General Chemical Structure and Function of the Endocrine System of Animals – Endocrine System

Steroid hormones are derivatives of cholesterol and include products of the adrenal cortex, ovaries, and testes as well as the related molecule, vitamin D. Unlike protein/polypeptide hormones, mature steroid hormones are not stored in large amounts. When needed, they are rapidly synthesized from cholesterol by a series of enzymatic reactions. Most of the cholesterol needed for rapid steroid hormone synthesis is stored intracellularly in the tissue of origin. In response to appropriate signals, the precursor is moved to organelles (mitochondria and smooth endoplasmic reticulum), where a series of enzymes (eg, isomerases, dehydrogenases) rapidly convert the molecule to the appropriate steroid hormone. The identity of the final steroidal product is thus dictated by the set of enzymes expressed in that tissue.

Steroid hormones are hydrophobic and pass through cell membranes easily. In blood, they are bound, to a great extent, to carrier proteins. Albumin binds many steroids fairly loosely; in addition, specific binding globulins exist for many steroid hormones. Most of the steroid hormone in circulation is bound to carrier proteins, and a small fraction circulates free or unbound. This latter fraction is thought to be available for target cell entry, ie, the biologically active portion. A rapid equilibrium exists between protein-bound and unbound steroid in extracellular fluid. Possible roles for steroid hormone–binding proteins include aiding in tissue delivery of steroids by providing an even distribution to all cells within a target tissue, buffering against large fluctuations in free hormone, and prolonging the half-life of steroids in blood. Relative to protein/polypeptide hormones, steroids usually have longer half-lives, often in the range of many minutes to hours.

Steroid hormones act on target cells via receptors located in the cell interior. These receptors are generally found in the nucleus, although some appear to reside, when unoccupied, in the cytoplasm. There are several classes of steroid receptors—those for glucocorticoids, mineralocorticoids, progestins, etc. Steroid receptors comprise a family of related proteins that also show homology to receptors for the thyroid hormones and vitamin D. The receptor has regions or domains that carry out specific tasks: one for recognition and binding of the steroid, another for binding to a specific region on chromosomal DNA, and a third for helping regulate the transcriptional complex.

Steroid hormones enter targets by diffusing through the cell membrane and then binding to the receptor, causing a conformational change in the new complex. This, in turn, leads to release of associated proteins (eg, heat-shock proteins) and movement to the nucleus (if necessary), followed by binding of the complex to regions of DNA located near specific steroid-regulated genes. The result is a change in the rate of transcription of specific genes, either increasing or decreasing their expression. Thus, steroid hormones primarily function by affecting the production rates of specific messenger RNA and proteins in targets.

Steroid action is relatively slow in onset (hours) but may be long lasting because of the duration of production and half-lives of the messenger RNA and proteins induced in target cells. It is increasingly clear that some steroids also act via nongenomic mechanisms. For example, many of the anti-inflammatory effects of glucocorticoids are thought to be due to the glucocorticoid-receptor complex binding to, and inhibiting the action of, pro-inflammatory transcription factors inside cells. In addition, rapid effects of steroids are likely mediated at least in part by their binding to non-classic receptors located on target cell membranes.

Steroids in the blood are eliminated by metabolism in the liver. Reduced forms are produced and subsequently conjugated to glucuronic acid and sulfate. These metabolites are freely soluble in blood and are eliminated from the body by renal excretion and through the GI tract. Small amounts of free steroid hormone are also directly excreted by the kidneys.

Structure and Function of the Endocrine System in Dogs

Below is information about the structure and function of the canine endocrine system. We will tell you about the general structure of endocrine system, how it works in dogs, common diseases that affect the endocrine system and common diagnostic tests performed to evaluate the endocrine system in dogs. 

What Is the Endocrine System?

The endocrine system is composed of several different types of glands and organs that produce the hormones of the dog’s body. A hormone is a chemical that is secreted by a gland in one area of the body and is carried by the bloodstream to other organs in the body, where it exerts some effect. Most hormones regulate the activity or structure of their target organs. The overall effect of the endocrine system is to regulate, coordinate and control many different bodily functions. The endocrine system includes the hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands, part of the gastrointestinal tract, pancreas, kidneys, liver, ovaries and testes.

Where Is the Endocrine System Located in Dogs?

The endocrine system is scattered throughout the body as follows:

The ovaries are located in the middle part of the abdominal cavity near the kidneys.

What Is the General Structure of the Canine Endocrine System?

The endocrine system is made up of a collection of glands distributed throughout the body. The endocrine glands produce hormones and secrete them directly into the internal environment where they are transmitted via the bloodstream. Hormones produce certain effects at different points in the body. Some endocrine glands are directly under the control of the pituitary gland. For example, the adrenal gland is controlled by the pituitary hormone, adrenocorticotropic hormone (ACTH). ACTH causes the adrenal glands to produce cortisone (cortisol), which is also a hormone. Other endocrine glands respond directly or indirectly to concentrations of substances in the blood, such as the insulin-secreting cells of the pancreas responding to the sugar concentration in the blood.

