancy, oxytocin hormone receptors are not expressed at high levels in the uterus. Toward the end of pregnancy, the synthesis of oxytocin receptors in the uterus increases, and the smooth muscle cells of the uterus become more sensitive to its effects. Oxytocin is continually released throughout childbirth through a positive feedback mechanism. As noted earlier, oxytocin prompts uterine contractions that push the fetal head toward the cervix. In response, cervical stretching stimulates additional oxytocin to be synthesized by the hypothalamus and released from the pituitary. This increases the intensity and effectiveness of uterine contractions and prompts additional dilation of the cervix. The feedback loop continues until birth.

Although the mother’s high blood levels of oxytocin begin to decrease immediately following birth, oxytocin continues to play a role in maternal and newborn health. First, oxytocin is necessary for the milk ejection reflex (commonly referred to as “let-down”) in breastfeeding women. As the newborn begins suckling, sensory receptors in the nipples transmit signals to the hypothalamus. In response, oxytocin is secreted and released into the bloodstream. Within seconds, cells in the mother’s milk ducts contract, ejecting milk into the infant’s mouth. Secondly, in both males and females, oxytocin is thought to contribute to parent–newborn bonding, known as attachment. Oxytocin is also thought to be involved in feelings of love and closeness, as well as in the sexual response.

Antidiuretic Hormone (ADH)

The solute concentration of the blood, or blood osmolarity, may change in response to the consumption of certain foods and fluids, as well as in response to disease, injury, medications, or other factors. Blood osmolarity is constantly monitored by osmoreceptors—specialized cells within the hypothalamus that are particularly sensitive to the concentration of sodium ions and other solutes.

In response to high blood osmolarity, which can occur during dehydration or following a very salty meal, the osmoreceptors signal the posterior pituitary to release antidiuretic hormone (ADH). The target cells of ADH are located in the tubular cells of the kidneys. Its effect is to increase epithelial permeability to water, allowing increased water reabsorption. The more water reabsorbed from the filtrate, the greater the amount of water that is returned to the blood and the less that is excreted in the urine. A greater concentration of water results in a reduced concentration of solutes. ADH is also known as vasopressin because, in very high concentrations, it causes constriction of blood vessels, which increases blood pressure by increasing peripheral resistance. The release of ADH is controlled by a negative feedback loop. As blood osmolarity decreases, the hypothalamic osmoreceptors sense the change and prompt a corresponding decrease in the secretion of ADH. As a result, less water is reabsorbed from the urine filtrate.

Interestingly, drugs can affect the secretion of ADH. For example, alcohol consumption inhibits the release of ADH, resulting in increased urine production that can eventually lead to dehydration and a hangover. A disease called diabetes insipidus is characterized by chronic underproduction of ADH that causes chronic dehydration. Because little ADH is produced and secreted, not enough water is reabsorbed by the kidneys. Although patients feel thirsty, and increase their fluid consumption, this doesn’t effectively decrease the solute concentration in their blood because ADH levels are not high enough to trigger water reabsorption in the kidneys. Electrolyte imbalances can occur in severe cases of diabetes insipidus.

Thyroid-Stimulating Hormone

The activity of the thyroid gland is regulated by thyroid-stimulating hormone (TSH), also called thyrotropin. TSH is released from the anterior pituitary in response to thyrotropin-releasing hormone (TRH) from the hypothalamus. As discussed shortly, it triggers the secretion of thyroid hormones by the thyroid gland. In a classic negative feedback loop, elevated levels of thyroid hormones in the bloodstream then trigger a drop in production of TRH and subsequently TSH.

Adrenocorticotropic Hormone

The adrenocorticotropic hormone (ACTH), also called corticotropin, stimulates the adrenal cortex (the more superficial “bark” of the adrenal glands) to secrete corticosteroid hormones such as cortisol. ACTH come from a precursor molecule known as pro-opiomelanotropin (POMC) which produces several biologically active molecules when cleaved, including ACTH, melanocyte-stimulating hormone, and the brain opioid peptides known as endorphins. The release of ACTH is regulated by the corticotropin-releasing hormone (CRH) from the hypothalamus in response to normal physiologic rhythms. A variety of stressors can also influence its release, and the role of ACTH in the stress response is discussed later in this chapter.

Follicle-Stimulating Hormone and Luteinizing Hormone

The endocrine glands secrete a variety of hormones that control the development and regulation of the reproductive system (these glands include the anterior pituitary, the adrenal cortex, and the gonads—the testes in males and the ovaries in females). Much of the development of the reproductive system occurs during puberty and is marked by the development of sex-specific characteristics in both male and female adolescents. Puberty is initiated by gonadotropin-releasing hormone (GnRH), a hormone produced and secreted by the hypothalamus. GnRH stimulates the anterior pituitary to secrete gonadotropins—hormones that regulate the function of the gonads. The levels of GnRH are regulated through a negative feedback loop; high levels of reproductive hormones inhibit the release of GnRH. Throughout life, gonadotropins regulate reproductive function and, in the case of women, the onset and cessation of reproductive capacity.

The gonadotropins include two glycoprotein hormones: follicle-stimulating hormone (FSH) stimulates the production and maturation of sex cells, or gametes, including ova in women and sperm in men. FSH also promotes follicular growth; these follicles then release estrogens in the female ovaries. Luteinizing hormone (LH) triggers ovulation in women, as well as the production of estrogens and progesterone by the ovaries. LH stimulates production of testosterone by the male testes.

Prolactin

As its name implies, prolactin (PRL) promotes lactation (milk production) in women. During pregnancy, it contributes to development of the mammary glands, and after birth, it stimulates the mammary glands to produce breast milk. However, the effects of prolactin depend heavily upon the permissive effects of estrogens, progesterone, and other hormones. And as noted earlier, the let-down of milk occurs in response to stimulation from oxytocin.

In a non-pregnant woman, prolactin secretion is inhibited by prolactin-inhibiting hormone (PIH), which is actually the neurotransmitter dopamine, and is released from neurons in the hypothalamus. Only during pregnancy do prolactin levels rise in response to prolactin-releasing hormone (PRH) from the hypothalamus.

Intermediate Pituitary: Melanocyte-Stimulating Hormone

The cells in the zone between the pituitary lobes secrete a hormone known as melanocyte-stimulating hormone (MSH) that is formed by cleavage of the pro-opiomelanocortin (POMC) precursor protein. Local production of MSH in the skin is responsible for melanin production in response to UV light exposure. The role of MSH made by the pituitary is more complicated. For instance, people with lighter skin generally have the same amount of MSH as people with darker skin. Nevertheless, this hormone is capable of darkening of the skin by inducing melanin production in the skin’s melanocytes. Women also show increased MSH production during pregnancy; in combination with estrogens, it can lead to darker skin pigmentation, especially the skin of the areolas and labia minora. Table 20.4 is a summary of the pituitary hormones and their principal effects.

Table 20.4 Major Pituitary Hormones. Major pituitary hormones and their target organs. Adapted from Betts, et al., 2013. Licensed under CC BY 4.0.
IMAGE OF GLANDS HORMONES
An image displaying the posterior pituitary gland Posterior Pituitary Hormones
Releasing hormone (hypothalamus) Pituitary Hormone Target Effects
ADH Stores ADH Kidneys, sweat glands, circulatory system Water balance
OT Female reproductive system Triggers uterine contractions during childbirth
An image displaying the Anterior Pituitary Gland Anterior Pituitary Hormones
Releasing hormone (hypothalamus) Pituitary Hormone Target Effects
GnRH LH Reproductive system Stimulates production of sex hormones by gonads
GnRH FSH Reproductive system stimulates production of sperm and eggs
TRH TSH Thyroid gland STimulates the release of thyroid hormone (TH), TH regulates metabolism
PRH (inhibited by PIH) PRL Mammary glands Promotes milk production
GHRH (inhibited by GHIH) GH Liver, bone, muscles Induces targets to produce insulin-like growth factors (IGF). IGFs stimulate body growth and higher metabolic rate.
CRH ACTH Adrenal glands Induces targets to produce glucocorticoids, which regulate metabolism and stress response

Pineal Gland

A tiny endocrine gland whose functions are not entirely clear. The pinealocyte cells that make up the pineal gland are known to produce and secrete the amine hormone melatonin, which is derived from serotonin.

The secretion of melatonin varies according to the level of light received from the environment. When photons of light stimulate the retinas of the eyes, a nerve impulse is sent to a region of the hypothalamus which is important in regulating biological rhythms. When blood levels of melatonin fall they promote wakefulness. In contrast, as light levels decline—such as during the evening—melatonin production increases, boosting blood levels and causing drowsiness.

Watch this video:

Media 20.2 What Does Melatonin Do? Melatonin Use Info [Online video]. Copyright 2015 by Travelers Defense.

What should you avoid doing in the middle of your sleep cycle that would lower melatonin?

The secretion of melatonin may influence the body’s circadian rhythms, the dark-light fluctuations that affect not only sleepiness and wakefulness, but also appetite and body temperature. Interestingly, children have higher melatonin levels than adults, which may prevent the release of gonadotropins from the anterior pituitary, thereby inhibiting the onset of puberty. Finally, an antioxidant role of melatonin is the subject of current research.

Jet lag occurs when a person travels across several time zones and feels sleepy during the day or wakeful at night. Traveling across multiple time zones significantly disturbs the light-dark cycle regulated by melatonin. It can take up to several days for melatonin synthesis to adjust to the light-dark patterns in the new environment, resulting in jet lag. Some air travelers take melatonin supplements to induce sleep.

Thyroid Gland

A butterfly-shaped organ, the thyroid gland is located anterior to the trachea, just inferior to the larynx (see Figure 20.7). The medial region, called the isthmus, is flanked by wing-shaped left and right lobes. Each of the thyroid lobes are embedded with parathyroid glands, primarily on their posterior surfaces. The tissue of the thyroid gland is composed mostly of thyroid follicles. The follicles are made up of a central cavity filled with a sticky fluid called colloid. Surrounded by a wall of epithelial follicle cells, the colloid is the center of thyroid hormone production, and that production is dependent on the hormones’ essential and unique component: iodine.

Figure 20.7 Thyroid Gland. The thyroid gland is located in the neck where it wraps around the trachea. (a) Anterior view of the thyroid gland. (b) Posterior view of the thyroid gland. (c) The glandular tissue is composed primarily of thyroid follicles. The larger parafollicular cells often appear within the matrix of follicle cells. LM × 1332. (Micrograph provided by the Regents of University of Michigan Medical School © 2012). From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

    Regulation of TH Synthesis

    The release of T3 and T4 from the thyroid gland is regulated by thyroid-stimulating hormone (TSH).  Low blood levels of T3 and T4 stimulate the release of thyrotropin-releasing hormone (TRH) from the hypothalamus, which triggers secretion of TSH from the anterior pituitary. In turn, TSH stimulates the thyroid gland to secrete T3 and T4. The levels of TRH, TSH, T3, and T4 are regulated by a negative feedback system in which increasing levels of T3 and T4 decrease the production and secretion of TSH. The thyroid hormones, T3 and T4, are often referred to as metabolic hormones because their levels influence the body’s basal metabolic rate, the amount of energy used by the body at rest.

    The thyroid gland also secretes a hormone called calcitonin that is produced by the parafollicular cells (also called C cells) that stud the tissue between distinct follicles. Calcitonin is released in response to a rise in blood calcium levels.

    Parathyroid Gland

    The parathyroid glands are tiny, round structures usually found embedded in the posterior surface of the thyroid gland. A thick connective tissue capsule separates the glands from the thyroid tissue. Most people have four parathyroid glands, but occasionally there are more in tissues of the neck or chest. The function of one type of parathyroid cells, the oxyphil cells, is not clear. The primary functional cells of the parathyroid glands are the chief cells. These epithelial cells produce and secrete the parathyroid hormone (PTH), the major hormone involved in the regulation of blood calcium levels.

    Adrenal Gland

    The adrenal glands are wedges of glandular and neuroendocrine tissue adhering to the top of the kidneys by a fibrous capsule (see Figure 20.8). The adrenal glands have a rich blood supply and experience one of the highest rates of blood flow in the body. They are served by several arteries branching off the aorta, including the suprarenal and renal arteries. Blood flows to each adrenal gland at the adrenal cortex and then drains into the adrenal medulla. Adrenal hormones are released into the circulation via the left and right suprarenal veins.

    Figure 20.8 Adrenal Glands. Both adrenal glands sit atop the kidneys and are composed of an outer cortex and an inner medulla, all surrounded by a connective tissue capsule. The cortex can be subdivided into additional zones, all of which produce different types of hormones. LM × 204. (Micrograph provided by the Regents of University of Michigan Medical School © 2012). From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.] 

    The adrenal cortex, as a component of the hypothalamic-pituitary-adrenal (HPA) axis, secretes steroid hormones important for the regulation of the long-term stress response, blood pressure and blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation. The HPA axis involves the stimulation of hormone release of adrenocorticotropic hormone (ACTH) from the pituitary by the hypothalamus. ACTH then stimulates the adrenal cortex to produce the hormone cortisol. This pathway will be discussed in more detail below.

    The adrenal medulla is neuroendocrine tissue composed of postganglionic sympathetic nervous system (SNS) neurons. It is really an extension of the autonomic nervous system, which regulates homeostasis in the body. The sympathomedullary (SAM) pathway involves the stimulation of the medulla by impulses from the hypothalamus via neurons from the thoracic spinal cord. The medulla is stimulated to secrete the amine hormones epinephrine and norepinephrine.

    One of the major functions of the adrenal gland is to respond to stress. Stress can be either physical or psychological or both. Physical stresses include exposing the body to injury, walking outside in cold and wet conditions without a coat on, or malnutrition. Psychological stresses include the perception of a physical threat, a fight with a loved one, or just a bad day at school.

    The body responds in different ways to short-term stress and long-term stress following a pattern known as the general adaptation syndrome (GAS). Stage one of GAS is called the alarm reaction. This is short-term stress, the fight-or-flight response, mediated by the hormones epinephrine and norepinephrine from the adrenal medulla via the SAM pathway. Their function is to prepare the body for extreme physical exertion. Once this stress is relieved, the body quickly returns to normal. The section on the adrenal medulla covers this response in more detail.

