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Human endocrine system parts and functions: Illustrations of Anatomy, Function, Glands $ Organs


Communication between the Brain and the Body

Hormones are important messages both within the brain and between the brain and the body.

In addition to the nervous system, the endocrine system is a major communication system of the body. While the nervous system uses neurotransmitters as its chemical signals, the endocrine system uses hormones. The pancreas, kidneys, heart, adrenal glands, gonads, thyroid, parathyroid, thymus, and even fat are all sources of hormones. The endocrine system works in large part by acting on neurons in the brain, which controls the pituitary gland. The pituitary gland secretes factors into the blood that act on the endocrine glands to either increase or decrease hormone production. This is referred to as a feedback loop, and it involves communication from the brain to the pituitary to an endocrine gland and back to the brain. This system is very important for the activation and control of basic behavioral activities, such as sex; emotion; responses to stress; and eating, drinking, and the regulation of body functions, including growth, reproduction, energy use, and metabolism. The way the brain responds to hormones indicates that the brain is very malleable and capable of responding to environmental signals.

The brain contains receptors for thyroid hormones (those produced by the thyroid) and the six classes of steroid hormones, which are synthesized from cholesterol — androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and vitamin D. The receptors are found in selected populations of neurons in the brain and relevant organs in the body. Thyroid and steroid hormones bind to receptor proteins that in turn bind to DNA and regulate the action of genes. This can result in long-lasting changes in cellular structure and function.

The brain has receptors for many hormones; for example, the metabolic hormones insulin, insulin-like growth factor, ghrelin, and leptin. These hormones are taken up from the blood and act to affect neuronal activity and certain aspects of neuronal structure.

In response to stress and changes in our biological clocks, such as day and night cycles and jet lag, hormones enter the blood and travel to the brain and other organs. In the brain, hormones alter the production of gene products that participate in synaptic neurotransmission as well as affect the structure of brain cells. As a result, the circuitry of the brain and its capacity for neurotransmission are changed over a course of hours to days. In this way, the brain adjusts its performance and control of behavior in response to a changing environment.

Hormones are important agents of protection and adaptation, but stress and stress hormones, such as the glucocorticoid cortisol, can also alter brain function, including the brain’s capacity to learn. Severe and prolonged stress can impair the ability of the brain to function normally for a period of time, but the brain is also capable of remarkable recovery.

Reproduction in females is a good example of a regular, cyclic process driven by circulating hormones and involving a feedback loop: The neurons in the hypothalamus produce gonadotropin-releasing hormone (GnRH), a peptide that acts on cells in the pituitary. In both males and females, this causes two hormones — the follicle-stimulating hormone (FSH) and the luteinizing hormone (LH) — to be released into the bloodstream. In females, these hormones act on the ovary to stimulate ovulation and promote release of the ovarian hormones estradiol and progesterone. In males, these hormones are carried to receptors on cells in the testes, where they promote spermatogenesis and release the male hormone testosterone, an androgen, into the bloodstream. Testosterone, estrogen, and progesterone are often referred to as sex hormones.

In turn, the increased levels of testosterone in males and estrogen in females act on the hypothalamus and pituitary to decrease the release of FSH and LH. The increased levels of sex hormones also induce changes in cell structure and chemistry, leading to an increased capacity to engage in sexual behavior. Sex hormones also exert widespread effects on many other functions of the brain, such as attention, motor control, pain, mood, and memory.

Sexual differentiation of the brain is caused by sex hormones acting in fetal and early postnatal life, although recent evidence suggests genes on either the X or Y chromosome may also contribute to this process. Scientists have found statistically and biologically significant differences between the brains of men and women that are similar to sex differences found in experimental animals. These include differences in the size and shape of brain structures in the hypothalamus and the arrangement of neurons in the cortex and hippocampus. Sex differences go well beyond sexual behavior and reproduction and affect many brain regions and functions, ranging from mechanisms for perceiving pain and dealing with stress to strategies for solving cognitive problems. That said, however, the brains of men and women are more similar than they are different.

Anatomical differences have also been reported between the brains of heterosexual and homosexual men. Research suggests that hormones and genes act early in life to shape the brain in terms of sex-related differences in structure and function, but scientists are still putting together all the pieces of this puzzle.

How do nerves control every organ and function in the body?

Category: Biology      Published: September 20, 2013

Nerves do not control every tissue and function in the human body, although they do play a large role. There are three main ways that bodily organs and functions are controlled:

  1. Through the central nervous system
  2. Through the endocrine system
  3. Through local self-regulation (which includes intracrine, autocrine, paracrine, and immune regulation)

Nerves carry orders from the brain and spinal cord in the form of electrical signals. Nerves also help sense the state of tissues and relay this information back to the brain and spinal cord, enabling us to experience pain, pleasure, temperature, vision, hearing, and other senses. The body uses electrical signals sent along nerves to control many functions because electrical signals can travel very quickly. At the end of each nerve’s axon terminals the electrical signals are converted to chemical signals which then trigger the appropriate response in the target tissue. However, the control exerted by the nervous system inevitably resides in the brain and spinal cord, an not in the nerves, which just pass along the signals. Most signals get processed in the brain, but high-risk signals are processed and responded to by the spinal cord before reaching the brain in the effect we call “reflexes”. Although the central nervous system plays a large role in controlling the body, it is not the only system that exerts control.

The molecular structure of thyroid hormone (T3), which regulates the rate of energy use in the body. Public Domain Image, source: Wikipedia.

The endocrine system is a series of endocrine glands throughout the body that excrete certain chemical signals called hormones into the blood stream. The circulating blood then takes the hormones throughout the entire body where different tissues respond in characteristic ways to the hormones. The response of an organ or system to a hormone depends on how much of that hormone is present in the blood. In this way, endocrine glands can exert control over different organs and functions of the body by varying how much hormone they emit. In contrast to the central nervous system, the pathway of control for the endocrine system is purely chemical and not electrical. For example, the thyroid gland in the neck controls how quickly the body uses energy by secreting varying levels of thyroid hormone. Too much thyroid hormone, and you become restless, jittery, and unable to sleep. Too little thyroid hormone and you become sleepy, lethargic, and enable to think straight. A healthy body constantly monitors the activity level and adjusts the thyroid hormone levels as needed.

Other examples of endocrine glands are the adrenal glands, which prepare the body for facing an emergency, and the reproductive glands, which control body mass and reproduction. Hormones in the body control functions as diverse as libido, fertility, menstruation, ovulation, pregnancy, child birth, lactation, sleep, blood volume, blood pressure, blood sugar, the immune system, vertical growth in children, muscle mass, wound healing, mineral levels, appetite, and digestion. Ultimately, much of the endocrine system is subservient to the brain via the hypothalamus, but the endocrine system does operate somewhat independently using feedback loops.

Lastly, organs and functions in the body are controlled through local self-regulation. Rather than depend on the brain to dictate every single minute task, organs and cells can accomplish a lot on their own so that the brain is freed up for more important tasks. An organ can communicate regulatory signals through its interior using localized chemical signals such as paracrine hormone signalling. Typically, such hormones do not enter the blood stream, but are transported locally by simply flowing in the space between cells. This approach works because paracrine hormones are only meant to operate on nearby cells. For example, the clotting of blood and healing of wounds are controlled locally through an exchange of paracrine hormones. The organ with the highest degree of self-regulation is probably the liver. The liver hums along nicely, performing hundreds of functions at once without much direction from the rest of the body. An organ can also communicate through its interior electrochemically. For instance, the heart does not beat because a nerve is telling it to. The heart beats on its own through a cyclic wave of electrical impulses. While it is true that the brain can tell the heart to speed up or slow down, the actual beating of the heart is controlled locally.