What Are the Functions of the Endocrine System in Dogs?

The major function of the endocrine system is to regulate numerous bodily functions, using specific hormones as messengers. Some hormones affect nearly all cells, while others regulate and affect only a single organ. Hormones act by regulating cell metabolism, by changing or maintaining enzyme activity in receptor cells, and by controlling growth and development, metabolic rate, sexual rhythms and reproduction.

The amount of hormone produced at any one time is controlled by feedback mechanisms. These feedback mechanisms are interactions between the endocrine glands, the blood levels of the various hormones, and certain activities of the target organ. For example, when the pituitary gland increases the secretion of ACTH, the increased levels are detected by the adrenal gland, and the end result is more production of cortisone hormone by the adrenal glands. As the cortisol levels rise in the bloodstream, the hypothalamus eventually detects these higher levels and sends a message to the pituitary gland. The pituitary gland then turns down its own production of ACTH. As the ACTH levels in the bloodstream subsequently fall, the adrenal gland decreases its production of cortisol to a normal level again. This is called a negative feedback loop.

What Are Common Diseases of the Endocrine System in Dogs?

Diseases of the endocrine system can arise with either overproduction or underproduction of hormones. There are numerous diseases of the endocrine system in dogs.

The endocrine disorders associated with the pituitary gland fall into two types: under production of hormones (hypofunction of the gland), and excessive production of hormones (hyperfunction of the gland).

Undersecretion of pituitary growth hormone (GH) is not very common in the dog, but can occur in both puppies and adult dogs. Insufficient production of growth hormone in puppies results in dwarfism. When the production of GH is abnormally low in the adult dog, hair loss is the major symptom.

Overproduction of growth hormone causes a disorder called acromegaly. Acromegaly in the dog usually develops as a side effect to the long-term administration of progesterone drugs, but can also develop from a pituitary tumor. Affected dogs develop blunt and broad faces with excessive skin folds on the face and neck. They may develop enlargement of the abdomen, lethargy, weight gain and neurologic signs.

What Types of Diagnostic Tests Are Used to Evaluate the Endocrine System?

There are several tests that are helpful in evaluating the endocrine system.

In addition, blood tests have been developed that measure the response of endocrine glands to stimulating hormones. Most of these stimulating tests are timed blood tests. An initial blood sample is taken and the resting level of hormone is measured in that sample. Then a substance is injected into the body, and at some later time (usually within several hours), a second blood sample is taken. The hormone assay is repeated in the second sample to see if the hormone level has changed. Some stimulating tests involve giving different substances in sequence, with several blood samples taken at different intervals. The adrenal glands and thyroid glands are the most common endocrine glands evaluated by using stimulation tests.

CT scans and MRIs are very useful in evaluating the endocrine glands. They can often detect enlargement of the glands, distortion in their shape, and changes in their location and size. They provide valuable information about the structure of the glands, but they do not give much information on the function of the glands.

Some endocrine diseases are easy to diagnose, while others can be very difficult to confirm. Some endocrine disorders are not diagnosed until multiple tests are performed, sometimes over a period of time.

What is the Endocrine System?

21.1: What is the Endocrine System?

The endocrine system sends hormones—chemical signals—through the bloodstream to target cells—the cells the hormones selectively affect. These signals are produced in endocrine cells, secreted into the extracellular fluid, and then diffuse into the blood. Eventually, they diffuse out of the blood and bind to target cells which have specialized receptors to recognize the hormones.

Alternate Routes

While most hormones travel through the circulatory system to reach their target cells, there are also alternate routes to bring hormones to target cells. Paracrine signaling sends hormones out of the endocrine cell and into the extracellular fluid where they affect local cells. In a form of paracrine signaling, called autocrine signaling, hormones secreted into the extracellular fluid affect the cell that secreted them.

Another type of signaling, synaptic signaling, involves the release of neurotransmitters from neuron terminals into the synapse—a specialized junction that relays information between neurons—where they bind to receptors on neighboring neurons, muscle cells, and glands. In neuroendocrine signaling, neurosecretory cells secrete neurohormones that travel through the blood to affect target cells. Overall, endocrine signaling has a slower effect than other types of signaling because it takes longer for hormones to reach the target cells, but the effects typically also last longer.

Hormone Release

Hormones directly diffuse into the extracellular fluid surrounding the endocrine glands because they have no ducts. In comparison, exocrine glands, like the salivary gland, have ducts that secrete a targeted dose directly onto a surface or into a cavity. In addition to being found in specialized endocrine glands, endocrine cells can also be located in organs like the stomach, among cells with different functions.