    If the stress is not soon relieved, the body adapts to the stress in the second stage called the stage of resistance. If a person is starving for example, the body may send signals to the gastrointestinal tract to maximize the absorption of nutrients from food.

    If the stress continues for a longer term however, the body responds with symptoms quite different than the fight-or-flight response. During the stage of exhaustion, individuals may begin to suffer depression, the suppression of their immune response, severe fatigue, or even a fatal heart attack. These symptoms are mediated by the hormones of the adrenal cortex, especially cortisol, released as a result of signals from the HPA axis.

    Adrenal hormones also have several non–stress-related functions, including the increase of blood sodium and glucose levels, which will be described in detail below.

    Adrenal Cortex

    The adrenal cortex consists of multiple layers of lipid-storing cells that occur in three structurally distinct regions. Each of these regions produces different hormones.

    Watch this video:

    Media 20.3 Endocrine System, Part 2 – Hormone Cascades: Crash Course A&P #24 [Online video]. Copyright 2015 by CrashCourse. 

     

    • Which hormone produced by the adrenal glands is responsible for the mobilization of energy stores?
    Hormones of the Zona Glomerulosa

    The most superficial region of the adrenal cortex is the zona glomerulosa, which produces a group of hormones collectively referred to as mineralocorticoids because of their effect on body minerals, especially sodium and potassium. These hormones are essential for fluid and electrolyte balance.

    Aldosterone is the major mineralocorticoid. It is important in the regulation of the concentration of sodium and potassium ions in urine, sweat, and saliva. For example, it is released in response to elevated blood K+, low blood Na+, low blood pressure, or low blood volume. In response, aldosterone increases the excretion of K+ and the retention of Na+, which in turn increases blood volume and blood pressure. Its secretion is prompted when CRH from the hypothalamus triggers ACTH release from the anterior pituitary.

    Aldosterone is also a key component of the renin-angiotensin-aldosterone system (RAAS) in which specialized cells of the kidneys secrete the enzyme renin in response to low blood volume or low blood pressure. Renin then catalyzes the conversion of the blood protein angiotensinogen, produced by the liver, to the hormone angiotensin I. Angiotensin I is converted in the lungs to angiotensin II by angiotensin-converting enzyme (ACE). Angiotensin II has three major functions:

    1. Initiating vasoconstriction of the arterioles, decreasing blood flow
    2. Stimulating kidney tubules to reabsorb NaCl and water, increasing blood volume
    3. Signaling the adrenal cortex to secrete aldosterone, the effects of which further contribute to fluid retention, restoring blood pressure and blood volume

    For individuals with hypertension, or high blood pressure, drugs are available that block the production of angiotensin II. These drugs, known as ACE inhibitors, block the ACE enzyme from converting angiotensin I to angiotensin II, thus mitigating the latter’s ability to increase blood pressure.

    Hormones of the Zona Fasciculata

    The intermediate region of the adrenal cortex is the zona fasciculata, named as such because the cells form small fascicles (bundles) separated by tiny blood vessels. The cells of the zona fasciculata produce hormones called glucocorticoids because of their role in glucose metabolism. The most important of these is cortisol, some of which the liver converts to cortisone. A glucocorticoid produced in much smaller amounts is corticosterone. In response to long-term stressors, the hypothalamus secretes CRH, which in turn triggers the release of ACTH by the anterior pituitary. ACTH triggers the release of the glucocorticoids. Their overall effect is to inhibit tissue building while stimulating the breakdown of stored nutrients to maintain adequate fuel supplies. In conditions of long-term stress, for example, cortisol promotes the catabolism of glycogen to glucose, the catabolism of stored triglycerides into fatty acids and glycerol, and the catabolism of muscle proteins into amino acids. These raw materials can then be used to synthesize additional glucose and ketones for use as body fuels. The hippocampus, which is part of the temporal lobe of the cerebral cortices and important in memory formation, is highly sensitive to stress levels because of its many glucocorticoid receptors.

    You are probably familiar with prescription and over-the-counter medications containing glucocorticoids, such as cortisone injections into inflamed joints, prednisone tablets and steroid-based inhalers used to manage severe asthma, and hydrocortisone creams applied to relieve itchy skin rashes. These drugs reflect another role of cortisol—the downregulation of the immune system, which inhibits the inflammatory response.

    Hormones of the Zona Reticularis

    The deepest region of the adrenal cortex is the zona reticularis, which produces small amounts of a class of steroid sex hormones called androgens. During puberty and most of adulthood, androgens are produced in the gonads. The androgens produced in the zona reticularis supplement the gonadal androgens. They are produced in response to ACTH from the anterior pituitary and are converted in the tissues to testosterone or estrogens. In adult women, they may contribute to the sex drive, but their function in adult men is not well understood. In post-menopausal women, as the functions of the ovaries decline, the main source of estrogens becomes the androgens produced by the zona reticularis.

    Adrenal Medulla

    As noted earlier, the adrenal cortex releases glucocorticoids in response to long-term stress such as severe illness. In contrast, the adrenal medulla releases its hormones in response to acute, short-term stress mediated by the sympathetic nervous system (SNS).

    The medullary tissue is composed of unique postganglionic SNS neurons called chromaffin cells, which are large and irregularly shaped, and produce the neurotransmitters epinephrine (also called adrenaline) and norepinephrine (or noradrenaline). Epinephrine is produced in greater quantities—approximately a 4 to 1 ratio with norepinephrine—and is the more powerful hormone. Because the chromaffin cells release epinephrine and norepinephrine into the systemic circulation, where they travel widely and exert effects on distant cells, they are considered hormones. Derived from the amino acid tyrosine, they are chemically classified as catecholamines.

    The secretion of medullary epinephrine and norepinephrine is controlled by a neural pathway that originates from the hypothalamus in response to danger or stress (the SAM pathway). Both epinephrine and norepinephrine signal the liver and skeletal muscle cells to convert glycogen into glucose, resulting in increased blood glucose levels. These hormones increase the heart rate, pulse, and blood pressure to prepare the body to fight the perceived threat or flee from it. In addition, the pathway dilates the airways, raising blood oxygen levels. It also prompts vasodilation, further increasing the oxygenation of important organs such as the lungs, brain, heart, and skeletal muscle. At the same time, it triggers vasoconstriction to blood vessels serving less essential organs such as the gastrointestinal tract, kidneys, and skin, and downregulates some components of the immune system. Other effects include a dry mouth, loss of appetite, pupil dilation, and a loss of peripheral vision.

    Pancreas

    The pancreas is a long, slender organ, most of which is located posterior to the bottom half of the stomach (see Figure 20.9). Although it is primarily an exocrine gland, secreting a variety of digestive enzymes, the pancreas has an endocrine function. Its pancreatic islets—clusters of cells formerly known as the islets of Langerhans—secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide (PP).

    Figure 20.9 Pancreas. The pancreatic exocrine function involves the acinar cells secreting digestive enzymes that are transported into the small intestine by the pancreatic duct. Its endocrine function involves the secretion of insulin (produced by beta cells) and glucagon (produced by alpha cells) within the pancreatic islets. These two hormones regulate the rate of glucose metabolism in the body. The micrograph reveals pancreatic islets. LM × 760. (Micrograph provided by the Regents of University of Michigan Medical School © 2012). From Betts, et al., 2013. Licensed under CC BY 4.0. [Image description.]

    Cells and Secretions of the Pancreatic Islets

    The pancreatic islets each contain four varieties of cells:

    • The alpha cell produces the hormone glucagon and makes up approximately 20 percent of each islet. Glucagon plays an important role in blood glucose regulation; low blood glucose levels stimulate its release.
    • The beta cell produces the hormone insulin and makes up approximately 75 percent of each islet. Elevated blood glucose levels stimulate the release of insulin.
    • The delta cell accounts for four percent of the islet cells and secretes the peptide hormone somatostatin. Recall that somatostatin is also released by the hypothalamus (as GHIH), and the stomach and intestines also secrete it. An inhibiting hormone, pancreatic somatostatin inhibits the release of both glucagon and insulin.
    • The PP cell accounts for about one percent of islet cells and secretes the pancreatic polypeptide hormone. It is thought to play a role in appetite, as well as in the regulation of pancreatic exocrine and endocrine secretions. Pancreatic polypeptide released following a meal may reduce further food consumption; however, it is also released in response to fasting.

    Regulation of Blood Glucose Levels by Insulin and Glucagon

    Glucose is required for cellular respiration and is the preferred fuel for all body cells. The body derives glucose from the breakdown of the carbohydrate-containing foods and drinks we consume. Glucose not immediately taken up by cells for fuel can be stored by the liver and muscles as glycogen, or converted to triglycerides and stored in the adipose tissue. Hormones regulate both the storage and the utilization of glucose as required. Receptors located in the pancreas sense blood glucose levels, and subsequently the pancreatic cells secrete glucagon or insulin to maintain normal levels.

    Gonadal Glands

    The male testes and female ovaries—which produce the sex cells (sperm and ova) and secrete the gonadal hormones. The roles of the gonadotropins released from the anterior pituitary (FSH and LH) were discussed earlier.

    The primary hormone produced by the male testes is testosterone, a steroid hormone important in the development of the male reproductive system, the maturation of sperm cells, and the development of male secondary sex characteristics such as a deepened voice, body hair, and increased muscle mass. Interestingly, testosterone is also produced in the female ovaries, but at a much reduced level. In addition, the testes produce the peptide hormone inhibin, which inhibits the secretion of FSH from the anterior pituitary gland. FSH stimulates spermatogenesis.

    The primary hormones produced by the ovaries are estrogens, which include estradiol, estriol, and estrone. Estrogens play an important role in a larger number of physiological processes, including the development of the female reproductive system, regulation of the menstrual cycle, the development of female secondary sex characteristics such as increased adipose tissue and the development of breast tissue, and the maintenance of pregnancy. Another significant ovarian hormone is progesterone, which contributes to regulation of the menstrual cycle and is important in preparing the body for pregnancy as well as maintaining pregnancy. In addition, the granulosa cells of the ovarian follicles produce inhibin, which—as in males—inhibits the secretion of FSH. During the initial stages of pregnancy, an organ called the placenta develops within the uterus. The placenta supplies oxygen and nutrients to the fetus, excretes waste products, and produces and secretes estrogens and progesterone. The placenta produces human chorionic gonadotropin (hCG) as well. The hCG hormone promotes progesterone synthesis and reduces the mother’s immune function to protect the fetus from immune rejection. It also secretes human placental lactogen (hPL), which plays a role in preparing the breasts for lactation, and relaxin, which is thought to help soften and widen the pubic symphysis in preparation for childbirth.

    Common Endocrine System Abbreviations

    • Do you recall the term which describes high level of glucose in the blood?
    • Do you recall the neurotransmitter responsible for assisting the response to danger or stress?
    • Suggest what may happen if the adrenal cortex failed to secrete its hormones.

    Diseases and Disorders

    Acromegaly

    A disorder in adults caused when abnormally high levels of GH trigger growth of bones in the face, hands, and feet.

    Addison’s disease

    A rare disorder that causes low blood glucose levels and low blood sodium levels. The signs and symptoms of Addison’s disease are vague and are typical of other disorders as well, making diagnosis difficult. They may include general weakness, abdominal pain, weight loss, nausea, vomiting, sweating, and cravings for salty food (Betts, et al., 2013).

    Cushing’s disease

    A disorder characterized by high blood glucose levels and the accumulation of lipid deposits on the face and neck. It is caused by hypersecretion of cortisol. The most common source of Cushing’s disease is a pituitary tumor that secretes cortisol or ACTH in abnormally high amounts (Betts, et al., 2013).

    Gigantism

    A disorder in children caused when abnormally high levels of GH prompt excessive growth in the body (Betts, et al., 2013).

    Hirsutism

    Hirsuitism is a symptom of an excessive production of androgens causing hair growth in women where they typically do not have hair growth. While some medications may cause the increased androgen production it can also be linked to endocrine disorders such as Polycystic Ovary Syndrome (PCOS), Cushing syndrome and tumours in the ovaries or adrenal glands (Mayo Clinic Staff, 2020).

    Hyperthyroidism

    A condition marked by high levels of thyroid hormones that results in weight loss, profuse sweating, and increased heart rate (Betts, et al., 2013).

    Hypothyroidism

    A condition marked by low levels of thyroid hormones that results in weight gain, cold sensitivity, and reduced mental activity (Betts, et al., 2013).

    Graves Disease

    A condition marked by a disorder of the thyroid gland, resulting in hyperthyroidism (Betts, et al., 2013).

    Diabetes Inspidius

    A condition caused by a lack of or hyposecretion of the antidiuretic hormone (ADH). The condition can also be caused by the failure of the kidneys to respond to ADH (Betts, et al., 2013).

    Diabetes (Mellitus)

    A condition marked by a disorder of the pancreas, resulting in high levels of glucose in the blood (Betts, et al., 2013).

    Medical Terms in Context

    Medical Specialties and Procedures Related to the Endocrine System

    Endocrinology is a specialization in the field of medicine that focuses on the treatment of endocrine system disorders. Endocrinologists—medical doctors who specialize in this field—are experts in treating diseases associated with hormonal systems, ranging from thyroid disease to diabetes. Endocrine surgeons treat endocrine disease through the removal of the affected endocrine gland or tissue. Some patients experience health problems as a result of the normal decline in hormones that can accompany aging. These patients can consult with an endocrinologist to weigh the risks and benefits of hormone replacement therapy intended to boost their natural levels of reproductive hormones. In addition to treating patients, endocrinologists may be involved in research to improve the understanding of endocrine system disorders and develop new treatments for these diseases (Betts, et al., 2013).

    • A thyroid specialist is an endocrinologist whose sub specialty is focused on the treatment and disorders of the thyroid gland such as hypothyroidism (too low secretion) and hyperthyroidism (too high secretion).
    • A diabetes specialist is an endocrinologist whose sub specialty is focused on the treatment of diabetic conditions.

    Procedures

    Thyroid Scan

    This procedure is designed to check the status of the thyroid. In a thyroid scan, a radioactive compound is given and localized in the thyroid gland (Giorgi & Cherney, 2018). To learn more about a thyroid scan visit HealthLine: Thyroid Scan.

    Radioactive iodine uptake

    Thyroid function evaluated by injecting radioactive iodine and then measuring how much is removed from the blood by the thyroid (MedlinePlus, 2020). To learn more about a radioactive iodine update test visit Medline Plus: Radioactive Iodine Uptake.