Also, each cell of the body has some degree of self-regulation internal to the cell itself. Some cells exert more internal control than others. For instance, white blood cells hunt down and destroy germs in a very independent fashion, as if they were autonomous organisms. Active white blood cells do not wait for the brain or a hormone to tell them to do their job. Sperm cells are so autonomous that they can continue to survive and function properly even after completely leaving the male’s body.

In reality, the central nervous system, the endocrine system, and the local regulation systems are not independent, but exert control over each other in a complicated manner.

brain, endocrine, endocrine system, hormones, nerve, nerves, nervous system, paracrine, signalling

Human Endocrine System – Function, Glands and Hormones In Humans

The human endocrine system is a messenger system that regulates distant target organs through feedback loops of hormones released by the internal glands of an organism directly into the circulatory system. In vertebrates, the hypothalamus is the neural control node for all endocrine systems. 

The endocrine system is a system of glands and organs that is located all around the body. It functions similarly to the nervous system in that it controls and regulates all of the body’s functions.

Although the nervous system communicates through nerve impulses and neurotransmitters, the endocrine system communicates through chemical messengers known as hormones.

The thyroid gland and the adrenal glands are the two main endocrine glands in humans. The study of the endocrine system and its disorders is known as endocrinology. Endocrinology is a subspecialty of internal medicine.

Functions of Human Endocrine System

The endocrine system regulates a variety of body functions through hormone release.

Hormones are produced by the endocrine system’s glands and pass through the bloodstream to different organs and tissues in the body. Hormones then instruct these organs and tissues about how to act.

The Endocrine System is in Control of the Following Bodily Functions:

  • Metabolic rate

  • Development and growth of a human being

  • Reproduction and sexual function

  • Heart Rate

  • Blood pressure 

  • The appetite that is the need to eat

  • Controls cycles of sleep and wakefulness

  • Controls the temperature of the body

Human Endocrine Glands

The human endocrine system is made up of a complex network of glands that secrete different hormones in human body. Hormones are produced, stored, and released via the endocrine glands in human beings. Each gland produces one or more hormones that target specific organs and tissues in the body.

The List of All Important Endocrine Glands in Human Body are as Follows:

  1. Hypothalamus

  • The hypothalamus is a part of the brain that houses a number of small nuclei that perform various functions. 

  • One of the hypothalamus’ most essential functions is to connect the nervous and endocrine systems via the pituitary gland. 

  • The limbic system includes the hypothalamus, which is situated under the thalamus.

  • The hypothalamus is in charge of regulating certain metabolic processes as well as other autonomic nervous system behaviours. 

  • It produces and secretes certain neurohormones known as releasing hormones or hypothalamic hormones, which stimulate or inhibit the pituitary gland’s hormone secretion. 

  • Body temperature, appetite, essential aspects of parenting and attachment behaviours, thirst, fatigue, sleep, and circadian rhythms are all regulated by the hypothalamus.

  1. Pituitary Gland (Human Body Master Gland)

  • The pituitary gland which is the master gland of the human body, also known as the hypophysis, is a small endocrine gland that weighs about 0.5 grammes and is about the size of a pea.

  • Since it regulates the activities of many other endocrine glands, the pituitary gland is known as the master gland of the human body.

  • It’s a protrusion at the base of the brain that protrudes from the bottom of the hypothalamus.

  • The hypophysis is found in the centre of the middle cranial fossa, on the hypophyseal fossa of the sphenoid bone, and is enclosed by a narrow bony cavity (sella turcica) filled by a dural fold (diaphragma sellae).

  • The anterior pituitary, also known as the adenohypophysis, is a lobe of the pituitary gland that controls stress, development, reproduction, and lactation.

  • Melanocyte-stimulating hormone is synthesised and secreted by the intermediate lobe.

  • The neurohypophysis, or posterior pituitary, is a lobe of the pituitary gland that is functionally linked to the hypothalamus by the median eminence by a narrow tube known as the pituitary stalk, also known as the infundibulum.

  • The pituitary gland secretes hormones that regulate development, blood pressure, energy balance, all sex organ functions, thyroid gland function, and metabolism, as well as some aspects of pregnancy, childbirth, breastfeeding, water/salt concentration in the kidneys, temperature regulation, and pain relief.

  1. Pineal Gland

  • The pineal gland, also known as the epiphysis cerberin, is a small endocrine gland found in most vertebrates’ brains.

  • Melatonin, a serotonin-derived hormone produced by the pineal gland, regulates sleep patterns in both circadian and seasonal cycles.

  • The pineal gland is tucked in a groove where the two halves of the thalamus meet in the epithalamus, near the middle of the brain, between the two hemispheres.

  • The pineal gland is a neuroendocrine secretory circumventricular organ with capillaries that are largely permeable to blood solutes.

  • Melatonin production is the pineal gland’s primary role. Melatonin functions in the central nervous system in a variety of ways, the most important of which is to help regulate sleep patterns. Darkness stimulates melatonin development, while light inhibits it.

  1. Thyroid Gland

  • The thyroid gland is a two-lobed endocrine gland in the neck that produces thyroid hormone.

  • A thin band of tissue called the thyroid isthmus connects the lower two-thirds of the lobes.

  • The thyroid gland is found below Adam’s apple in the front of the neck.

  • The spherical thyroid follicle, lined with follicular cells (thyrocytes) and occasional parafollicular cells that surround a lumen containing colloid, is the functional unit of the thyroid gland.

  • The thyroid gland produces three hormones: triiodothyronine (T3) and thyroxine (T4) are the two thyroid hormones that are created from iodine and tyrosine, and calcitonin, a peptide hormone.

  • Thyroid hormones affect metabolic rate and protein synthesis, as well as growth and development in infants.

  • Calcium homeostasis is supported by calcitonin.

  • Thyroid hormones modulate DNA transcription by crossing the cell membrane and binding to nuclear thyroid hormone receptors TR-ɑ1, TR-ɑ2, TR-β1, and TR-β2, which bind with hormone response elements and transcription factors.

  • Thyroid hormones also function within the cell membrane or cytoplasm through reactions with enzymes such as calcium ATPase, adenylyl cyclase, and glucose transporters, in addition to their actions on DNA.

  1. Parathyroid Gland

  • Humans and other tetrapods have tiny endocrine glands in their necks called parathyroid glands.

  • Humans have four parathyroid glands, which are normally found on the back of the thyroid gland in different places.

  • In response to low blood calcium, the parathyroid gland produces and secretes the parathyroid hormone, which plays an important role in controlling the amount of calcium in the blood and bones.

  • The primary function of the parathyroid glands is to keep calcium and phosphate levels in the body within a small range so that the nervous and muscular systems can work properly. This is accomplished by the parathyroid glands secreting parathyroid hormone (PTH).

  1. Thymus Gland

  • The immune system’s thymus is a specialized primary lymphoid organ. Thymus cell lymphocytes or T cells grow within the thymus. 

  • T cells play a crucial role in the adaptive immune system, which allows the body to respond to foreign invaders. 

  • The thymus is found in the anterior superior mediastinum, behind the sternum, and in front of the heart in the upper front portion of the chest. 

  • It consists of two lobes, each with a central medulla and an outer cortex, and is encased in a capsule.

  1. Adrenal Gland

  • The adrenal glands, also known as suprarenal glands, are endocrine glands that contain adrenaline and the steroids aldosterone and cortisol, among other hormones. Above the kidneys are the adrenal glands.

  • An outer cortex that produces steroid hormones and an inner medulla make up each gland. The zona glomerulosa, zona fasciculata, and zona reticularis are the three major areas that make up the adrenal cortex.

  1. Pancreas

  • The pancreas is a digestive and endocrine system organ found in the vertebrates.

  • The pancreas is the largest endocrine gland in the human body.

  • It is a gland that is found in the abdomen behind the stomach in humans.

  • The pancreas performs both endocrine and digestive exocrine functions. It is an endocrine gland that regulates blood sugar levels by secreting the hormones insulin, glucagon, somatostatin, and pancreatic polypeptide.

  • It works as an exocrine gland in the digestive system, secreting pancreatic juice into the duodenum through the pancreatic duct.

  1. Gonads

  • A gonad, also known as a sex gland or reproductive gland, is a mixed gland that contains an organism’s gametes (sex cells) and sex hormones.

  • Two key hormones are released by the female ovaries, which are found in the pelvic cavity. Under the influence of follicle-stimulating hormone, the ovarian follicles begin to secrete estrogens at puberty.

  • Estrogens promote the production of secondary sexual characteristics and the maturation of the female reproductive system. Progesterone is produced in response to high luteinizing hormone levels in the blood. It helps to regulate the menstrual cycle by interacting with estrogens.

  • In response to luteinizing hormone, the male testes begin to release testosterone at puberty.

  • Testosterone aids in the maturation of male reproductive organs, as well as the development of secondary sex characteristics such as increased muscle and bone mass and hair growth.

The human endocrine system diagram given below shows all glands in the human body (Male and Female).

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Endocrine System Hormones

In this section, we will learn about all hormones in the human body which are secreted by endocrine glands.

  1. Adrenaline

  • Adrenaline known as epinephrine is secreted by the adrenal gland.

  • Adrenaline’s main effects involve rising heart rate, blood pressure, widening lungs for air passage, enlarging the pupil in the eye, redistributing blood to muscles, and changing the body’s metabolism to maximize blood glucose levels, mainly for the brain.

  1. Aldosterone

  • Aldosterone is a steroid hormone secreted by the adrenal gland.

  • The primary function of aldosterone is to control salt and water in the body, thus influencing blood pressure.

  1. Cortisol

  • Cortisol is a steroid hormone secreted by the adrenal gland.

  • Cortisol controls a variety of vital functions in the body, including metabolism and immune response. It also plays a vital role in assisting the body’s stress response.

  1. Dehydroepiandrosterone Sulfate (DHEA)

  • Dehydroepiandrosterone sulfate (DHEA) is secreted by the adrenal gland.

  • DHEA is a male sex hormone that both men and women produce. DHEA is required for the production of both the male and female sex hormones testosterone and oestrogen. It also plays a role in the maturation of male sexual characteristics during puberty.

  1. Estrogen

  • Estrogen is secreted by the ovaries in females.

  • Estrogens are involved in ovarian function, such as the maturation of ovarian follicles, as well as vaginal and uterus maturation and maintenance. Estrogens also play a key role in the regulation of gonadotropin secretion. 

  1. Follicle Stimulating Hormone (FSH)

  • The pituitary gland secretes Follicle Stimulating Hormone (FSH).

  • FSH aids in the regulation of the menstrual cycle in women and promotes the development of eggs in the ovaries. Women’s FSH levels fluctuate during the menstrual cycle, with the maximum levels occurring right before the ovary releases an egg. This is referred to as ovulation. FSH aids in the regulation of sperm production in males.

  1. Glucagon

  • Glucagon is secreted by the pancreas.

  • Glucagon induces glucose synthesis, prevents glucose degradation, and facilitates the conversion of glycogen to glucose in the liver.

  1. Insulin

  • The ꞵ cells of the pancreatic islets of Langerhans secrete the peptide hormone called Insulin.

  • Insulin regulates blood glucose levels by facilitating cellular glucose absorption, controlling carbohydrate, lipid, and protein metabolism, and promoting cell division and growth through its mitogenic effects.

  1. Luteinizing Hormone (LH)

  • The pituitary gland secretes Luteinizing hormone (LH).

  • LH is important for sexual development and function. LH aids in the regulation of the menstrual cycle in women. It also causes an egg to be released from the ovary. This is referred to as ovulation.

  1.  Melatonin

  • Melatonin is secreted by the pineal gland.

  • Melatonin is a hormone of darkness that mediates dark signals and provides night information, rather than being a sleep hormone. It’s also thought to be an endogenous synchronizer, stabilising and reinforcing the body’s various circadian rhythms.

  1.  Oxytocin

  • Oxytocin is secreted by the pituitary gland.

  • The function of oxytocin in female reproduction is well-known. It is released in significant quantities during labour and after nipple stimulation. The use of oxytocin as a medicinal agent during labour and childbirth is one of the oldest uses of oxytocin as a medicine.

  1.  Parathyroid hormone

  • Parathyroid hormone is secreted by the Parathyroid gland.

  • The parathyroid hormone causes the bones to release calcium into the bloodstream, the intestines to absorb calcium from food, and the kidneys to conserve calcium.

  1.  Progesterone

  • The corpus luteum in the ovary secretes the Progesterone hormone.

  • Progesterone is important for sustaining the early stages of pregnancy and the menstrual cycle. It may also play a role in the progression of some cancers.

  1.  Prolactin

  • Prolactin is secreted by the pituitary gland.

  • Prolactin is involved in hundreds of physiologic activities, but two of the most important are milk production and the growth of mammary glands in breast tissues. Prolactin encourages the development of mammary alveoli, which are the components of the mammary gland where milk is produced.

  1.  Testosterone

  • Testosterone is secreted by multiple glands, ovaries, testes and adrenal.

  • Testosterone is a sex hormone with many functions in the body. It’s thought to control libido, bone density, fat distribution, muscle mass and strength, and red blood cell and sperm production in men. A small amount of testosterone in the bloodstream is transformed into estradiol, an estrogen-like substance.

  1.  Thyroid hormone

  • The thyroid gland secretes the thyroid hormone.

  • Thyroid hormones have an effect on every cell and organ in the body. They influence weight loss or benefit by regulating the rate at which calories are burned. The heartbeat can be slowed or sped up by thyroid hormone.

Conditions Affecting the Human Endocrine System

  • When our thyroid gland produces more thyroid hormone than is needed, we will have hyperthyroidism. A variety of factors, including autoimmune diseases, can cause this.

  • When our thyroid does not produce enough thyroid hormone, we will have hypothyroidism. It can be caused by a variety of factors, much like hyperthyroidism.

  • High levels of the hormone cortisol cause Cushing syndrome.

  • When our adrenal glands don’t produce enough cortisol or aldosterone, we get Addison disease.