    Blood Serum Testing

    Blood testing to determine the concentration and the presence of various endocrine hormones in the blood. These tests include the following levels: calcium, cortisol, electrolytes, FSH, GH, glucose, insulin, parathyroid hormones, T3, T4, testosterone, and TSH. All of these can be evaluated with blood serum tests (Betts, et al., 2013).

    Endocrine Surgical Procedures

    Most of the surgeries and procedures performed with the endocrine system involve removal of a gland or an incision into the gland.  Once an endocrine gland is surgically removed, due to a tumor or enlargement, hormone replacement treatment is required. Medication is required to artificially or synthetically replace the hormone produced by the gland and the function it regulates (Betts, et al., 2013).

    Endocrine System Vocabulary

    Autocrine

    Chemical signal that elicits a response in the same cell that secreted it.

    Endocrine gland

    Tissue or organ that secretes hormones into the blood and lymph without ducts such that they may be transported to organs distant from the site of secretion.

    Endocrine system

    Cells, tissues, and organs that secrete hormones as a primary or secondary function and play an integral role in normal bodily processes.

    Epinephrine

    Also known as adrenaline, is a hormone and neurotransmitter and produced by the adrenal glands.

    Exocrine system

    Cells, tissues, and organs that secrete substances directly to target tissues via glandular ducts.

    Histamine

    Involved in the inflammatory response and typically causes itching.

    Hormone

    Secretion of an endocrine organ that travels via the bloodstream or lymphatics to induce a response in target cells or tissues in another part of the body.

    Neurotransmitter

    Chemicals acting as signaling molecules that enable neurotransmission.

    Norepinephrine

    A natural chemical in the body that acts as both a stress hormone and neurotransmitter (a substance that sends signals between nerve cells). It’s released into the blood as a stress hormone when the brain perceives stress.

    Paracrine

    Chemical signal that elicits a response in neighbouring cells; also called paracrine factor.

    Permeability

    Membrane that causes it to allow liquids or gases to pass through it.

    Proliferation

    Rapid increase in numbers.

    Synthesis

    The production of chemical compounds by reaction from simpler materials.

    Test Yourself

    References

    [CrashCourse]. (2015, June 22). Endocrine system, part 1 – glands & hormones: Crash course A&P #23 [Video]. YouTube. https://www.youtube.com/watch?v=eWHH9je2zG4

    [CrashCourse]. (2015, June 29). Endocrine system, part 2 – hormone cascade: Crash course A&P #24 [Video]. YouTube. https://www.youtube.com/watch?v=eWHH9je2zG4

    Giorgi, A., & Cherney, K. (2018). Thyroid scan. Healthline. https://www.healthline.com/health/thyroid-scan

    MedlinePlus. (2020). Radioactive iodine uptake. US National Library of Medicine. https://medlineplus.gov/ency/article/003689.htm

    Shurkin, J.N.(2013, August 2). Trouble sleeping? Go camping: Artificial light sources can negatively affect circadian rhythms, scientists say. Scientific American. https://www.scientificamerican.com/article/trouble-sleeping-go-campi/

    [TravelersDefense]. (2009, July 28). What does melatonin do? Melatonin use info [Video]. YouTube. https://www.youtube.com/watch?v=EUyBDGgsk_I

    Image Descriptions

    Figure 20.1 image description: This photo shows a young girl reaching for an orange leaf on an oak tree. She is on a walkway near a creek. The opposite shore is a deep slope covered with more trees in autumn colors. [Return to Figure 20.1].

    Figure 20.2 image description: This diagram shows the endocrine glands and cells that are located throughout the body. The endocrine system organs include the pineal gland and pituitary gland in the brain. The pituitary is located on the anterior side of the thalamus while the pineal gland is located on the posterior side of the thalamus. The thyroid gland is a butterfly-shaped gland that wraps around the trachea within the neck. Four small, disc-shaped parathyroid glands are embedded into the posterior side of the thyroid. The adrenal glands are located on top of the kidneys. The pancreas is located at the center of the abdomen. In females, the two ovaries are connected to the uterus by two long, curved, tubes in the pelvic region. In males, the two testes are located in the scrotum below the penis. [Return to Figure 20.2].

    Figure 20.3 image description: This diagram shows a negative feedback loop using the example of glucocorticoid regulation in the blood. Step 1 in the cycle is when an imbalance occurs. The hypothalamus perceives low blood concentrations of glucocorticoids in the blood. This is illustrated by there being only 5 glucocorticoids floating in a cross section of an artery. Step 2 in the cycle is hormone release, where the hypothalamus releases corticotropin-releasing hormone (CRH). Step 3 is labeled correction. Here, the CRH release starts a hormone cascade that triggers the adrenal gland to release glucocorticoid into the blood. This allows the blood concentration of glucocorticoid to increase, as illustrated by 8 glucocorticoid molecules now being present in the cross section of the artery. Step 4 is labeled negative feedback. Here, the hypothalamus perceives normal concentrations of glucocorticoids in the blood and stops releasing CRH. This brings blood glucocorticoid levels back to homeostasis. [Return to Figure 20.3].

    Figure 20.4 image description: This illustration zooms in on the hypothalamus and the attached pituitary gland. The anterior pituitary is highlighted. Three neurosecretory cells are secreting hormones into a web-like network of arteries within the infundibulum. The artery net is labeled the primary capillary plexus of the hypophyseal portal system. The superior hypophysel artery enters the primary capillary plexus from outside of the infundibulum. The hypophyseal portal vein runs down from the primary capillary plexus, through the infundibulum, and connects to the secondary capillary plexus of the hypophyseal portal system. The secondary capillary plexus is located within the anterior pituitary. The hormones released from the neurosecretory cells of the hypothalamus travel through the primary capillary plexus, down the hypophyseal portal vein, and into the secondary capillary plexus. There, the hypothalamus hormones stimulate the anterior pituitary to release its hormones. The anterior pituitary hormones leave the primary capillary plexus from a single vein at the bottom of the anterior lobe. [Return to Figure 20.4].

    Figure 20.5 image description: This flow chart illustrates the hormone cascade that stimulates human growth. In step 1, the hypothalamus releases growth hormone-releasing hormone (GHRH). GHRH travels into the primary capillary plexus of the anterior pituitary, where it stimulates the anterior pituitary to release growth hormone (GH). The release of growth hormone causes three types of effects. In the glucose-sparing effect, GH stimulates adipose cells to break down stored fat, fueling the growth effects (discussed next). The target cells for the glucose-sparing effects are adipose cells. In the growth effects, GH increases the uptake of amino acids from the blood and enhances cellular proliferation while also reducing apoptosis. The target cells for the growth effects are bone cells, muscle cells, nervous system cells, and immune system cells. In the diabetogenic effect, GH stimulates the liver to break down glycogen into glucose, fueling the growth effects. The liver also releases IGF in response to GH. The IGF further stimulates the growth effects but also negatively feeds back to the hypothalamus. When high IGF one levels are perceived by the hypothalamus, it releases growth hormone inhibiting hormone (GHIH). GHIH inhibits GH release by the anterior pituitary. [Return to Figure 20.5].

    Figure 20.6 image description: This illustration zooms in on the hypothalamus and the attached pituitary gland. The posterior pituitary is highlighted. Two nuclei in the hypothalamus contain neurosecretory cells that release different hormones. The neurosecretory cells of the paraventricular nucleus release oxytocin (OT) while the neurosecretory cells of the supraoptic nucleus release anti-diuretic hormone (ADH). The neurosecretory cells stretch down the infundibulum into the posterior pituitary. The tube-like extensions of the neurosecretory cells within the infundibulum are labeled the hypothalamophypophyseal tracts. These tracts connect with a web-like network of blood vessels in the posterior pituitary called the capillary plexus. From the capillary plexus, the posterior pituitary secretes the OT or ADH into a single vein that exits the pituitary. [Return to Figure 20.6].

    Figure 20.7 image description: Part A of this figure is a diagram of the anterior view of the thyroid gland. The thyroid gland is a butterfly-shaped gland wrapping around the trachea. It narrows at its center, just under the thyroid cartilage of the larynx. This narrow area is called the isthmus of the thyroid. Two large arteries, the common carotid arteries, run parallel to the trachea on the outer border of the thyroid. A small artery enters the superior edge of the thyroid, near the isthmus, and branches throughout the two “wings” of the thyroid. Part B of this figure is a posterior view of the thyroid. The posterior view shows that the thyroid does not completely wrap around the posterior of the trachea. The posterior sides of the thyroid wings can be seen protruding from under the cricoid cartilage of the larynx. The posterior sides of the thyroid “wings” each contain two small, disc-shaped parathyroid glands embedded in the thyroid tissue. Within each wing, one disc is located superior to the other. These are labeled the left and right parathyroid glands. Just under the inferior parathyroid glands are two arteries that bring blood to the thyroid from the left and right subclavian arteries. Part C of this figure is a micrograph of thyroid tissue. The thyroid follicle cells are cuboidal epithelial cells. These cells form a ring around irregular-shaped cavities called follicles. The follicles contain light colored colloid. A larger parafollicular cell is embedded between two of the follicular cells near the edge of a follicle. [Return to Figure 20.7].

    Figure 20.8 image description: This diagram shows the left adrenal gland located atop the left kidney. The gland is composed of an outer cortex and an inner medulla all surrounded by a connective tissue capsule. The cortex can be subdivided into additional zones, all of which produce different types of hormones. The outermost layer is the zona glomerulosa, which releases mineralcorticoids, such as aldosterone, that regulate mineral balance. Underneath this layer is the zona fasciculate, which releases glucocorticoids, such as cortisol, corticosterone and cortisone, that regulate glucose metabolism. Underneath this layer is the zona reticularis, which releases androgens, such as dehydroepiandrosterone, that stimulate masculinization. Below this layer is the adrenal medulla, which releases stress hormones, such as epinephrine and norepinephrine, that stimulate the symphathetic ANS. [Return to Figure 20.8].

    Figure 20.9 image description: This diagram shows the anatomy of the pancreas. The left, larger side of the pancreas is seated within the curve of the duodenum of the small intestine. The smaller, rightmost tip of the pancreas is located near the spleen. The splenic artery is seen travelling to the spleen, however, it has several branches connecting to the pancreas. An interior view of the pancreas shows that the pancreatic duct is a large tube running through the center of the pancreas. It branches throughout its length in to several horseshoe- shaped pockets of acinar cells. These cells secrete digestive enzymes, which travel down the bile duct and into the small intestine. There are also small pancreatic islets scattered throughout the pancreas. The pancreatic islets secrete the pancreatic hormones insulin and glucagon into the splenic artery. An inset micrograph shows that the pancreatic islets are small discs of tissue consisting of a thin, outer ring called the exocrine acinus, a thicker, inner ring of beta cells and a central circle of alpha cells. [Return to Figure 20.9].

    Endocrine System Diagram, Parts And Functions, For Kids

    The endocrine system includes glands that produce hormones in the body. Hormones coordinate complex body processes, such as metabolism and growth. They also play a role in the immune system functions and behavior of a person. Thus, the endocrine system controls several bodily functions through the regulation of hormones.

    Read this post to know more about the functions and parts of the endocrine system and various endocrine disorders, their symptoms, and how to prevent them.

    What Does The Endocrine System Do?

    The main role of the endocrine system is to secrete hormones into the bloodstream. These hormones are secreted in very small amounts in order to produce an effect on specific cells or systems in the body. It is all about balance – low levels as well as high level of a hormone lead to disease. These hormones reach different body parts to regulate various functions. These functions include (1):

    • Regulate metabolism
    • Control growth and development
    • Reproduction
    • Control the mood
    • Functions of various organs
    • Regulate sleep patterns

    What Are The Parts Of The Endocrine System?

    The major glands in the endocrine system are (2):

    1. Hypothalamus

    Hypothalamus is located in the lower part of the brain and connects the endocrine system with the central nervous system through the pituitary gland. The nerve cells of the hypothalamus control the hormone release from the pituitary gland, which regulates the other endocrine glands’ hormone secretions.

    The hypothalamus signals the production of pituitary hormones, based on the brain’s sensations, such as thirst, hunger, temperature, light exposure, and sleep. The following are the hormones released by the hypothalamus (3).

    • Thyrotropin-releasing hormone (TRH) reaches the pituitary gland and stimulates the release of thyroid-stimulating hormone (TSH) and prolactin (PRL).
    • Gonadotropin-releasing hormone (GnRH) primarily stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The secondary effects are increased release of estrogen and progesterone in females and testosterone in males.
    • Growth hormone-releasing hormone (GHRH) signals the pituitary gland to release growth hormone (GH).
    • Corticotropin-releasing hormone (CRH) signals pituitary cells to release corticotropin, also called adrenocorticotropic hormone (ACTH), to stimulate the release of adrenal hormones. This is also secreted by the placenta during pregnancy to prevent a maternal immune system attack on the fetus and determine the duration of gestation.
    • Somatostatin is an inhibitory hormone that inhibits the release of growth hormone (GH) and thyroid-stimulating hormone (TSH) from the pituitary gland. This is also secreted in the pancreas and intestine, where it inhibits various digestive hormones.
    • Dopamine is a hormone and neurotransmitter that inhibits the secretion of prolactin (PRL) from the pituitary gland. This also plays a role in activating brain reward centers and modulating the brain’s motor control centers. Dopamine secreting cells are also seen in other parts of the body that act locally.

    2. Pituitary gland

    The pituitary gland is located at the base of the brain. This pea-sized gland is the master gland of the endocrine system. Based on the hypothalamic signals, the pituitary gland sends inhibitory or stimulatory hormones to the other endocrine glands.

    The following hormones are secreted by the anterior part of the pituitary gland (4).

    • Growth hormone (somatotropin) stimulates growth, development, and metabolism of the body. It controls cell regeneration and also plays vital roles in the utilization of nutrients and minerals.
    • Prolactin stimulates milk production in lactating women.
    • Thyrotropin (thyroid-stimulating hormone) controls the production of thyroid hormones.
    • Corticotropin (Adrenocorticotrophin or ACTH) stimulates the production of the adrenal hormones.
    • Gonadotropins include FSH and LH. These hormones stimulate the production of reproductive cells and reproductive hormones, such as testosterone in males and estrogen in females.

    The following hormones are directly released into the posterior pituitary from the hypothalamus.

    • Vasopressin, also known as arginine vasopressin (AVP) or antidiuretic hormone (ADH), regulates osmotic balance, blood pressure, sodium hemostasis, and kidney functions in humans. Vasopressin acts on the kidneys to maintain water balance in the body.
    • Oxytocin is a bonding hormone that enhances bonding, such as in the case of male and female or mother and newborn. This hormone increases a person’s trust in other people. Oxytocin also causes smooth muscle contractions, such as the uterus’ contraction during birth and release of milk when the baby suckles.

    The pituitary also secretes hormones called endorphins and enkephalins, which block pain signals from the brainstem and spinal cord. Endorphins also play a role in immune system responses of the body.

    Beta-melanocyte-stimulating hormone (melanotropin) stimulates melanin production by melanocytes in the skin and suppresses appetite by acting on the hypothalamus.

    3. Thyroid gland

    The thyroid gland is a butterfly or a bow-shaped gland located at the front of the lower neck. Triiodothyronine (T3) and thyroxine (T4) are hormones produced by the thyroid gland. Thyroid hormones play an essential role in metabolism, which is the energy production rate from food by body cells. High levels of thyroid hormones cause faster metabolism.

    Parafollicular cells or C cells of the thyroid gland make a hormone called calcitonin, which controls calcium and phosphorus’s metabolism in the body. Calcitonin is also produced in other parts of the body, such as in the lungs and intestines. This hormone prevents osteoclast activity from digesting and releasing bone minerals (calcium and phosphorus) into the bloodstream and losing them through kidney excretion.

    Thyroid hormones play a significant role in the growth and development of children. These hormones also influence general functions, such as body temperature and bone growth.

    4. Parathyroid gland

    Parathyroids are four small glands attached to the thyroid gland. They secrete parathyroid hormone (PTH), which regulates the levels of calcium in our body.

    5. Adrenal glands

    Adrenal glands, also called suprarenal glands, are triangle-shaped glands on top of the kidneys. These glands make several hormones from its outer part called the adrenal cortex, and the inner part called the adrenal medulla.

    The following hormones are produced by the adrenal cortex.

    • Cortisol (glucocorticoid hormone) controls the use of carbohydrates, proteins, and fats by the body. It regulates blood pressure, blood glucose, and decreases bone formation. Cortisol also helps in the suppression of inflammation in the body.
    • Aldosterone (mineralocorticoid hormone) regulates blood pressure and blood pH levels. The hormone regulates electrolytes, such as sodium and potassium, in the blood to maintain blood pH.
    • Androgenic steroids and DHEA help in the production of sex hormones.

    Adrenaline (epinephrine) and noradrenaline (norepinephrine) are hormones produced by the adrenal medulla. These play a crucial role in stress response and regulate blood pressure and heart rate. They also function as neurotransmitters.

    6. Pineal gland

    The pineal gland, also called the pineal body, is a tiny pea-shaped endocrine gland located in the middle of the brain. It secretes the hormone melatonin that regulates the circadian rhythm (sleep pattern) in humans.

    7. Reproductive glands

    Reproductive glands are also called sex glands or gonads. These are mixed glands since they produce gametes (reproductive cells) and reproductive (sex) hormones. The male gonad produces hormones called androgens (male sex hormone). Testosterone is an important androgen that controls pubertal changes, such as growth and development of secondary sexual characteristics, including facial hair, pubic hair, and voice change.

    Ovaries are female gonads located on either side of the uterus in the pelvis. Female hormones, such as estrogen and progesterone, are secreted by the ovaries. Estrogen regulates the secondary sexual characteristics in females, such as breast growth, fat deposit in the hip and thighs, and the growth spurt during puberty. Progesterone and estrogen together regulate the menstrual cycles and play a key role in pregnancy.

    8. Pancreatic islets

    The pancreas is a part of both the endocrine and digestive systems. The exocrine cells of the pancreas have digestive functions, whereas the pancreatic islet (islets of Langerhans) has endocrine functions.

    The main hormones secreted by islets of Langerhans are:

    • Insulin is produced by the pancreas’ beta cells. This hormone is involved in the metabolism of carbohydrates, proteins, and fat in the body. Insulin is made when blood sugar levels are high. It promotes glucose (sugar) absorption from the blood to the liver, fat and skeletal muscles.
    • Glucagon is produced by alpha cells of pancreatic islets when blood glucose levels are low. This converts glycogen (glucose storage in the liver and muscles) and releases glucose into the bloodstream.

    Somatostatin (growth hormone-inhibiting hormone), ghrelin (the hunger hormone), and pancreatic polypeptide (PP) are other hormones produced by the endocrine cells of the pancreas.

    Problems Of The Endocrine System In Children

    Too much or too little of any hormone can cause imbalances in the body functions. Injuries, autoimmune attacks, tumors, and infections are some of the conditions that could cause endocrine disorders. These disorders could also be a result of genetic factors or acquired factors, such as physical inactivity and an unhealthy diet.

    Dysfunction of the hypothalamus or pituitary gland could impact overall endocrine functions in the body. Clinical manifestations may vary depending on the affected gland and the level of hormones made by it.

    Although there are several endocrine disorders, children are most vulnerable to the following ones (5).

    Signs And Symptoms Of Endocrine Problems

    The following signs and symptoms could indicate endocrine problems in children (5).

    • Frequent urination
    • Constant weakness or lethargy
    • Excess weight gain or loss
    • Frequent nausea and belly pain
    • Increased thirst
    • Increased sweating
    • Tremors (involuntary muscle contractions)
    • Frequent constipation
    • Delay in growth and development

    Injuries or diseases of endocrine glands can cause various health conditions. Endocrine disorders due to reduction or lack of hormones require hormone replacement therapy (HRT) to relieve insufficiency symptoms. Excess secretion of hormones also requires medical treatment since this also affects the normal functioning of the body.

    You may consult a pediatric endocrinologist if your child has symptoms of endocrine disorders.

    How Can Chemicals Affect The Endocrine System?

    Endocrine disruptors are chemicals that may mimic or interfere with human hormones. These chemicals can cause growth, reproductive, immune system, or brain issues in children. Endocrine-disrupting chemicals are found in several common products of daily use or generated during some activities (6).

    Endocrine disruptors Sources
    Bisphenol A (BPA)
    • Food storage containers
    • Polycarbonate plastics
    • Epoxy resins
    Dioxins
    • Herbicides
    • Paper bleaching
    • Waste burning
    • Wildfires
    Perchlorate
    • Pharmaceuticals
    • Drinking water
    • Fireworks
    Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS)
    • Firefighting foams
    • Textile coatings
    • Paper
    • Non-stick pan
    Triclosan
    • Anti-microbial products
    • Personal care products, such as liquid body wash
    Polychlorinated biphenyls (PCB)
    • Plasticizers
    • Heat transfer fluids
    • Hydraulic fluids
    • Lubricants
    • Electric equipment, such as transformers
    Polybrominated diphenyl ethers (PBDE)
    Phytoestrogens (genistein and daidzein)
    • Naturally found in some plants, such as soybean
    • Plant-based products, such as soy milk and tofu
    Phthalates
    • Food packaging
    • Cosmetics
    • Toys
    • Medical devices

    Children can come in contact with these chemicals through air, water, skin, or food. Even low doses of these chemicals are unsafe since it may cause biological effects. Avoid pollutants and keep chemicals away from the child’s reach. It is impossible to avoid all these listed products/ compounds. Most people get exposed to them on a regular basis. This does not mean that all contact leads to endocrine disruption, but obvious/ high incidence exposures should be limited where possible. Pick non-toxic and child-safe toys, clothes, and other related products.

    Tips For Healthy Endocrine System In Children

    The following measures might help prevent endocrine problems in children.

    • Regular medical follow-ups may help to identify hormonal imbalances before the symptoms develop if there is a family history or any suspicion of imbalance.
    • Early screening for children with a positive family history of endocrine issues, such as hypo or hyperthyroidism, and diabetes.

    Lack or excess of hormones can interfere with the normal growth and development of the children. Seek medical care if you notice symptoms of hormonal imbalances in your child. Early hormone therapies may have better outcomes than delayed interventions. A healthy diet and regular exercise can help avoid some hormonal imbalances.

    References:
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    Endocrine System Anatomy and Physiology

    Our body cells have dynamic adventures on microscopic levels all the time. For instance, when insulin molecules, carried passively along in the blood leave the blood and bind tightly to protein receptors of nearby cells, the response it dramatic: blood borne glucose molecules begin to disappear into the cells, and cellular activity accelerates.

    Functions of the Endocrine System


    Despite the huge variety of hormones, there are really only two mechanisms by which hormones trigger changes in cells.

    1. Water equilibrium. The endocrine system controls water equilibrium by regulating the solute concentration of the blood.
    2. Growth, metabolism, and tissue maturation. The endocrine system controls the growth of many tissues, like the bone and muscle, and the degree of metabolism of various tissues, which aids in the maintenance of the normal body temperature and normal mental functions. Maturation of tissues, which appears in the development of adult features and adult behavior, are also determined by the endocrine system.
    3. Heart rate and blood pressure management. The endocrine system assists in managing the heart rate and blood pressure and aids in preparing the body for physical motion.
    4. Immune system control. The endocrine system helps regulate the production and functions of immune cells.
    5. Reproductive function controls. The endocrine system regulates the development and the functions of the reproductive systems in males and females.
    6. Uterine contractions and milk release. The endocrine system controls uterine contractions throughout the delivery of the newborn and stimulates milk release from the breasts in lactating females.
    7. Ion management. The endocrine system regulates Na+, K+, and Ca2+ concentrations in the blood.
    8. Blood glucose regulator. The endocrine system controls blood glucose levels and other nutrient levels in the blood.
    9. Direct gene activation. Being lipid-soluble molecules, the steroid hormones can diffuse through plasma membranes of their target cells; once inside, the steroid hormone enters the nucleus and binds to a specific receptor protein there; then, the hormone-receptor complex binds to specific sites on the cell’s DNA, activating certain genes to transcribe messenger RNA; the mRNA then is translated in the cytoplasm, resulting in the synthesis of new proteins.
    10. Second messenger system. Water-soluble, nonsteroidal hormones-protein, and peptide hormones- are unable to enter the target cells, so instead, they bind to receptors situated on the target cell’s plasma membrane and utilize a second messenger system.

    Anatomy of the Endocrine System

    Compared to other organs of the body, the organs of the endocrine system are small and unimpressive, however, functionally the endocrine organs are very impressive, and when their role in maintaining body homeostasis is considered, they are true giants.

    Hypothalamus


    The major endocrine organs of the body include the pituitary, thyroid, parathyroid, adrenal, pineal and thymus glands, the pancreas, and the gonads.

    • Hypothalamus. The hypothalamus, which is part of the nervous system, is also considered as a major endocrine organ because it produces several hormones. It is an important autonomic nervous system and endocrine control center of the brain located inferior to the thalamus.
    • Mixed functions. Although the function of some hormone-producing glands is purely endocrine, the function of others (pancreas and gonads) is mixed- both endocrine and exocrine.

    Pituitary Gland


    The pituitary gland is approximately the size of a pea.

    • Location. The pituitary gland hangs by a stalk from the inferior surface of the hypothalamus of the brain, where it is snugly surrounded by the “Turk’s saddle” of the sphenoid bone.
    • Lobes. It has two functional lobes- the anterior pituitary (glandular tissue) and the posterior pituitary (nervous tissue).

    Hormones of the Anterior Pituitary

    There are several hormones of the anterior pituitary hormones that affect many body organs.

    • Growth hormone (GH). Growth hormone is a general metabolic hormone, however,  its major effects are directed to the growth of skeletal muscles and long bones of the body; it is a protein-sparing and anabolic hormone that causes amino acids to be built into proteins and stimulates most target cells to grow in size and divide.
    • Prolactin (PRL). Prolactin is a protein hormone structurally similar to growth hormone; its only known target in humans is the breast because, after childbirth, it stimulates and maintains milk production by the mother’s breast.
    • Adrenocorticotropic hormone (ACTH). ACTH regulates the endocrine activity of the cortex portion of the adrenal gland.
    • Thyroid-stimulating hormone (TSH). TSH, also called thyrotropin hormone influences the growth and activity of the thyroid gland.
    • Gonadotropic hormones. The gonadotropic hormones regulate the hormonal activity of gonads (ovaries and testes).
    • Follicles-stimulating hormone (FSH). FSH stimulates follicle development in the ovaries; as the follicles mature, they produce estrogen and eggs that are readied for ovulation; in men, FSH stimulates sperm development by the testes.
    • Luteinizing hormone (LH). LH triggers ovulation of an egg from the ovary and causes the ruptured follicle to produce progesterone and some estrogen; in men, LH stimulates testosterone production by the interstitial cells of the testes.

    Hormones of the Posterior Pituitary

    The posterior pituitary is not an endocrine gland in the strict sense because it does not make the peptide hormones it releases, but it simply acts as a storage area for hormones made by hypothalamic neurons.

    • Oxytocin. Oxytocin is released in significant amount only during childbirth and in nursing women; it stimulates powerful contractions of the uterine muscle during labor, during sexual relations, and during breastfeeding and also causes milk ejection (let-down reflex) in a nursing woman.
    • Antidiuretic hormone (ADH). ADH causes the kidneys to reabsorb more water from the forming of urine; as a result, urine volume decreases and blood volume increases; in larger amounts, ADH also increases blood pressure by causing constriction of the arterioles, so it is sometimes referred to as vasopressin.

    Thyroid Gland


    The thyroid gland is a hormone-producing gland that is familiar to most people primarily because many obese individuals blame their overweight condition on their “glands” (thyroid).