  • Diabetes is a disorder in which the blood sugar levels are uncontrollably high. Diabetes patients have an excessive amount of glucose in their blood (high blood sugar). Type 1 diabetes and type 2 diabetes are the two forms of diabetes.

In this article, we studied different glands of the human endocrine system, also we got to know the master gland and largest endocrine gland in the human body, hormones in the human body, and the conditions which affect the human endocrine system.


The endocrine system is a complex system of glands and organs that aids in the regulation of many bodily functions. This is achieved by the endocrine system’s release of hormones, or chemical messengers. The endocrine system consists of glands that generate and secrete hormones, which are chemical compounds generated in the body that control cell or organ function. Hormones control body growth, metabolism (the body’s physical and chemical processes), and sexual development and function. Hormones are released into the bloodstream and have the potential to affect one or more organs in the body.

Human endocrine system – Coordination and control – The human endocrine system – Edexcel – GCSE Biology (Single Science) Revision – Edexcel

Hormones and nerves

A hormone is a chemical substance, produced by a gland and carried in the bloodstream, which alters the activity of specific target organs. An example of this is the release of the hormone adrenaline, which is released by the adrenal glands. One of its target organs is the heart, where it increases the heart rate.

Once a hormone has been used, it is destroyed by the liver.

Like the nervous system, hormones can control the body. The effects are much slower than the nervous system, but they last for longer.

Contraceptive pills contain hormones to reduce the chances of becoming pregnant

There are important differences between nervous and hormonal control.

Nervous Hormonal
Type of signal Electrical (chemical at synapses) Chemical
Transmission of signal By nerve cells (neurones) By the bloodstream
Effectors Muscles or glands Target cells in particular organs
Type of response Muscle contraction or secretion Chemical change
Speed of response Very rapid Slower
Duration of response Short (until nerve impulses stop) Long (until hormone is broken down)

Different hormones

The glands in the body produce a range of different chemical hormones that travel in the bloodstream and affect a number of different organs in the body. The diagram below shows this in detail.

Important hormones released into the bloodstream include ADH (anti-diuretic hormone), adrenaline and insulin.

Hormone Source Target organ(s) Role Effects
ADH Pituitary gland Kidneys Controlling the water content of the blood Increases reabsorption of water by the collecting ducts
Adrenaline Adrenal glands Several targets including organs in the respiratory and circulatory systems Preparation for ‘fight or flight’ Increases breathing rate, heart rate, flow of blood to muscles, conversion of glycogen to glucose
Insulin Pancreas Liver Controlling blood glucose levels Increases conversion of glucose into glycogen for storage

Master gland

The pituitary gland in the brain is known as a ‘master gland’. It secretes several hormones into the blood in response to the body’s condition, such as blood water levels. The hypothalamus detects changes in hormone levels and will release hormones which control the pituitary gland or other organs. The hormones from the hypothalamus and pituitary can also act on other glands to stimulate the release of different types of hormones and bring about effects.

The thyroid gland

What is the thyroid gland?

The thyroid gland is a key part of the human endocrine system and works together with your nervous and immune systems to regulate your body’s metabolism.

Metabolism refers to all of the processes that go on inside your body, for example, the process of turning food into energy.

The thyroid gland regulates metabolism by producing and secreting hormones into your bloodstream.

Terms explained

Autoimmune disorder – a condition where your own antibodies attack your body.

Where is the thyroid gland?

The thyroid gland is located in the lower front part of your throat, just below your Adam’s apple. It consists of 2 lobes on either side of your windpipe.

What does the thyroid gland do?

Your thyroid produces 2 important hormones:

  • Thyroxine, known as T4
  • tri-iodothyronine, known as T3.

Thyroid hormones affect your:

  • body temperature and circulation
  • appetite
  • energy levels
  • growth and bone development
  • muscle tone and suppleness
  • heart rate
  • blood sugar levels
  • central nervous system and bowel function
  • cholesterol levels
  • fat, carbohydrate and protein metabolism.

Thyroid hormones and metabolism

Your thyroid controls the chemical metabolic processes constantly taking place inside your body. This process of metabolism is how your body gets the energy it needs to survive and has a vital function.

Your body needs iodine to make thyroid hormones. Most people get suitable amounts of iodine from their diet as it is found in most food, especially seafood. Small amounts of iodine are found in vegetables grown in soils containing iodine.

If your thyroid cannot produce a sufficient amount of hormones you are vulnerable to a range of serious health conditions.

The higher the T3 and T4 iodine count that circulates in your blood the faster your metabolism is. If you have less T3 and T4, your metabolism levels drop.

If your thyroid becomes overactive (hyperthyroidism), or underactive (hypothyroidism) it is not performing normally and starts to produce abnormal chemical reactions in your body leading to:

  • disruption of your entire metabolic system
  • unusually high or low levels of hormones or enzymes
  • malfunctioning hormones or enzymes
  • a build-up of toxic substances in your body
  • diseases and serious health conditions.

Your pituitary and thyroid glands

The pituitary is an endocrine gland located at the base of your brain that controls your endocrine system, including your thyroid. The pituitary affects the thyroid by producing a hormone called thyroid stimulating hormone (TSH).

TSH causes cells within your thyroid to make more T3 and T4 hormone.

If there is too much T4 in your bloodstream your pituitary produces less TSH, which causes your thyroid activity to slow. If there is not enough T4 hormone the pituitary increases the amount of TSH to help speed up your metabolism.


A goitre is when your thyroid gland becomes significantly swollen and enlarged – this can happen if your diet is low in iodine.

If you are iodine deficient your pituitary gland may try to compensate by overstimulating your thyroid to produce more thyroid hormone. When this happens your thyroid grows larger and larger.

The presence of goitre in your neck suggests your thyroid is not functioning properly or you are iodine deficient.

Other thyroid gland disorders

Several disorders are associated with the thyroid gland:

  • Graves’ disease
  • Hashimoto’s disease
  • thyroid cancer
  • thyroid nodules
  • congenital thyroid disease
  • iodine deficiency disorder.

Hyperthyroidism – overactive thyroid

Hyperthyroidism is a condition where your thyroid is overactive and releases too many T4 and T3 hormones into your bloodstream, creating a hormonal imbalance and causing your metabolism to speed up.

The most common cause of hyperthyroidism is an autoimmune condition called Graves’ disease.

Learn more about hyperthyroidism, including Graves’ disease and the symptoms and treatment of an overactive thyroid.

Hypothyroidism – underactive thyroid

Hypothyroidism is a condition where your thyroid is underactive and releases too little T4 and T3 hormones into your bloodstream.

This causes your metabolism to slow down too much and reduces the thyroid’s ability to make hormones.

The most common cause of hypothyroidism is an autoimmune condition called Hashimoto’s disease.

Learn more about hypothyroidism, including Hashimoto’s disease and the symptoms and treatment of an underactive thyroid.

Where to get help

  • See your doctor
  • See your endocrinologist
  • Visit a GP after hours
  • Ring healthdirect Australia on 1800 022 222.


  • People with a family history of thyroid conditions have a higher risk of also getting thyroid and other autoimmune conditions.
  • An overactive thyroid (hyperthyroidism) releases too much T4 and T3 into your blood stream and causes your metabolism to speed up.
  • An underactive thyroid (hypothyroidism) does not release enough T4 and T3 into your blood stream and causes your metabolism to slow down too much.
  • Thyroid conditions can be treated and have a good prognosis.
  • Thyroid conditions affect more women than men.