    • Location. The thyroid gland is located at the base of the throat, just inferior to the Adam’s apple, where it is easily palpated during a physical examination.
    • Lobes. It is a fairly large gland consisting of two lobes joined by a central mass, or isthmus.
    • Composition. Internally, the thyroid gland is composed of hollow structures called follicles, which store a sticky colloidal material.
    • Types of thyroid hormones. Thyroid hormone often referred to as the body’s major metabolic hormone, is actually two active, iodine-containing hormones, thyroxine or T4, and triiodothyronine or T3.
    • Thyroxine. Thyroxine is the major hormone secreted by the thyroid follicles.
    • Triiodothyronine. Most triiodothyronine is formed at the target tissues by conversion of the thyroxine to triiodothyronine.
    • Function. Thyroid hormone controls the rate at which glucose is “burned” oxidized, and converted to body heat and chemical energy; it is also important for normal tissue growth and development.
    • Calcitonin. Calcitonin decreases blood calcium levels by causing calcium to be deposited in the bones; calcitonin is made by the so-called parafollicular cells found in the connective tissues between the follicles.

    Parathyroid Glands


    The parathyroid glands are mostly tiny masses of glandular tissue.

    • Location. The parathyroid glands are located on the posterior surface of the thyroid gland.
    • Parathormone. The parathyroids secrete parathyroid hormone (PTH) or parathormone, which is the most important regulator of calcium ion homeostasis of the blood; PTH is a hypercalcemic hormone (that is, it acts to increase blood levels of calcium), whereas calcitonin is a hypocalcemic hormone.; PTH also stimulates the kidneys and intestines to absorb more calcium.

    Adrenal Glands


    Although the adrenal gland looks like a single organ, it is structurally and functionally two endocrine organs in one.

    Hormones of the Adrenal Cortex

    The adrenal cortex produces three major groups of steroid hormones, which are collectively called corticosteroids– mineralocorticoids, glucocorticoids, and sex hormones.

    • Mineralocorticoids. The mineralocorticoids, primarily aldosterone, are produced by the outermost adrenal cortex cell layer; mineralocorticoids are important in regulating the mineral (or salt) content of the blood, particularly the concentrations of sodium and potassium ions and they also help in regulating the water and electrolyte balance in the body.
    • Renin. Renin, am enzyme produced by the kidneys when the blood pressure drops, also cause the release of aldosterone by triggering a series of reactions that form angiotensin II, a potent stimulator of aldosterone release.
    • Atrial natriuretic peptide (ANP). ANP prevents aldosterone release, its goal being to reduce blood volume and blood pressure.
    • Glucocorticoids. The middle cortical layer mainly produces glucocorticoids, which include cortisone and cortisol; glucocorticoids promote normal cell metabolism and help the body to resist long-term stressors, primarily by increasing blood glucose levels, thus it is said to be a hyperglycemic hormone; it also reduce pain and inflammation by inhibiting some pain-causing molecules called prostaglandins.
    • Sex hormones. Both male and female sex hormones are produced by the adrenal cortex throughout life in relatively small amounts; although the bulk of sex hormones produced by the innermost cortex layer are androgens (male sex hormones), some estrogens (female sex hormones), are also formed.

    Hormones of the Adrenal Medulla

    The adrenal medulla, like the posterior pituitary, develops from a knot of nervous tissue.

    • Catecholamines. When the medulla is stimulated by sympathetic nervous system neurons, its cells release two similar hormones, epinephrine, also called adrenaline, and norepinephrine (noradrenaline), into the bloodstream; collectively, these hormones are referred to as catecholamines.
    • Function. Basically, the Catecholamines increase heart rate, blood pressure, and blood glucose levels and dilate the small passageways of the lungs; the catecholamines of the adrenal medulla prepare the body to cope with a brief or short-term stressful situation and cause the so-called alarm stage of the stress response.

    Pancreatic Islets


    The pancreas, located close to the stomach in the abdominal cavity, is a mixed gland.

    • Islets of Langerhans.The islets of Langerhans also called pancreatic islets, are little masses of hormone-producing tissue that are scattered among the enzyme-producing acinar tissue of the pancreas.
    • Hormones. Two important hormones produced by the islet cells are insulin and glucagon.
    • Islet cells. Islet cells act as fuel sensors, secreting insulin and glucagon appropriately during fed and fasting states.
    • Beta cells. High levels of glucose in the blood stimulate the release of insulin from the beta cells of the islets.
    • Alpha cells. Glucagon’s release by the alpha cells of the islets is stimulated by low blood glucose levels.
    • Insulin. Insulin acts on just about all the body cells and increases their ability to transport glucose across their plasma membranes; because insulin sweeps glucose out of the blood, its effect is said to be hypoglycemic.
    • Glucagon. Glucagon acts as an antagonist of insulin; that is, it helps to regulate blood glucose levels but in a way opposite that of insulin; its action is basically hyperglycemic and its primary target organ is the liver, which it stimulates to break down stored glycogen into glucose and release the glucose into the blood.

    Pineal Gland


    The pineal gland, also called the pineal body, is a small cone-shaped gland.

    • Location. The pineal gland hangs from the roof of the third ventricle of the brain.
    • Melatonin. Melatonin is the only hormone that appears to be secreted in substantial amounts by the pineal gland; the levels of melatonin rise and fall during the course of the day and night; peak levels occur at night and make us drowsy as melatonin is believed to be the “sleep trigger” that plays an important role in establishing the body’s day-night cycle.

    Thymus Gland


    The thymus gland is large in infants and children and decreases in size throughout adulthood.

    • Location. The thymus gland is located in the upper thorax, posterior to the sternum.
    • Thymosin. The thymus produces a hormone called thymosin and others that appear to be essential for normal development of a special group of white blood cells (T-lymphocytes, or T cells) and the immune response.

    Gonads


    Main Article: Female Reproductive System and Male Reproductive System

    The female and male gonads produce sex hormones that are identical to those produced by adrenal cortex cells; the major difference are the source and relative amount produced.

    Hormones of the Ovaries

    The female gonads or ovaries are a pair of almond-sized organs.

    • Location. The female gonads are located in the pelvic cavity.
    • Steroid hormones. Besides producing female sex cells, ovaries produce two groups of steroid hormones, estrogen, and progesterone.
    • Estrogen. Alone, the estrogens are responsible for the development of sex characteristics in women at puberty; acting with progesterone, estrogens promote breast development and cyclic changes in the uterine lining (menstrual cycle).
    • Progesterone. Progesterone acts with estrogen to bring about the menstrual cycle; during pregnancy, it quiets the muscles of the uterus so that an implanted embryo will not be aborted and helps prepare breast tissue for lactation.

    Hormones of the Testes

    The testes of the male are paired oval organs in a sac.

    • Location. The testes are suspended in a sac, the scrotum, outside the pelvic cavity.
    • Male sex hormones. In addition to male sex cells, or sperm, the testes also produce male sex hormones, or androgens, of which testosterone is the most important.
    • Testosterone. At puberty, testosterone promotes the growth and maturation of the reproductive system organs to prepare the young man for reproduction; it also causes the male’s secondary sex characteristics to appear and stimulates male sex drive; Testosterone is also necessary for the continuous production of sperm.

    Other Hormone-Producing Tissues and Organs

    Besides the major endocrine organs, pockets of hormone-producing cells are found in fatty tissue and in the walls of the small intestine, stomach, kidneys, and heart- organs whose chief functions have little to do with hormone production.

    Placenta


    The placenta is a remarkable organ formed temporarily in the uterus of pregnant women.

    • Function. In addition to its roles as the respiratory, excretory, and nutrition delivery systems for the fetus, it also produces several proteins and steroid hormones that help to maintain the pregnancy and pave the way for delivery of the baby.
    • Human chorionic gonadotropin. During very early pregnancy, a hormone called human chorionic gonadotropin (hCG) is produced by the developing embryo and then by the fetal part of the placenta; hCG stimulates the ovaries to continue producing estrogen and progesterone so that the lining of the uterus is not sloughed off in the menses.
    • Human placental lactogen (hPL). hPL works cooperatively with estrogen and progesterone in preparing the breasts for lactation.
    • Relaxin. Relaxin, another placental hormone, causes the mother’s pelvic ligaments and the pubic symphysis to relax and become more flexible, which eases birth passage.

    Physiology of the Endocrine System

    Although hormones have widespread effects, the major processes they control are reproduction, growth, and development; mobilizing the body’s defenses against stressors; maintaining electrolyte, water, and nutrient balance of the blood; and regulating cellular metabolism and energy balance.

    The Chemistry of Hormones


    The key to the incredible power of the endocrine glands is the hormones they produce and secrete.

    • Hormones. Hormones may be defined as chemical substances that are secreted by endocrine cells into the extracellular fluids and regulate the metabolic activity of other cells in the body.
    • Classification. Although many different hormones are produced, nearly all of them can be classified chemically as either amino acid-based molecules (including proteins, peptides, and amines) or steroids.
    • Steroid hormones. Steroid hormones (made from cholesterol) include the sex hormones made by the gonads and hormones produced by the adrenal cortex.
    • Amino acid-based hormones. All the others are nonsteroidal amino acid derivatives.

    Mechanisms of Hormone Action


    Although the blood-borne hormones circulate to all the organs of the body, a given hormone affects only certain tissue cells or organs.

    • Target cells. For a target cell to respond to the hormone, specific protein receptors must be present on its plasma membrane or in its interior to which that hormone can attach; only when this binding occurs can the hormone influence the workings of cells.
    • Function of hormones. The hormones bring about their effects on, the body cells primarily by altering cellular activity- that is, by increasing or decreasing the rate of a normal, or usual, metabolic process rather than stimulating a new one.
    • Changes in hormone binding. The precise changes that follow hormone binding depend on the specific hormone and the target cell type, but typically one or more of the following occurs:
    1. Changes in plasma membrane permeability or electrical state.
    2. Synthesis of protein or certain regulatory molecules (such as enzymes) in the cell.’
    3. Activation or inactivation of enzymes.
    4. Stimulation of mitosis.
    5. Promotion of secretory activity.

    Control of Hormone Release


    What prompts the endocrine glands to release or not release their hormones?

    • Negative feedback mechanisms. Negative feedback mechanisms are the chief means of regulating blood levels of nearly all hormones.
    • Endocrine gland stimuli. The stimuli that activate the endocrine organs fall into three major categories- hormonal, humoral, and neural.
    • Hormonal stimuli. The most common stimulus is a hormonal stimulus, in which the endocrine organs are prodded into action by other hormones; for example, hypothalamic hormones stimulate the anterior pituitary gland to secrete its hormones, and many anterior pituitary hormones stimulate other endocrine organs to release their hormones into the blood.
    • Humoral stimuli. Changing blood levels of certain ions and nutrients may also stimulate hormone release, and this is referred to as humoral stimuli; for example, the release of parathyroid hormone (PTH) by cells of the parathyroid glands is prompted by decreasing blood calcium levels.
    • Neural stimuli. In isolated cases, nerve fibers stimulate hormone release, and the target cells are said to respond to neural stimuli; a classic example is sympathetic nervous system stimulation of the adrenal medulla to release norepinephrine and epinephrine during periods of stress.

    Practice Quiz: Endocrine System Anatomy and Physiology


    Here’s a 10-item quiz about the study guide. Please visit our nursing test bank page for more NCLEX practice questions.

    1. The following are the functions of the endocrine system, except?

    A. Regulates immune system
    B. Controls reproductive function
    C. Regulate heart rate and blood pressure
    D. Water balance
    E. Direct blood flow

    1. Answer: E. Direct blood flow

    • E. This is a function of the peripheral circulation wherein the system directs blood to tissues when increased blood flow is required to maintain homeostasis.
    • A: The endocrine system helps control the production and function of the immune cells.
    • B: The endocrine system helps controls the development and functions of the reproductive systems in males and females.
    • C: The endocrine system helps regulate heart rate and blood pressure and helps prepare the body for physical exertion.
    • D: The endocrine system regulates water balance by controlling the solute concentration of the blood.

    2. The primary function of T3 and T4 is to:

    A. Reduce blood glucose levels
    B. Release calcitonin
    C. Regulate bone growth
    D. Increase metabolic rate

    2. Answer: D. Increase metabolic rate

    • D: T3 and T4 are released throughout the body to direct the body’s metabolism. They stimulate all cells within the body to increase metabolic rate.
    • A: Insulin lowers blood glucose levels, and promotes the formation of glycogen.
    • B: Calcitonin is a hormone that the C-cells in the thyroid gland produces and release.  It opposes the action of the parathyroid hormone, helping to regulate the blood’s calcium and phosphate levels.
    • C: Body growth is controlled by growth hormone (GH), produced by the anterior pituitary gland.

    3. Antidiuretic hormone and oxytocin are stored and released by the:

    A. Adrenal cortex
    B. Posterior pituitary gland
    C. Thyroid gland
    D. Pineal gland

    3. Answer: B. Posterior pituitary gland

    • B: The posterior pituitary gland releases two hormones (antidiuretic hormone and oxytocin).
    • A: The two major hormones produced by the adrenal cortex are the mineralocorticoids and the glucocorticoids.
    • C: The Thyroid gland is involved in the production of the hormones T3 (triiodothyronine) and T4 (thyroxine).
    • D: The main hormone produced and secreted by the pineal gland is melatonin.

    4. Which hormone stimulates the male testes to produce sperm and stimulates the development of the follicle in the female on a monthly cycle.

    A. Luteinizing hormone
    B. Somatostatin
    C. Follicle-stimulating hormone
    D. Thymosin

    4. Answer: C. Follicle-stimulating hormone

    • C: Follicle-stimulating hormone stimulates the growth of ovarian follicles in the ovary in females and acts on the Sertoli cells of the testes to stimulate sperm production (spermatogenesis) in males.
    • A: Luteinizing hormone. For women, the hormone stimulates the ovaries to produce oestradiol. For men, it stimulates the production of testosterone from Leydig cells in the testes
    • B: The primary function of somatostatin is to inhibit the production of other hormones and also prevent the unnatural rapid reproduction of cells (such as those in tumors).
    • D: Thymosin enhances the ability of the immune system to function.

    5. A client with a history of hypertension is admitted due to primary hyperaldosteronism. This diagnosis indicates that the client’s hypertension is caused by excessive hormone secretion from which gland?

    A. Pancreas
    B. Adrenal cortex
    C. Thymus gland
    D. Adrenal medulla

    5. Answer: B. Adrenal cortex

    • B: Excessive aldosterone secretion in the adrenal cortex is responsible for the client’s hypertension.
    • A: Pancreas secretes hormones involved in glucose metabolism.
    • C: Thymus gland secretes thymosin, which stimulates the development of disease-fighting T cells.
    • D: Adrenal medulla secretes the catecholamines (epinephrine and norepinephrine).