Diabetes and Endocrine Health Network

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

Chemical Exposures and Our Endocrine System

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The human endocrine system produces hormones that help regulate bodily functions, including metabolism, growth, development, tissue function, sexual function, reproduction, sleep and mood. Made up of the pituitary, thyroid, parathyroid and adrenal glands, as well as the pancreas, ovaries (in females) and testicles (in males), the endocrine system is at work virtually all the time. Our bodies rely on hormones to manage many normal daily functions, as well as ongoing growth and developmental changes throughout our lives.

Given the importance of endocrine activity to our overall health, it’s understandable that readers may become concerned by posts on popular social media sites that claim exposures to some chemicals may have lasting health impacts on their body.

The terms “endocrine-disrupting chemical” or “hormone-disrupting chemical” are widely misused and considered by scientists to be a misnomer, since many substances have been shown to interact with the endocrine system without causing an adverse health effect. Many things we come in contact with, such as sunlight, or common substances, such as caffeine, can “activate” the endocrine system. Some of these interactions are harmless. Others are helpful — like when exposure to sunlight causes our bodies to produce Vitamin D.


What is an endocrine disruptor?

In order for a chemical to be an “endocrine disruptor,” it must affect the endocrine system in a way that causes a negative health effect. It’s important to distinguish endocrine activity that is disruptive or damaging, from endocrine activity that is neutral or even essential to our well-being.

Not all chemicals that interact with the endocrine system present a risk of harm – in many instances, the body naturally adjusts and there is no health effect. For example, when we drink a soy latte or eat edamame, our estrogen levels will become slightly elevated, and then return to normal after a short time. Just because a substance is endocrine active does not mean that it is endocrine disruptive.

So how do we look beyond the headlines, to understand the science? Some chemicals, both natural and man-made, can and do interact with the endocrine system. There is confusion as to whether this interaction is itself harmful, or if the endocrine activity could lead to harm if exposure is above a certain level or frequency.

The two articles on the right explore 1) the science of how our bodies are exposed to and metabolize substances, as well as 2) public policy developments – how government regulators study and screen substances to understand if they might be endocrine active or endocrine disrupting.

The goal is to enable regulators to use science to reasonably assess real-life risk – the possibility of harm arising from a particular exposure to a specific chemical, under typical conditions. In doing so, scientists can help provide informed and confident recommendations to regulatory decision-makers about how chemical ingredients can be safely used as a part the products and materials in our everyday lives.

How Do Chemicals Impact the Endocrine System? Learn more here.

Hormones: Definition, Function & Intro to the Endocrine System – Video & Lesson Transcript

What Are Hormones?

Hormones are actually tiny chemical messengers located inside of your body. They are unable to be seen with the human eye and travel throughout the internal superhighway – otherwise known as the bloodstream – to all of your body’s organs and tissues. Different hormones perform specific roles inside of your body. Some of these hormones work quickly to start or stop a process, and some will continually work over the course of a long period of time to perform their necessary jobs. Some of these jobs include the body’s growth and development, metabolism (or production of energy), sexual function and reproduction.

The Endocrine Glands

The endocrine glands are a highly specialized group of cells responsible for making hormones. These glands are located throughout your entire body. Each gland plays a specific role in the production of a particular hormone or group of hormones needed to carry out the necessary duties required by your body to help the body remain in a state of homeostasis, or continual balance. The body requires a continual state of balance in order to function at its maximum level of efficiency. If, for any reason, your body is ever found to be outside of homeostatic balance, there could be significant negative results if the body is not repaired within a certain period of time.

For example, if a person is exposed to cold weather for an extended period of time, the body’s internal temperature begins to fall. The body’s temperature must remain within a certain range in order for the continual balance of homeostasis to occur and ensure all organs and systems are functioning properly. In order to remain in homeostatic balance, certain hormones are sent to specific cells and tissues to trigger a sensation which generates heat within the body and causes you to experience things such as shivering and the chattering of your teeth. These indications remind you that it is time to find a warmer location so your body may begin working to restore its internal temperature back to the range needed for proper body functions to occur. If the body temperature continues to fall, and you are unable to find a way to generate the heat required to reverse this problem, organs and systems will slowly begin to fail.

Hormones bind to receptor sites on the targeted tissues or cells.

The endocrine glands and their related organs operate like small factories. They produce and store the gland-specific hormones until the time comes for those hormones to be released to a particular site in the body. The specific endocrine gland will receive a message from the pituitary gland, which is also known as the master gland, stating how much hormone is needed and where this hormone is to travel. The hormone then begins its journey through the superhighway of the bloodstream and continues along this path until it reaches the targeted tissues or cells. These tissues and cells will contain receptors located along their outside walls to serve as binding sites for the attachment of the hormone. Once the hormone has attached to one of the binding sites, the hormone is now in a position to carry out its specific role in helping maintain your body’s homeostatic balance.

Location of the Endocrine Glands

When we visualize the human body, starting with the head, we can locate the pituitary gland and pineal gland inside of the brain. The pituitary gland is normally found inside of the skull, just above the nasal passages. It is considered the master gland because of its responsibility to ensure the timely production and delivery of every hormone in the body. Its assistant, the hypothalamus, while not officially considered a major endocrine gland, serves an essential role in helping with the delivery of messages to and from each respective endocrine gland throughout the body. This relationship controls the amount of hormone secreted from various glands during a particular period of time. The hypothalamus is actually located quite close to the pituitary, sitting directly above the brain stem. The pineal gland is a small, pea-sized gland located towards the back portion of the brain and is responsible for your body’s circadian rhythm, or internal clock.

The thyroid and parathyroid glands are located at the base of your neck. The parathyroid glands are actually directly behind the thyroid glands, but both of these glands together resemble a bowtie-shape. The thyroid gland’s main function is to control your body’s metabolism, while the parathyroid glands play a large role in the distribution of calcium and phosphate throughout the body.

The pancreas is located behind the stomach and produces insulin and glucagon.

The pancreas lies directly behind the stomach and is responsible for the production of insulin and glucagon. Both insulin and glucagon are important in helping maintain the correct level of glucose in your body throughout the day, especially before and after you eat. The adrenal glands resemble witches’ hats and sit on top of each kidney. They are responsible for the fight-or-flight reflex your body enters when faced with a challenging or frightening situation. They also play a large role in the anti-inflammatory response as well as the regulation of salt and water balance within your body.

In males, the testes are located outside of the pelvic cavity and are responsible for the production of male sex organs and secondary sexual characteristics, such as extra muscle development, lowering of the voice and increased body hair. In females, the ovaries are located inside of the pelvic cavity on either side of the uterus and are responsible for the production of eggs, which are needed for reproduction. Also, the ovaries are responsible for female secondary sex characteristics, such as breast enlargement and changes in the physical shape of a woman’s body.

Lesson Summary

As you can see, the hormones and endocrine system are quite complex and their work is never done. The endocrine system has a large responsibility for producing enough hormones and ensuring there are ample amounts stored for the proper delivery to all needed cells and tissues within your body. These hormones are a vital part of the body’s composition and play a significant role in the body’s daily functions. Without adequate amounts, you would have problems with general functions as well as long-term issues due to the inability of your body to keep itself in a state of homeostasis.