    6. The mineralocorticoids produced by the adrenal glands are produced within the?

    A. Parafollicular cells
    B. Zona reticularis
    C. Zona glomerulosa
    D. Zona fasciculata

    6. Answer: C. Zona glomerulosa

    • C: The zona glomerulosa is responsible for synthesis of aldosterone as well as some other corticosteroids such as glucocorticoid.
    • A: Calcitonin is produced by the parafollicular cells found in the connective tissues between the follicles.
    • B&D: Zona reticularis acts in collaboration with the Zona fasciculata and is primarily involved in the synthesis as well as secretion of different sex hormones that work as a substitute for gonadal hormones.

    7. Which of the following glands is both an endocrine gland and an exocrine gland, except?

    A. Pancreas
    B. Kidney
    C. Gonads
    D. Pituitary gland

    7. Answer: D. Pituitary gland

    • D: Pituitary gland has only an endocrine component.
    • A, B, and C: Endocrine component of glands with both an endocrine and an exocrine function. These include the pancreas, kidney, and gonads.

    8. Which of the following is not true with melatonin?

    A. Melatonin induces heat loss, reduces arousal and related brain activity and delays production of cortisol.
    B. It helps regulate biological rhythms such as sleep and wake cycles.
    C. The secretion of melatonin is inhibited by darkness and triggered by light.
    D. The pineal gland produces and secretes the hormone.

    8. Answer: C. The secretion of melatonin is inhibited by darkness and triggered by light.

    • C: Light exposure resets the circadian rhythm of melatonin and acutely inhibits melatonin synthesis while the secretion of melatonin is triggered by darkness.

    9. Part of the effect of growth hormone is influenced by a group of protein chemical signals called:

    A. Somatomedin-C.
    B. Gonadotropins
    C. Prostaglandin
    D. Prolactin

    9. Answer: A. Somatomedin-C.

    • A: Somatomedin C also called, insulin-like growth factor 1 (IGF-1),  is a protein that plays an important role in childhood growth and continues to have anabolic effects in adults.
    • B: Gonadotropins are hormones that bind to membrane-bound receptors on the cells of the gonads.
    • C: Prostaglandins play an important role in regulating smooth muscle contraction and inflammation.
    • D: Prolactin helps promote the development of the breast during pregnancy and stimulates the production of milk in the breast following pregnancy.

    10. A client arrived at the emergency department with a possible diagnosis of hyperparathyroidism. The nurse anticipates which serum electrolytes finding would be abnormal? Select all that apply

    A. Sodium
    B. Calcium
    C. Chloride
    D. Potassium
    E. Phosphorus

    10. Answer: B. Calcium, E. Phosphorus

    • B & E: A client with a parathormone deficiency has abnormal calcium and phosphorus values because parathormone regulates these two electrolytes.
    • A, C, & D: Potassium, chloride, sodium have no effect on a parathyroid hormone deficiency

    See Also


    Other anatomy and physiology study guides:

    Further Reading


    1. Nursing Diagnosis Handbook: An Evidence-Based Guide to Planning Care
    2. Medical-Surgical Nursing: Assessment and Management of Clinical Problems
    3. Medical-Surgical Nursing: Patient-Centered Collaborative Care
    4. Saunders Comprehensive Review for the NCLEX-RN Examination
    5. Brunner & Suddarth’s Textbook of Medical-Surgical Nursing

    Endocrine system | The Pig Site

    Endocrines or hormones are the substances produced by various glands, which are carried by blood or other body fluids to influence and control the pigs metabolism. There are nine main glands (Fig.1-4) in the pig which are responsible for controlling a variety of vital functions.

    Generally the diseases associated with the failure of the endocrine glands are not important in the pig. However when the regulatory and stimulatory mechanisms between the hypothalamus, the anterior pituitary gland and the ovaries fail, anoestrus (not coming on heat) or reproductive malfunction result, including cystic ovaries. In the male testicular function is affected. The hypothalamus stimulates the anterior part of the pituitary gland to release the follicle stimulating and luteinising hormones (FSH and LH). These in turn act upon the ovaries and the testes to regulate their function. (See chapter 5).

    Terminology
    Follicle stimulating hormone (FSH) – Produced by the anterior pituitary gland. It stimulates the formation of follicles in the ovaries,

    Growth hormone – Responsible for promoting growth of most tissues throughout the body. It is produced by the pituitary gland in association with the hypothalamus.

    Hypothalamus – An area in the brain responsible for providing both nervous and hormonal control over most other hormone producing glands.

    Luteinising hormone (LH) – Stimulates ovulation and is produced by the pituitary gland.

    Oestrogen – The female hormone responsible for all the female sexual characteristics. It is produced by the ovary.

    Oxytocin – Produced by the pituitary gland. This stimulates uterine contractions during farrowing and causes milk let down. It also aids in the movement of sperms and eggs.

    Progesterone – The hormone that maintains pregnancy. It is produced by the corpus luteum in the ovary.

    Prolactin – This is produced by the pituitary gland and controls milk production.

    Prostaglandins – These are produced by the uterus and the placenta and are associated with the initiation of farrowing or abortion.

    Testosterone – The male hormone responsible for all the male sexual characteristics. It also controls the development of sperm.

    90,000 To cure diabetes in Samara and Togliatti – the latest and non-traditional methods of treatment

    The endocrine system plays a special role among the regulatory systems of the human body. The endocrine system performs its functions through the hormones it produces, which enter all organs and tissues of the body, penetrating through the intercellular substance directly into the cells, or are carried through the biological system with the blood. Some of the endocrine cells are collected together and form the endocrine glands – the glandular apparatus.But in addition to this, almost any tissue of the body contains endocrine cells. A group of endocrine cells scattered throughout the body form a diffuse part of the endocrine system.

    Functions of the endocrine system and its importance for the body:

    • coordinates the work of all organs and systems of the body;
    • participates in chemical reactions in the body;
    • is responsible for the stability of all vital processes of the body under conditions of changes in the external environment;
    • , together with the immune and nervous systems, regulates human growth, development of the body;
    • participates in the regulation of the functioning of the human reproductive system and its sexual differentiation;
    • is one of the energy generators in the body;
    • participates in the formation of human emotional reactions and in his mental behavior.

    The structure of the endocrine system and diseases associated with a violation in the functioning of its constituent elements.

    I. Endocrine glands

    Endocrine glands (endocrine glands), which together make up the glandular part of the endocrine system, produce hormones – specific regulatory chemicals.

    The endocrine glands include:

    Thyroid gland. Is the largest endocrine gland. Produces hormones – thyroxine (T4), triiodothyronine (T3), calcitonin. Thyroid hormones are involved in the regulation of the processes of growth, development, differentiation of tissues, increase the intensity of metabolism, the level of oxygen consumption by organs and tissues.

    Diseases of the endocrine system associated with a violation of the functioning of the thyroid gland: hypothyroidism, myxedema (extreme form of hypothyroidism) thyrotoxicosis, cretinism (dementia), Hashimoto’s goiter, Basedow’s disease (diffuse toxic goiter), thyroid cancer.

    Parathyroid glands. Produces parathyroid hormone, which is responsible for the concentration of calcium, which is essential for the normal functioning of the nervous and motor systems.

    Diseases of the endocrine system associated with a violation of the parathyroid glands – hyperparathyroidism, hypercalcemia, parathyroid osteodystrophy (Recklinghausen’s disease).

    Thymus (thymus). It produces T cells of the immune system, secretes thymopoietins – hormones responsible for the maturation and functional activity of mature cells of the immune system.In fact, we can say that the thymus is involved in such a vital process as the production and regulation of immunity.

    In this regard, it can be argued with a high degree of probability that diseases of the endocrine system associated with disorders in the functioning of the thymus gland are diseases of the immune system. And the importance of immunity for the human body can hardly be overestimated.

    Pancreas. Is an organ of the digestive system.It produces two antagonist hormones – insulin and glucagon. Insulin lowers the concentration of glucose in the blood, glucagon increases it.

    Both hormones are involved in the regulation of carbohydrate and fat metabolism. And for this reason, diabetes and all its consequences, as well as problems associated with excess weight, are among the diseases associated with disorders in the functioning of the pancreas.

    Adrenal glands. Serves as the main source of adrenaline and norepinephrine.

    Dysfunction of the adrenal glands leads to the widest range of diseases, including serious diseases that, at first glance, are not related to diseases of the endocrine system – vascular diseases, heart disease, hypertension, myocardial infarction.

    Ovaries. Are a structural element of the female reproductive system. The endocrine functions of the ovaries include the production of the main female sex hormone antagonists – estrogens and progesterone, thus being responsible for the functioning of a woman’s reproductive function.Diseases of the endocrine system associated with functional disorders of the ovaries – fibroids, mastopathy, ovarian cysts, endometriosis, infertility, ovarian cancer.

    Testicles. Are the structural elements of the male reproductive system. male germ cells (sperm) and steroid hormones, mainly testosterone. Ovarian dysfunction leads to various disorders in the male body, including male infertility.

    2. The endocrine system in its diffuse part is represented by the following glands:

    • The pituitary gland – an extremely important gland of the diffuse endocrine system, is actually its central organ.The pituitary gland of the dough interacts with the hypothalamus, forming the pituitary-hypothalamic system. The pituitary gland produces hormones that stimulate and control virtually all other glands in the endocrine system. The anterior pituitary gland produces 6 important hormones called dominant – thyrotropin, adrenocorticotropic hormone (ACTH), 4 gonadotropic hormones that regulate the functions of the gonads and another very important hormone – somatotropin, also called growth hormone.This hormone is the main factor affecting the growth of the skeletal system, cartilage and muscles. Excessive production of growth hormone in an adult leads to agrokemalia, which manifests itself in an increase in the bones, limbs and face. The posterior lobe of the pituitary gland regulates the interaction of hormones produced by the pineal gland.
    • Epiphysis. Is a source of antidiuretic hormone (ADH), which regulates the body’s water balance, and oxytocin, which is responsible for the contraction of smooth muscles, including the uterus, during childbirth.It also secretes substances of a hormonal nature – melatonin and norepinephrine. Melatonin is a hormone that controls the sequence of sleep phases, and norepinephrine affects the circulatory system and the nervous system. Based on the foregoing, it follows that the significance of the functional status of the endocrine system is difficult to overestimate. The spectrum of diseases of the endocrine system (caused by functional disorders of the endocrine system) is very wide. In our opinion, only with an integrated approach to the body, used at the Center for Energy Information Medicine, is it possible to identify with a high degree of accuracy all the disorders in the human body, and, taking into account the individual characteristics of the patient, to develop effective measures for their correction.

    Our Center has developed a special program for the diagnosis and treatment of diseases of the endocrine system.

    Diagnostic program “Harmony of hormones” allows:

    – Identify the main causes of problems in the endocrine system. We do not determine the amount of hormones in the blood, but this is not as important for the body as the activity of hormones in the tissues, since the normal amount of the hormone in the blood may not be delivered to the cells, or not be perceived by receptors, etc.e. Our equipment makes it possible to see how the hormone works on site.

    – Get an individual program (treatment plan with specific recommendations) for outpatient treatment of the endocrine system. The treatment will be carried out by the body itself. The equipment and the doctor will help to correctly configure all systems interested in this process.

    Doctor of TSEIM Skoroumova M.G.

    Treatment of endocrine system diseases:

    The main methods for eliminating diseases of the endocrine system:

    Computer diagnostics of the body and treatment in Samara

    Modern methods of computer diagnostics make it possible not only to assess the state of health, but also to find specific causes of ailments.Professional computer diagnostics of the body in Samara will not cost you much, but it will become the starting point for effective and correct treatment.
    Computer diagnostics is based on the effect of bioresonance. Evaluation

    90,000 How do endocrine system disorders affect the digestive tract?

    We are used to associating such symptoms as nausea, vomiting, stool disorders (diarrhea or constipation) with diseases of the gastrointestinal tract, and when they appear, we turn to a gastroenterologist first.However, in some cases, in addition to the main indicators, the gastroenterologist recommends checking the work of the endocrine system or consulting an endocrinologist. Often this causes bewilderment, and sometimes even suspicion that the doctor is interested in prescribing more examinations.

    In fact, more than 80% of endocrine system diseases can be hidden behind gastroenterological symptoms, making it difficult to determine the true causes of poor health. To understand why this happens, knowledge about the structure and functions of the endocrine system will help us.

    How does the endocrine system work?

    The endocrine system consists of a network of glands, tissues and cells located throughout the body that secrete biologically active substances (hormones), and target cells that have receptors that capture these hormones. It provides regulation of such body functions as behavior, nutrition, metabolism, immunity, reproduction. That is, the endocrine system performs the coordinating function of most processes in the body.

    If the endocrine system is not healthy, a person may have developmental problems during pregnancy, growth and puberty.Endocrine disruptions can affect the functioning of various body systems, including the gastrointestinal (GI) tract.

    Hormones and their role in the body

    Hormones are chemicals that the endocrine system uses to transmit “messages” to organs and tissues throughout the body. Once in the bloodstream or in the intercellular space, they are directed to certain organs or tissues that have receptor cells that recognize the hormone and respond to it.

    Diseases of the thyroid gland and gastrointestinal tract

    Thyroid hormones, produced by the thyroid gland, help control most bodily functions, including metabolic rate and energy levels. They affect both increased appetite, the rate of secretion of digestive juices, and the motility of the gastrointestinal tract. Therefore, any deviation in the level of thyroid hormones from the norm can cause disruption of the digestive system.

    Lack of thyroid hormones (hypothyroidism) leads to a slowdown in gastric emptying and the passage of food through the intestines.The amplitude of the contractions of the large intestine also decreases. As a result, in some patients with hypothyroidism, stool frequency decreases less than once every 2 days, and in some patients there is constipation that cannot be treated with laxatives.

    Other symptoms of hypothyroidism include:

    • constant weakness, drowsiness;
    • weight gain, swelling;
    • constant chilliness;
    • slowing heart rate.

    The most common cause of hypothyroidism is autoimmune thyroiditis, associated with the aggression of the immune system against its own thyroid cells.

    An excess of thyroid hormones (thyrotoxicosis), on the contrary, causes activation of gastrointestinal motility, and as a result, patients are often disturbed by diarrhea.