Learning Outcomes

At the end of this lesson, you’ll be able to:

  • Describe the importance and functions of hormones and the endocrine glands in general
  • Identify the locations of many endocrine glands and understand their specific functions
  • Examine the journey hormones take from an endocrine gland to the receptor sites where they are needed

90,000 Online lesson: Human endocrine system in the subject of Biology, grade 8

In the very first organisms, bacteria , the rudiments of humoral regulation are observed, that is, you can notice the release of substances by the bacterial cell in response to changing environmental conditions.

The endocrine system emerged from neurosecretory neurons , which can be found already in coelenterates (hydras, jellyfish), they are found in more developed invertebrates and all vertebrates.

Previously, the secretion of substances, including mediators, was performed by nerve cells, which in the process of evolution separated into separate – endocrine .

In some species flatworms neurosecretory cells regulate the water-salt balance, and epithelial cells are able to secrete sex hormones.

Endocrine glands appear for the first time in annelids.

crustaceans have Y-organs at the front end of the body that activate the molting process.

These glands are under the control of X-organs, which are closely interconnected with the head nerve nodes.

Also in the eyes of crustaceans there are sinus glands that regulate metamorphosis.

In insects , at the front end of the body there are endocrine glands that control metamorphosis and regulate energy metabolism.

These glands are regulated by the endocrine gland in the head, which is under the control of the cephalic ganglion.

In vertebrates , in addition to six separate endocrine glands, hormones are produced in some organs along with other functions – these are the gonads, pancreas, heart and digestive tract cells.

Vertebrates under the scalp or deep in the brain have pineal gland , which functions as a light-receiving organ or as an endocrine gland whose activity depends on illumination.

In some animals, both of these functions are combined.

In vertebrates the thyroid gland in phylogeny develops from the epithelium of the pharynx. Initially, this gland was laid as an external secretion gland.

In fish , it looks like a single strand and arises between the first and second branchial slits, and in other vertebrates between the second and third branchial pockets.

During phylogenesis in vertebrates, the thyroid gland changes its location, and, starting from amphibians , separate lobules and an isthmus appear in it.

Thymus in fish grows from the epithelial protrusions of the branchial pockets, which later separate and form two narrow strips of lymphoid tissue with a lumen inside.

In amphibians and reptiles the thymus originates from the second and third pairs of branchial pockets, in mammals from the second pair of branchial pockets.

The pituitary gland in terrestrial vertebrates consists of three lobes: anterior, middle (intermediate) and posterior.

And in fish only from the front and middle.

The pituitary gland grows together with the lower surface of the diencephalon, and in the process of ontogenesis develops from different sources: the anterior and middle lobes from the epithelium of the oral cavity, and the posterior lobe from the diencephalon.

The function of the pituitary gland in fish is realized in the production of gonadotropic hormones.

In amphibians , the posterior lobe of the pituitary gland appears in connection with the transition to a terrestrial lifestyle and the need to regulate water exchange.

In the posterior lobe of the pituitary gland of amphibians, the axons of the hypothalamic neurons are located, which accumulate antidiuretic hormone .

The average share in amphibians produces a hormone that stimulates melanin synthesis .

In terrestrial vertebrates, the anterior lobe, in addition to gonadotropin, secretes other tropic hormones, as well as growth hormone .

The adrenal glands in chordates are formed from the epithelium of the peritoneum and are located above the superior pole of the kidneys.

In amphibians there is a spatial connection between the adrenal glands, and in higher vertebrates the adrenal anlages merge, forming a paired organ, consisting of the external cortical and internal medulla.

Sex hormones in animals are produced in the genitals: testes (in males) and ovaries (in females).

Sex glands , or gonads – testes ( testicles ) and ovaries are among the glands with mixed secretion.

External secretion is associated with the formation of male and female germ cells: spermatozoa and eggs .

Intrasecretory function is the secretion of male and female sex hormones and their release into the blood.

Sex hormones contribute to the development of genital organs in ontogenesis and the appearance of secondary sexual characteristics during puberty, and also determine the behavior of organisms.

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 the deaf-blind, which gives people who are 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.

In the hall there are excursions “Who is the head of everything” for junior schoolchildren, “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.

Endocrine diseases

Diabetes insipidus


Thyroid cyst

Diabetes mellitus – type 1


Myasthenia gravis

Endocrinology is a field of medicine that studies the structure and functioning of the endocrine glands, which in turn produce hormones that are vital for humans.Various stresses, environmental degradation, as well as heredity factors can disrupt the normal functioning of the endocrine glands, which leads to endocrine diseases.

If you are obese, you have had people in your family who had endocrine diseases, for example, diabetes mellitus, or you have noticed symptoms such as sweating, increased heart rate, fatigue or dry skin, then in this case you are advised to consult a doctor- endocrinologist for consultation.

Most likely, you will have to undergo a diagnostic examination, which includes: the delivery of tests for the content of various hormones, a patient survey, MRI, ultrasound. Hormones play an important role in the daily life of a person, because they control factors such as: growth, metabolism, reproduction and puberty. Therefore, it is necessary to identify any irregularities in the functioning of the endocrine glands as early as possible and prevent possible complications.

Diabetes insipidus

What is it? Diabetes insipidus is an endocrine disease associated with dysfunction of the pituitary gland and / or hypothalamus.It is rare: there are 3 cases of the disease per 100,000 people with the same frequency in men and women. The age of the sick is from 25 to 50 years.

Why does diabetes insipidus develop, and what is it? One of the functions of the hypothalamus is to regulate the secretion of two important hormones: oxytocin and vasopressin (antidiuretic hormone). The main role of the latter hormone is the reabsorption (resorption) of water by the kidneys. The place of temporary storage of hormones after their secretion is the pituitary gland.It is from it that vasopressin and other hormones are released into the bloodstream as needed. Deficiency of vasopressin is accompanied by impaired absorption of water in the kidneys, which leads to the manifestation of symptoms of the disease, reminiscent of the symptoms of diabetes mellitus, which is also characterized by diabetes, thirst. Another cause of diabetes insipidus is the immunity of kidney tissue to the effects of this hormone.


What is it – thyrotoxicosis is considered one of the most common diseases of the thyroid gland.This disease is characterized by an increased work of the thyroid gland, which produces too many hormones. Such a pathology leads to the malfunction of many organs and systems of the body, and also adversely affects the state of the thyroid gland itself. Thyrotoxicosis is the opposite of hypothyroidism, in which the production of hormones, on the contrary, slows down.

Thyroid cyst

Thyroid cyst is a hollow formation surrounded by a capsule with a liquid content in most cases of a benign nature.In other words, it is a vesicle, the walls of which are lined with fluid-producing epithelium. Of all endocrinological diseases, about 3-5% are caused by thyroid cysts.

Diabetes mellitus – type 1

Diabetes mellitus is often called the epidemic of the 20th century. The accelerated pace of life, stress, unhealthy diet and a sedentary lifestyle provoke a disease in which the endocrine system cannot cope with its functions. The body is unable to process carbohydrates because there is not enough insulin, a hormone in the pancreas.The hormone helps convert glucose and other nutrients into life energy. If there is not enough insulin, a failure occurs throughout the body. The patient loses activity, weakness appears, sleep is disturbed, kidneys and neurovascular system suffer.