    The most common symptoms of thyrotoxicosis are :

    • sharp loss of body weight;
    • increased heart rate, heart rhythm disturbance
    • increase in blood pressure
    • nervousness, irritability
    • increased sweating.

    The development of thyrotoxicosis is most often also caused by an autoimmune disease of the thyroid gland – diffuse-toxic goiter (Graves’ disease). In this case, the immune cells overstimulate the production of thyroid hormones.

    Therefore, in the presence of gastrointestinal disorders (diarrhea or constipation) of unexplained origin, it is necessary to exclude disruption of the thyroid gland.

    How are autoimmune diseases of the thyroid gland and the gastrointestinal tract related?

    Autoimmune diseases of the thyroid gland, such as autoimmune thyroiditis and diffuse-toxic goiter (Graves’ disease), are often combined with other autoimmune diseases, including liver diseases (primary biliary cirrhosis and autoimmune gastric hepatitis), autoimmune diseases (ulcerative colitis, Crohn’s disease).

    Parathyroid glands, blood and gastrointestinal calcium levels

    If many people know about the thyroid gland and its functions, then we are much less aware of the parathyroid glands. Few people know that behind the thyroid gland, on both sides, there are small paired parathyroid glands that produce parathyroid hormone, which is involved in maintaining normal blood calcium levels. If the amount of parathyroid hormone produced by the parathyroid glands increases, for example, in benign tumors of these glands, then the level of calcium in the blood also increases, and in the bone tissue, on the contrary, decreases.This condition is called primary hyperparathyroidism. An increased level of calcium from the gastrointestinal tract is manifested by a decrease or complete lack of appetite, nausea, vomiting. In addition, patients often have constipation, cholelithiasis, chronic pancreatitis, gastric ulcer and duodenal ulcer may develop.

    Other manifestations of hyperparathyroidism include increased blood pressure, fragility of bones (osteoporosis and fractures), and the formation of kidney stones (urolithiasis).

    Influence of diabetes mellitus on the digestive tract

    Diabetes mellitus is one of the most common endocrine-metabolic diseases. With a long-term course of diabetes, more than 75% of patients are concerned about various symptoms from the gastrointestinal tract:

    • constipation,
    • nausea and vomiting,
    • abdominal pain,
    • diarrhea,
    • fecal incontinence,
    • Swallowing disorder (dysphagia).

    The cause of complaints is an elevated blood sugar level and, as a consequence, the development of autonomic neuropathy – a violation of the sensitivity of nerve fibers due to damage to small blood vessels. In addition, diabetes mellitus increases the susceptibility to infections that can cause the development of diseases of the gastrointestinal tract.

    Gastroenterological manifestations of tumors of the diffuse endocrine system (carcinoids)

    The diffuse endocrine system is the most mysterious and currently the most studied part of the endocrine system.It includes single, or grouped together, hormonally active cells located throughout the body in the endocrine and non-endocrine organs.

    Since the end of the 19th century, when the first cells of the diffuse endocrine system were described, more than 60 of their species have been studied. A significant number of these cells are found in the digestive tract, heart, thymus, in the mucous membranes of various organs and tissues. Cells produce hormones and biologically active substances that are involved in the regulation of vital processes in the body.

    Benign and malignant neoplasms from cells of the diffuse endocrine system are called neuroendocrine tumors (carcinoids), most often such tumors arise in the gastrointestinal tract, but they can also affect other organs. A feature of these neoplasms is that, in an active state, they are capable of producing a large amount of hormones, causing syndromes associated with an excess of these hormones.

    The gastrointestinal tract is the largest producer of hormones, at the moment there are more than 10 different biologically active substances involved, primarily in the processes of digestion and metabolism.Tumors originating in the gastrointestinal tract can cause carcinoid syndrome, which is manifested by diarrhea, cramping abdominal pain, flushing of the face and trunk, increased heart rate, and shortness of breath.

    Summing up

    Most of the endocrine disorders described in this article were encountered in the clinical practice of gastroenterologists and endocrinologists of our center. Carcinoid syndrome, which occurs in neuroendocrine tumors of the gastrointestinal tract, is the rarest endocrine disorder.But endocrine disorders leading to gastroenterological manifestations caused by diseases of the thyroid and parathyroid glands are widespread in the North-West region .

    You can check the state of these glands using the “express diagnostics” programs:

    Programs were developed by our doctors based on their diagnostic and treatment experience, as well as in accordance with Russian and international clinical guidelines.You can sign up for a survey or clarify your questions by calling +7 (812) 426-33-88 or through the form on the website.

    Endocrine diseases – diagnosis and treatment in Moscow, price

    Endocrine diseases relate to the work of the endocrine glands, and in recent years their frequency has increased. This also applies to diseases of the thyroid gland, and diabetes mellitus, and other serious disorders.

    Experts note that the manifestations of endocrine problems are diverse, therefore, they are often found not by endocrinologists, but by doctors of other specialties.In particular, many patients come with anxiety to a therapist who can refer the patient to the necessary examination.

    Therapists of the Yauza Clinical Hospital work in close cooperation with experienced endocrinologists, who in each case prescribe an individual treatment regimen. The therapist continues to observe the patient throughout the treatment, monitoring its effectiveness.

    The main causes of endocrinological diseases

    Often, doctors find it difficult to quickly name the cause of the development of an endocrine disease, i.e.because there are many factors that cause pathology. Moreover, in some cases, the cause of the disease remains unknown there.

    The main factors that lead to the development of endocrine disorders include the following:

    • tumors of glandular tissues
    • cysts
    • infectious diseases
    • hereditary factor
    • chronic diseases of other organs and systems
    • cardiovascular failure
    • surgical interventions
    • taking a number of drugs

    Since the hormones produced by the endocrine glands regulate the work of other organs and systems, endocrine diseases disrupt metabolism and symptoms that are characteristic, for example, of diseases of the skin, kidneys, etc.In general, this makes diagnosis difficult.

    Most common endocrine disorders

    Diabetes mellitus – a chronic disease associated with metabolic disorders, in which the body produces insufficient insulin or decreases its effectiveness with an increased level of glucose.

    Diabetes insipidus (diabetes insipidus) – a disease associated with the inability of the kidneys to concentrate urine and reabsorb water, which is caused by the absence or decrease in the secretion of the antidiuretic hormone vasopressin, or immunity to it of the epithelium of the renal tubules.

    Obesity is a disease characterized by excessive deposition of adipose tissue in the body. The main symptoms of primary obesity: fatigue, apathy, weakness, drowsiness, shortness of breath, increased appetite, dry skin or, conversely, sweating, fungal diseases, skin inflammation, hypersecretion of gastric juice.
    The symptoms of secondary obesity are determined by the underlying disease.

    Osteoporosis is a progressive systemic disease in which the structure of bone tissue is disturbed, its density decreases due to partial resorption of bone substance.Bones become fragile and prone to fracture, even under light loads.

    Thyrotoxicosis (hyperthyroidism) – a condition caused by an excessive content of thyroid hormones in the body, which leads to metabolic disorders, functions of the nervous and cardiovascular systems.

    Thyroiditis – inflammation of the thyroid gland, which is manifested by pain when swallowing and moving the head back, an increase in the size of the neck, soreness of the lymph nodes, fever, throbbing pain in the ears, tachycardia, chills.

    Diagnostics and treatment of endocrine diseases in the Clinical Hospital on Yauza

    Doctors of the therapy department of the Clinical Hospital on Yauza have all the facilities for high-quality diagnostics of endocrine diseases. As a rule, for a comprehensive diagnosis, it is necessary to conduct laboratory tests of urine and blood, to do special hormonal studies, as well as ultrasound, and, if necessary, CT, MRI and ECG. All these opportunities are available at the Clinical Hospital on Yauza.

    After examination and establishment of a preliminary diagnosis, the therapist usually refers the patient to an endocrinologist for consultation, who specifies the diagnosis and prescribes the optimal treatment. In this case, the patient remains under the supervision of the therapist until the end of the treatment.

    Cost of services

    Prices for services You can look at the price list or specify by phone, indicated on the website.

    Human endocrine system – BU “Second City Hospital” of the Ministry of Health of Chuvashia

    Human endocrine system

    The endocrine system is understood as a set of endocrine glands that produce special substances – hormones, characterized by high biological activity (ensuring the body’s vital processes: growth, development, reproduction, adaptation, behavior).

    The most important for the human body are the pituitary gland, hypothalamus, thyroid and parathyroid glands, adrenal glands, sex glands and pancreas. There are also many other glands, but their structure and action are not fully understood.

    The central link of the endocrine system is the hypothalamus and pituitary gland. The hypothalamus, in response to nerve impulses, has a stimulating or inhibitory effect on the anterior pituitary gland.Through the pituitary hormones, the hypothalamus regulates the function of the peripheral endocrine glands.

    Peripheral link of the endocrine system – adrenal glands, thyroid gland, parathyroid glands, testes, ovaries, islets of Langerhans (pancreas).

    The main functions of the endocrine glands.

    The hypothalamus is one of the brain regions.The main function of the hypothalamus, located at the base of the human skull, is to stimulate and control the work of all other organs of the endocrine and other body systems. It synthesizes hormones – vasopressin (takes part in the regulation of blood pressure, urination) and oxytocin (regulation of the activity of the muscles of the uterus), pituitary hormones (liberins and statins).

    Pituitary gland is considered one of the main endocrine glands in the human body.It is located in a special depression of the sphenoid bone of the cerebral skull. The main hormones of the pituitary gland: somatotropic (growth hormone), thyroid-stimulating, follicle-stimulating, luteinizing, adrenocorticotropic, lactogenic (prolactin). Growth and reproduction depend on the normal functioning of the pituitary gland; basic, carbohydrate, mineral, fat and protein metabolism.

    The thyroid gland is located on the anterior surface of the neck. The hormones produced by the thyroid gland (thyroxine and triiodothyronine) provide growth, mental and physical development, and regulate the rate of metabolic processes.

    Parathyroid gland produces parathyroid hormone (parathyroid hormone), which is involved in the regulation of calcium and phosphorus metabolism in the body.

    Disruption of the pancreas and provokes the occurrence of such a common disease as diabetes mellitus. It produces glucagon and insulin, which are responsible for the metabolism and absorption of carbohydrates.

    The adrenal glands are two small glands located in the adrenal region.The basis of the adrenal gland is the medulla, which produces such important hormones as adrenaline and norepinephrine. They affect the state of the blood vessels, and norepinephrine narrows the vessels of all sections, with the exception of the brain, and adrenaline narrows part of the vessels, and partly expands. Adrenaline intensifies and speeds up heartbeats, while norepinephrine, on the contrary, can lower them. The adrenal cortex produces three types of corticosteroid hormones (aldosterone, cortisol, androgens) that affect the metabolism of carbohydrates, electrolytes and gonads.

    Sex glands are responsible for human reproduction. In the male gonads (testicles), the male sex hormone testosterone is produced, and in the female (ovaries) – estrogen and progesterone, which control all the changes that occur in the uterus during the menstrual cycle and pregnancy.

    The loss of each of the components of hormonal regulation from the general system disrupts a single chain of regulation of body functions and leads to the development of various pathological conditions.

    Pathology of the endocrine system is expressed by diseases and pathological conditions, which are based on hyperfunction, hypofunction or dysfunction of the endocrine glands.

    Among the most common endocrine diseases and pathological conditions, it should be noted diabetes mellitus and insipidus, diffuse toxic goiter (thyrotoxicosis), hypothyroidism, adrenal insufficiency, dysfunctions of the gonads and others.

    Endocrine function of the pancreas in experimental diabetes mellitus in rats and its features in adaptation to hypoxia | Kolesnik

    It is well known that diabetes mellitus is a polyhormonal disease. Although insulin plays a leading role in its pathogenesis, other hormones also play an important role in its development and course. This primarily refers to glucagon and somatostatin [8]. These hormones are synthesized in the A and D cells of the islets of Langerhans and, together with insulin-producing B cells, form a single endocrine complex involved in the regulation of carbohydrate homeostasis [10, 11].The methods currently used by most researchers to assess the state of the endocrine function of the pancreas are based on radioimmunological methods for the determination of insulin, C-peptide, glucagon and somatostatin in the blood. However, the concentration of the hormone in the blood depends on many factors, such as the secretory activity of endocrine cells, the phase of secretion (accumulation or excretion), the process of inactivation, interaction with receptors, the possibility of hormone production by other endocrine cells.Therefore, it is possible to adequately assess the state of the secretory function of endocrine cells only in a comprehensive manner, by determining the concentration of the corresponding hormone in the blood (by radioimmunological method) and its content in A-, B- and D-cells (by immunocytochemical method). Taking into account the above, the aim of this study was a comprehensive study of the state of the endocrine apparatus of the pancreas in experimental diabetes mellitus, adaptation to hypoxia and their combination, which would reveal the peculiarities of the relationship between A-, B- and D-cells in different conditions.Materials and Methods The study was carried out on 80 Wistar rats of both sexes weighing 200-230 g, which were on a standard diet under the same conditions. All animals were divided into 4 experimental groups: 1st – intact animals; 2nd – animals with diabetes mellitus; 3rd – animals that have undergone adaptation to hypoxia for 21 days; 4th – animals with diabetes mellitus, which from the 16th day of modeling of the disease were subjected to adaptation to hypoxia. Each experimental group consisted of 10 animals.Radioimmunological and immunocytochemical studies were carried out on the same animals. Diabetes mellitus (mild course) [1] was modeled by intraperitoneal injection of 50 mg / kg streptozotocin [12]. Adaptation to hypoxia was carried out by daily placing the animals in a ventilated pressure chamber for 6 hours, in which the air rarefaction corresponded to 1 km on the 1st day, 2 km on the 2nd day, and on the 3rd day – Table I Concentration of glucose and pancreatic hormones. glands in the peripheral blood of rats (Af ± m) Series of experiments Glucose, mmol / L Insulin, μU / ml Glucagon, pg / ml Somatostatin, pg / ml Control 4.62 ± 0.24 34.7 ± 3.6 67.8 ± 3.8 18.5 ± 1.5 4.90 ± 0.11 31.5 ± 4.9 75.8 ± 14.3 – Diabetes (16 days) 6.36 ± 0.34 ** 15.4 ± 4.2 ‘* 66.8 ± 9.9 19.5 ± 1.9 6.09 ± 0.52 ** 13.8 ± 3.7 ** 122.4 ± 21.3 – Diabetes (37 days ) 8.78 ± 0.59 ** 11.4 ± 3.8 ‘* 90.6 ± 7.6 * 24.4 ± 2.1 ** 7.59 ± 0.88 ** 12.3 ± 1 , 1 “150.2 ± 22.3 ** – Adaptation to hypoxia (21 days) 3.52 ± 0.29 ** 32.6 ± 6.2 105.6 ± 10.4 ** 38.3 ± 5 , 2 ** 4.00 ± 0.17 ** 30.4 ± 4.7 93.8 ± 8.9 – Diabetes followed by adaptation to hypoxia 7.59 ± 0.46 ** 30.4 ± 4.1 88.4 ± 7.2 * 41.3 ± 8.4 ** 6.06 ± 0.56 26.4 ± 2.3 131.6 ± 24.9 Note.The blood concentration of somatostatin in females was not determined. One asterisk – p <0.05, two - p <0.01. Here and in table. 2 in the numerator - the content in males, in the denominator - in females. 3 km, on the 4th day - 4 km, on the 5th day - 5 km, on the 6th day and further until 21 days - 6 km [4]. In group 4, animals, starting from the 16th day of modeling the disease, were subjected to adaptation to hypoxia according to the above scheme for 21 days. The animals were sacrificed for taking blood and pancreas according to generally accepted rules at the same time of day after a 16-hour fast; in the 2nd group - on the 16th and 37th days, in the 3rd - on the 22nd day, in the 4th - on the 37th day.The concentration of hormones in the blood was determined by radioimmunoassay using standard kits for the determination of insulin (RIO-INS-1-M, USSR), glucagon (BIODATA, Italy), somatostatin (INSTAR, USA). Quantitative immunocytochemical determination of insulin in B-cells, glucagon - in A-cells, somatostatin - in D-cells was carried out by the method of indirect immunofluorescence using kits manufactured by Amer- sham (England). Monoclonal antibodies to insulin and rabbit antisera to glucagon and somatostatin were used as primary antibodies; rabbit antibodies to mouse IgG and rat to rabbit IgG conjugated to FITC were secondary antibodies.The detection of hormones in the cells was carried out on serial sections with a thickness of 4 μm, taken from different parts of the pancreas. Sections enclosed in a mixture of phosphate buffer and glycerol (9: 1) were studied under a LUMAM-I2 fluorescent microscope with an FMEL-1A photometric attachment. We used a 40X objective, 0.5 probe, 480 nm wavelength, typical for FITC. The content of hormones in cells, which is directly proportional to the intensity of fluorescence, was expressed in conditional microunits obtained by processing a signal in millivolts from a V7-16A digital voltmeter coupled to the Electronica DZ-28 computer.In each group, 200-400 cells were examined. In addition, in all animals in all experimental groups, serum glucose was determined by the orthotoluidine method and a glucose tolerance test was performed (4 g / kg intraperitoneally). The research results were subjected to statistical processing on an ATARI 130XE PC. RESULTS AND DISCUSSION When streptozotocin was administered, the blood glucose level in rats gradually increased (Table 1), and the tolerance test also changed (the glycemic level 2 h after glucose administration was higher than the initial one, while in intact animals it decreased).In animals with diabetes mellitus on the 16th day and even more so on the 37th day, the insulin concentration in the blood serum was significantly reduced (see Table 1). In the pancreas, immunocytochemical studies revealed a decrease in fluorescence intensity, which is associated with a decrease in insulin content in B cells (Table 2). In addition, destruction of a part of the islets was found, which was especially pronounced on the 37th day, and the large islets were mostly affected, while the small ones remained practically intact.A more pronounced decrease in the insulin content in B cells was observed in males (see Table 2). It should be noted that a small number of single B cells appeared among the acinar tissue of the pancreas, which was not observed in intact animals. Plasma glucagon concentration significantly increased, especially towards the end of the study. In A-cells on the 16th day, the glucagon content in females was also increased, as in plasma, while in males it was significantly reduced, which, apparently, is associated either with the process of intensive excretion of the hormone into the blood. or with a depressing effect on its secretion of somatostatin.On the 37th day, the glucagon content significantly increased in both males and females, but to a greater extent in males, while the A-cells were hypertrophied. The concentration of somatostatin in the blood plasma also gradually increased, reaching significant differences compared to the control only. 14.7 *** 979.5 ± 16.8 *** Diabetes 618.7 ± 16.8 *** 1485.1 ± 13.3 *** 1075.0 ± 20.6 *** (37 days) 758.5 ​​± 12.9 *** 1398.4 ± 11 ...6 *** 1135.0 ± 19.3 *** Adaptation to hy- 1648.3 ± 27.6 ** 1141.2 ± 12.3 ** 722.9 ± 12.7 ** poxia (21 days) 1670.1 ± 17.7 * ** 1089.9 ± 14.7 *** 691.9 ± 18.8 Diabetes with after- 1298.4 ± 11.2 *** 1326.4 ± 15.2 * 792.2 ± 17.4 following adaptation to hy- 1259 , 8 ± 9.8 '** 1301.2 ± 14.9 *** 767.1 ± 15.4 ** Poxia Note. One asterisk - p <0.005, two - p <0.01. three - p <<0.001. ko on the 37th day. In contrast to plasma, the content of somatostatin in D cells increased significantly already on the 16th day and did not change in males, but continued to increase in females.Thus, the increase in the content of somatostatin in D cells was not accompanied by its adequate increase in the peripheral blood. It should also be noted that D-cells increased in size under these conditions and more and more resembled in structure neurons with processes containing the hormone. In 111 series of experiments, adaptation of animals to hypoxia for 21 days led to the development of moderate hypoglycemia. The insulin concentration in the blood serum was at the control level. The insulin content in B cells was significantly higher than in intact animals.In addition, a large number of single cells reacting with monoclonal antibodies to insulin were found in pancreatic sections. These data indicate that under conditions of hypoxic training, the synthetic activity of B cells increases, as well as new insulinocytes appear, possibly originating either from the epithelium of the excretory ducts [2, 6], or from the so-called acinisle. The content of glucagon in blood plasma was increased, while in A-cells it was significantly reduced, which is apparently associated with increased excretion of the hormone in response to developing hypoglycemia [5].The concentration of somatostatin in plasma under these conditions was significantly increased, while its content in D cells in males was significantly reduced, and in females it remained at the control level. Hypoxic training in animals with diabetes mellitus led to a slight decrease in the level of glycemia and a normalization of the glucose tolerance test. The serum insulin concentration almost reached the control level. In the pancreas, a decrease in the number of islets with signs of destruction was noted, and the insulin content in B cells increased significantly in comparison with animals of the 2nd group (on day 37), which were not subjected to hypoxic training, accounting for about 80% of the control level.The concentration of glucagon in the blood and its content in A-cells decreased in comparison with those in animals with diabetes, but still remained higher than in intact animals. The content of somatostatin in D cells also decreased significantly, but its concentration in the blood remained at a fairly high level. Thus, the studies carried out have shown that an adequate assessment of the state of the endocrine function of the pancreas is possible only when using a set of methods - immunocytochemical and radioimmunological.In addition, from the above data, it follows that the development of the initial stages of diabetes mellitus is accompanied by the restructuring of the entire endocrine pancreas. In response to a sharp decrease in insulin content, glucagon secretion is compensatory activated in order to adequately supply tissues with glucose, as well as to stimulate the remaining intact B cells (9, 10]. The role of somatostatin is not so unambiguous, since this hormone, having a wide spectrum of action [7] can give different, sometimes even the opposite effect.Thus, it is known that somatostatin, produced in D cells of the pancreas, can inhibit the activity of A and B cells, and somatostatin, produced in the hypothalamus, can inhibit the production of somatotropic hormone, which is a diabetogenic factor [3]. In our studies, the results of which are supposed to be considered in a separate article, signs of hypertrophy of somatostatin-producing hypothalamic neurons located in the arcuate and periventricular nuclei were found, as well as significant changes in the concentration of immunoreactive somatostatin in the outer zone of the median eminence of the hypothalamus.The results of these studies have shown a positive effect of adaptation to hypoxia on the state of the pancreas in animals with diabetes. The mechanism of this influence is rather complex and diverse, but based on the data obtained, several of its links can be represented. This is primarily the stimulation of insulin biosynthesis in B cells, inhibition of the process of their destruction, and the appearance of new insulinocytes. An important role is also played by a decrease in the activity of A and D cells, which leads to a decrease in the level of glycemia and an increase in the activity of B cells.It is known that an adequate response of A cells depends on the state of B cells (9]. Apparently, stimulation of insulin biosynthesis under conditions of adaptation to hypoxia leads to the normalization of the response of A cells to hyperglycemia, which is impaired in diabetes [9]. , it was shown that the course of diabetes mellitus and changes in the pancreas have features depending on the sex of the animals. Conclusions 1. A comprehensive study of the endocrine function of the pancreas showed that the development of diabetes mellitus is associated with the restructuring of all components of the islets of Langerhans and has its own characteristics depending on gender of animals.2. Adaptation to hypoxia has a positive effect on the development of experimental diabetes mellitus in rats.

    1. Experimental diabetes mellitus: Role in clinical diabetology / Baranov V. G., Sokoloverova I. M. Gasparyan E. G. et al. – L., 1983.

    2. Zarechnova NN // Questions of morphology.- Frunze, 1987. – S. 62-64.

    3. Kendysh I. N. Regulation of carbohydrate metabolism. – M., 1985.

    4. Yu. M. Kolesnik and AV Abramov, Physiol. jury.- 1992.- T. 38. No. 3.- S. 60-63.

    5. Palyuk P. Mf. // Ibid. – 1990. – T. 36, No. 1.- S. 113-121.

    6. Tomilina T. A., Abdurakhmanov M., Malikov 3. V. // Compensatory and adaptive processes in the cells of the internal environment.- Tashkent, 1988.- P. 67-71.

    7. Shusdziarra V. // Physiology and pathophysiology of the gastrointestinal tract: Per. from English – M., 1989. – S. 87-106.

    8.Bolaffi J. L., Rodd G., Ma Yanhui, Grodsky G. M. // Endocrinology. 1990, Vol. 126, No. 3.- P. 1750-1755.

    9. McCulloch D. K., Raghu P. K., Koerker D. J. et al. // Metabolism, 1989. – Vol. 38, No. 7.- P. 702-707.

    10. Pipeleers D. G., Schit F. C., In’t Veld P. A. et al. // Endocrinology. 1985, Vol. 117, No. 3.- P.824-833.

    11. Schravedijk C. F. H., Foriers A., Hoodhe-Peters E. L. et al. // Ibid. – P. 841-848.

    12. Steger R. W., Kienast S. G. // Diabetes. 1990. Vol. 39, No. 8.- P. 942-948.

    Nervous and endocrine systems

    The exposition of the hall is devoted to the structure and functions of the nervous and endocrine systems of animals and humans.It opens with the section “Evolution of the nervous system”, which shows the development of the nervous system in invertebrates and vertebrates. The material on the development of brain regions in vertebrates is presented in detail. In the section “The structure of the nervous system” you can see models of various types of nerve cells, natural preparations of the human spinal cord and brain. The hall shows the connection of the sense organs with the central nervous system, shows examples of conditioned and unconditioned reflexes in animals.

    Separately, the exposition pays attention to the physiology of higher nervous activity, that is, the function of the higher part of the central nervous system – the cerebral cortex, through which the most complex relations of the organism with the environment are provided.Expressive biogroups “Maternal instinct of a leopard”, “Orientation reflex of a speckled ground squirrel”, “Defensive reflex of a hedgehog” and others demonstrate various manifestations of higher nervous activity in animals.

    In the section “The Brain – the Material Basis of Thinking and Consciousness” of particular interest are materials on the methodology of Professor I. A. Sokolyansky’s work with deaf-blind and dumb people, which gives people, deprived of sight and hearing, the opportunity to navigate the world. Here are the sculptural works of a deaf-blind-mute girl, which amaze with the abundance of details and the accuracy of the execution of various objects.

    The activity of the animal and human body is regulated by the nervous system in interaction with the endocrine system, which is devoted to the next section of the exposition. Shown here are wet preparations of endocrine glands in health and disease. You can also see unique exhibits reflecting experiments to study the effect of the pituitary gland, thyroid and gonads on the body of animals. Work on animals laid the foundations for the method of hormonal determination of pregnancy and the sex of the fetus. These works were carried out by a group of scientists led by the founder and first director of the museum B.M. Zavadovsky.

    The exposition of the hall was created in 1984. The author of the exposition is I. V. Polikarpova, the leading artist is V. Ya. Grachev.

    The hall conducts excursions “Who is the head of everything” for junior schoolchildren, “The nervous system and higher nervous activity” (with demonstration of experiments) and “Endocrine glands” for senior pupils and students. A practical lesson “Muscle Physiology” is held.

    90,000 Gynecological manifestations of endocrine pathology

    Gynecological manifestations of endocrine pathology

    Diseases of the endocrine system are diverse both in the localization of the lesion and in their manifestations.The organs of internal secretion produce hormones that regulate the growth, development and functioning of all organs and systems of our complex organism. Gynecological endocrinology is a large branch of medicine dealing with the problems of hormonal regulation of the female reproductive system, and the gynecologist-endocrinologist is a highly qualified specialist who deeply understands the mechanism of action of each hormone and their delicate interaction in the field of women’s health.

    What diseases can a gynecologist-endocrinologist treat?

    The specialist in gynecological endocrinology is engaged in the diagnosis and treatment of the following diseases:

    1. Infertility resulting from hormonal imbalance.
    2. Violation of the menstrual cycle.
    3. Hirsutism.
    4. Polycystic ovary syndrome.
    5. Certain types of acne.
    6. Severe premenstrual syndrome.
    7. Pathological manifestations of menopause.

    In addition, a gynecologist-endocrinologist consults women during pregnancy, prescribes supportive therapy for normal menopause, selects hormonal contraceptives, taking into account the characteristics of a woman’s hormonal status.

    Diagnosis and treatment of endocrinological diseases of the female genital area

    Reception of a specialist in gynecological endocrinology differs from the usual consultation in duration: in order to make an accurate diagnosis, the doctor must assess the function of almost every system of the woman’s body.