What is it – until recently, gynecomastia was considered a fairly rare disease. However, as statistics show, recently the number of men who suffer from this ailment has increased significantly.The very term “gynecomastia” came to us from the Greek language, where it means two words “breast” and “woman”. Modern medicine defines the concept of gynecomastia as a disease associated with excessive enlargement of the mammary glands in the male population. This pathology can have various causes. Thus, the treatment is selected based on the etiology of the disease and the individual characteristics of the patient.

Myasthenia gravis

What is it? Myasthenia gravis is a classic autoimmune disease characterized by impaired transmission of excitation at the level of the neuromuscular synapse, manifested by pathological lack of strength, fatigue of mainly skeletal muscles designed to perform various actions.The danger of the disease lies in the development of critical conditions – myasthenic crises, which can be fatal. Although it should be said that modern methods of diagnosis and treatment have minimized the percentage of mortality, and most patients achieve stable remission.

Human endocrine system | Endocrine glands and their hormones (table)

Endocrine system functions

Maintaining homeostasis in the body requires the coordination of many different systems and organs.

One of the mechanisms of communication between neighboring cells , as well as between cells and tissues in distant parts of the body, is interaction through the release of chemicals called hormones , which are produced by the endocrine system .

Hormones are released into body fluids, usually blood. The blood carries them to target cells, where hormones trigger the desired response.

Hormone-secreting cells are often located in specific organs called endocrine glands .

The cells, tissues and organs that secrete hormones make up the endocrine system .

Some of the regulatory functions of the endocrine system include:

  • heart rate control ,
  • blood pressure control ,
  • control immune response to infection,
  • regulation of the processes of reproduction , growth and development organisms,
  • level regulation emotional state .

Endocrine glands

The endocrine system consists of:

Many other organs, such as liver , skin , kidney and parts of the digestive and circulatory systems , produce hormones in addition to their basic specific physiological functions.

Endocrine glands ( endocrine glands ) are glands that release hormones directly into the bloodstream through blood vessels passing through them, while exocrine glands release their secretions through ducts or tubes.

Examples of exocrine glands are sweat glands , salivary glands and lacrimal glands .

Types of hormones – steroid and non-steroidal hormones and their mechanisms of action

The endocrine system produces two main types of hormones:

  1. Steroid hormones
  2. Non-steroidal hormones

Steroid hormones

Steroid hormones , such as cortisol, are made from cholesterol .

Each type of steroid hormone consists of a central structure of four carbon rings with different side chains attached to them, which determine the specific and unique properties of the hormone.

Inside endocrine cells, steroid hormones are synthesized in smooth endoplasmic reticulum .

Since steroid hormones are hydrophobic , they bind to a protein carrier that carries them through the bloodstream.

Fat-soluble steroid hormones can pass through the membrane of the target cell.

Inside the target cell in the cytoplasm, steroid hormones bind to the receptor protein molecule. This hormone-receptor complex then enters the nucleus, where it binds and activates a specific gene on the DNA molecule.

The activated gene then produces an enzyme that initiates the desired chemical reaction within the cell.

Non-steroidal hormones

Non-steroidal hormones , such as epinephrine, are composed of either proteins, peptides or amino acids.

These hormone molecules are not fat-soluble, so they usually cannot penetrate into the cell through the plasma membrane in order to exert their effect.

Instead, they bind to receptors on the surface of target cells. This binding to receptors then triggers a specific chain of chemical reactions within the cell.

Hormones of the human endocrine glands and their functions

Endocrine gland Hormones Hormonal effect

Pituitary gland

Pituitary gland, (anterior lobe (adenohypophysis)) growth hormone promotes the growth of body tissues
Pituitary (anterior) prolactin promotes milk production
thyroid-stimulating hormone stimulates the secretion of thyroid hormones
adrenocorticotropic hormone stimulates the secretion of hormones by the adrenal cortex
follicle-stimulating hormone stimulates gamete production
luteinizing hormone stimulates the production of androgens by gonads in men;
stimulates ovulation and the production of estrogen and progesterone in women
Pituitary gland, (posterior lobe (neurohypophysis)) antidiuretic hormone stimulates renal water reabsorption
Pituitary (posterior) oxytocin stimulates uterine contractions during labor


Thyroid thyroxine, triiodothyronine stimulates metabolism
Thyroid calcitonin reduces the level of Ca 2+ in the blood

Parathyroid glands


parathyroid hormone (parathyroid hormone) increases the level of Ca 2+ in the blood

Adrenal glands

Adrenal gland (cortex) aldosterone increases the level of Na + in the blood
Adrenal (cortex) cortisol,
raises blood glucose

Adrenal gland (medulla)

Adrenal (medulla)

stimulates the fight-or-flight response


Pancreas insulin lowers blood glucose
Pancreas glucagon raises blood glucose

Pineal gland

Pineal gland

Pineal gland

melatonin regulates the body’s circadian rhythms


Thymus gland (thymus)

Thymus gland

thymosin stimulates the production and maturation of lymphocytes

Endocrine system, preparation for the exam in biology

Endocrinology (from the Greek.ἔνδον – inside, κρίνω – I highlight and λόγος – word, science) – the science of humoral (from Latin humor – moisture)
regulation of the body, carried out with the help of biologically active substances: hormones and hormone-like compounds.

Endocrine glands

The secretion of hormones into the blood occurs by the endocrine glands (IVS), which do not have excretory ducts, and also
endocrine part of the glands of mixed secretion (YSS).

I would like to draw your attention to the YSS: pancreas and gonads.We have already studied the pancreas in the section
digestive system, and you know that its secret – pancreatic juice, takes an active part in the process
digestion. This part of the gland is called exocrine (Greek exo – outside), it has excretory ducts.

The sex glands also have an exocrine portion that contains ducts. The testicles secrete seminal fluid with sperm into the ducts, the ovaries – eggs. This “exocrine” digression is necessary to clarify
and rightfully begin the study of endocrinology – the science of life-saving drugs.


The pituitary gland, pineal gland, thyroid gland, parathyroid glands, thymus (thymus gland),
adrenal glands.

ZhVS release hormones into the blood – biologically active substances that have a regulatory effect on metabolism and physiological functions. Hormones have the following properties:

  • Distant action – far from the place of its formation
  • Specific – affect only those cells that have hormone receptors
  • Biologically active – have a pronounced effect at a very low concentration in the blood
  • They are rapidly destroyed, as a result of which they must be constantly excreted by the glands
  • Not species specific – hormones of other animals cause a similar effect in the human body

By their chemical nature, hormones are divided into three main groups: protein (peptide), amino acid derivatives and
steroid hormones made from cholesterol.

Neurohumoral regulation

The physiology of the body is based on a single neurohumoral mechanism for the regulation of functions: that is, control is carried out both by the nervous system and by various substances through the body’s fluids. Let us analyze the function of respiration, as an example of neurohumoral

With an increase in the concentration of carbon dioxide in the blood, the neurons of the respiratory center in the medulla oblongata are excited, which increases
the frequency and depth of breathing.As a result, carbon dioxide begins to be more actively removed from the blood. If the concentration of carbon dioxide in the blood
falls, then an involuntary decrease and decrease in the depth of breathing occurs.

An example of neurohumoral regulation of respiration is far from the only one. The relationship between nervous and humoral regulation is so close
that they are combined into a neuroendocrine system, the main link of which is the hypothalamus.


The hypothalamus is a part of the diencephalon, its cells (neurons) have the ability to synthesize and secrete special substances,
having hormonal activity – neurosecrets (neurohormones).The secretion of these substances is due to the effect on the receptors of the hypothalamus
a wide variety of blood hormones (the humoral part has begun), pituitary gland, glucose and amino acid levels, blood temperature.

That is, the neurons of the hypothalamus contain receptors for biologically active substances in the blood – hormones of the endocrine glands, when
the level of which changes the activity of neurons in the hypothalamus. The hypothalamus itself is represented by nerve tissue – this is a section of the diencephalon.Thus, it surprisingly combined two mechanisms of regulation: nervous and humoral.

Closely related to the hypothalamus is the pituitary gland, the “conductor of the orchestra of the endocrine glands,” which we will explore in detail in the next article. Between
the hypothalamus and pituitary gland have a vascular connection, as well as a nervous one: some hormones (vasopressin and oxytocin) are delivered from
the hypothalamus into the posterior lobe of the pituitary gland along the processes of nerve cells.

Remember that the hypothalamus secretes special hormones – liberins and statins.Liberins or releasing hormones (Latin libertas –
freedom) promote the formation of hormones by the pituitary gland. Statins or inhibitory hormones (Latin statum –
stop) inhibit the formation of these hormones.

© Bellevich Yuri Sergeevich 2018-2021

This article was written by Yuri Sergeevich Bellevich and is his intellectual property. Copying, distribution
(including by copying to other sites and resources on the Internet) or any other use of information and objects
without the prior consent of the copyright holder is prosecuted.To obtain the materials of the article and permission to use them,
please refer to Bellevich Yuri .

90,000 Invitro. Hormonal research, find out the prices for tests and pass in Moscow

Placental lactogen (HPL)

Peptide hormone produced by the placenta during pregnancy. Diagnostic test for determining the state of the placenta, identifying complications of pregnancy and trophoblast pathology.

Trophoblastic hormone (TBH)

Determination of the TBG level is used for the diagnosis and monitoring of a number of oncological diseases, primarily trophoblast tumors. Detection of TBG in the blood in cancer of the uterus and ovaries indicates an increased malignancy of the tumor.


C-peptide is a biologically inactive marker of carbohydrate metabolism, an indicator of endogenous insulin secretion.The test is used to diagnose diabetes mellitus and monitor therapy, since the measurement of C-peptide makes it possible to assess insulin secretion even while taking exogenous insulin and in the presence of autoantibodies to insulin.


Measurement of proinsulin concentration is used in the diagnosis of pancreatic beta cell tumors (insulin).

Plasma catecholamines (adrenaline, norepinephrine, dopamine)

The study is used in the diagnosis of pheochromocytomas, differential diagnosis of hypertensive conditions, with dysfunctions of the sympathoadrenal system and pathological conditions associated with changes in serotonin levels.

Plasma histamine (Histamine, plasma)

The test is used in the diagnosis of histamine-producing carcinoid tumors, laboratory confirmation of anaphylactic reactions.

Aldosterone (blood) (Aldosterone)

The main mineralocorticoid hormone of the adrenal cortex, involved in the regulation of sodium and potassium balance, maintaining blood pressure and blood volume.


Leptin is a hormone secreted by fat cells and involved in the regulation of energy metabolism.Determination of the level of leptin in blood serum can be used in a complex examination for problems of increasing or decreasing body weight, in the differential diagnosis of type II diabetes mellitus and obesity, as an indicator of the risk of developing coronary heart disease. Also, the analysis is used to identify the causes of secondary amenorrhea.


Peptide hormone of the gastrointestinal tract. The test is used in the diagnosis of Zollinger-Alison syndrome and the monitoring of gastrin-producing gastrinomas.

Gastrin-17 (stimulated)

The test is carried out in addition to the study “Gastropanel” in the complex diagnosis of dyspeptic disorders, for the early diagnosis of H. pylori-associated chronic gastritis, assessment of the localization, nature and severity of the pathological process, in order to determine the risk of peptic ulcer and cancer stomach (non-invasive examination to select patients in need of gastroscopy followed by biopsy).

Pancreatic hormones

The pancreas is an organ of the digestive system.It performs exocrine (exocrine) and intrasecretory (endocrine) functions. The exocrine function of the pancreas is realized by the secretion of pancreatic juice, which contains enzymes involved in digestion. The intrasecretory function of the pancreas is to produce hormones involved in the regulation of carbohydrate, fat and protein metabolism.

The endocrine part of the pancreas is represented by pancreatic islets, or islets of Langerhans.The islets are composed of cells in which hormones are synthesized.

  • b cells produce insulin
  • a-cells produce glucagon
  • D cells produce somatostatin and gastrin
  • PP cells produce pancreatic polypeptide.

Proinsulin – a protein that is synthesized in the b-cells of the islets of the pancreas. It is almost completely converted to insulin after the C-peptide molecule is cleaved from it.A small fraction of it, which has not turned into insulin, enters the bloodstream unchanged. The biological activity of proinsulin is much lower than that of insulin. Most often, the determination of the level of proinsulin is used in the diagnosis of insulinomas. Insulinoma is a tumor of the b-cells of the islets of Langerhans that secretes insulin uncontrollably.

Insulin is necessary for the transport of glucose – the main source of energy for the cells of our body, as well as potassium and amino acids into the cells.Insulin itself cannot penetrate cells, therefore it performs its function through interaction with receptors on the cell surface. It also stimulates glycolysis and glycogen synthesis in the liver and muscles. Absolute insulin deficiency due to damage to b-cells is the cause of type 1 diabetes mellitus. If the disorder occurs at the stage of interaction of insulin with cells, type 2 diabetes mellitus develops. At the same time, there is enough insulin in the blood, its synthesis is not disturbed, but the cells “do not feel” it.In both cases, the level of glucose in the blood rises, since there is no one to transport it to the cells. This condition is called hyperglycemia. There is also the opposite situation, when there is too much insulin in the blood. This leads to a decrease in blood glucose levels – hypoglycemia. Insulinoma is the most common cause of excess insulin secretion.

C-peptide is derived from proinsulin. It is an indicator of insulin secretion. The half-life of C-peptide from the bloodstream is 30-40 minutes, which is an order of magnitude longer than that of insulin, and its concentration is about 5 times higher than that of insulin.It is useful to determine C-peptide in patients who are observed after removal of the pancreas, for the diagnosis of hypoglycemic conditions, with suspected insulinoma. Also, C-peptide allows you to assess the level of endogenous insulin when taking insulin preparations, or in the presence of antibodies to insulin in the blood.

Glucagon is synthesized by a-cells of the pancreas and is an insulin antagonist. Its increase serves as a signal for the body to increase the level of glucose in the blood.This is achieved by the breakdown of glycogen to glucose molecules, or the formation of glucose in an alternative way (gluconeogenesis).

Gastrin stimulates gastric secretion. Its concentration changes during the day. After a meal, the concentration of gastrin increases by 1.5-2 times. Gastrin synthesis is stimulated by a decrease in the level of hydrochloric acid in the stomach. Determination of the level of gastrin is used in the diagnosis and control of the treatment of Zollinger-Ellison syndrome, or gastrinoma, in which 2/3 of patients have a 10-fold increase in the level of fasting serum gastrin (> 1000 pg / ml).