Target Cells

A hormone has specific target cells that have receptors that recognize the hormone. It can be thought of like a lock and key where the receptors on a target cell are the lock and will only recognize the hormone, the key, that fits it. Target cells can be very close to the endocrine cells that produce the hormone or very far away but must be transported through the bloodstream. For instance, enteroendocrine cells in the stomach and small intestine release hormones that can alter gastric acid secretion by stomach cells. On the other hand, hormones released by the pituitary gland located at the base of the brain can affect urine production by acting on kidney cells.

Suggested Reading

Jones, Christopher M., and Kristien Boelaert. “The Endocrinology of Ageing: A Mini-Review.” Gerontology 61, no. 4 (2015): 291–300. [Source]

Yang, Oneyeol, Hye Lim Kim, Jong-Il Weon, and Young Rok Seo. “Endocrine-Disrupting Chemicals: Review of Toxicological Mechanisms Using Molecular Pathway Analysis.” Journal of Cancer Prevention 20, no. 1 (March 2015): 12–24. [Source]

15.2: An Overview of the Endocrine System

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

• Distinguish the types of intercellular communication and their importance
• Identify the major organs and tissues of the endocrine system and their location in the body
• Explain the role of hormones in controlling body functions via the bloodstream
• Discuss the role of feedback loops in hormone control

Communication is a process in which a sender transmits signals to one or more receivers to control and coordinate actions. In the human body, two major organ systems participate in relatively “long distance” communication: the nervous system and the endocrine system. Together, these two systems are primarily responsible for maintaining homeostasis in the body.

Neural and Endocrine Signaling

The nervous system uses two types of intercellular communication—electrical and chemical signaling—either by the direct action of an electrical potential, or in the latter case, through the action of chemical neurotransmitters such as serotonin or norepinephrine. In a synapse, neurotransmitters act locally and rapidly. When an electrical signal in the form of an action potential arrives at the synaptic terminal, neurotransmitters diffuse across the synaptic cleft (the gap between a sending neuron and a receiving cell). Once the neurotransmitters interact (bind) with receptors on the receiving (post-synaptic) cell, the receptor stimulation is transduced into a response such as continued electrical signaling or modification of cellular response. The target cell responds within milliseconds of receiving the chemical “message”; this response then ceases very quickly once the neural signaling ends. In this way, neural communication enables body functions that involve quick, brief actions, such as movement, sensation, and cognition.

In contrast, the endocrine system uses just one method of communication: chemical signaling. These signals are sent by the endocrine organs, which secrete chemicals—the hormone—into the extracellular fluid. Hormones are transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, inducing a characteristic response. As a result, endocrine signaling requires more time than neural signaling to prompt a response in target cells, though the precise amount of time varies with different hormones. For example, the hormones released when you are confronted with a dangerous or frightening situation, called the fight-or-flight response, occur by the release of adrenal hormones—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 signaling. The same hormone may play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone oxytocin promotes uterine contractions in women during labor. It is also important in breastfeeding, and may be involved in the sexual response and in feelings of emotional attachment in both males and females.

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 (Table \(\PageIndex{1}\)). 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. 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.

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 these ductless glands is to secrete their hormones directly into the surrounding fluid. The 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 (summarized in Figure \(\PageIndex{1}\) and covered in more detail in subsequent sections of this chapter). Some 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 hormones 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, adipose tissue has long been known to produce hormones, and recent research has revealed that even bone tissue has endocrine functions.

Figure \(\PageIndex{1}\): Endocrine System. Endocrine glands and cells are located throughout the body and play an important role in homeostasis. The pineal gland is posterior to the thalamus in the brain, while the pituitary gland is connected to the inferior hypothalamus by way of the infundibulum. The bilobed thyroid gland is between the thyroid cartilage of the larynx and the trachea, with two pairs of parathyroid glands bilateral on its posterior surface. The adrenal glands lie on the superior surface of the kidneys while the pancreas runs across the midline anterior to the kidneys, inferoposterior to the stomach. The gonads include the ovaries bilateral to the uterus in the female and the testes bilateral in the scrotum in the male. (Image credit: “The Endocrine System” by OpenStax is licensed under CC BY 3.0)

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 (inside) of the small intestine.

Other Types of Chemical Signaling

In endocrine signaling, hormones secreted into the extracellular fluid diffuse into the blood or lymph (fluid of the lymphatic system), and can then travel great distances throughout the body. In contrast, autocrine signaling takes place within the same cell. An autocrine (auto- = “self”) is a chemical that elicits a response in the same cell that secreted it. Interleukin-1, or IL-1, is a signaling molecule that plays an important role in the inflammatory response. The cells that secrete IL-1 have receptors on their cell surface that bind these molecules, resulting in autocrine signaling.

Local intercellular communication is carried out by a paracrine, also called a paracrine factor, which is a chemical that induces a response in neighboring cells within the same tissue. Although paracrine hormones may enter the bloodstream, their concentration is generally too low to elicit a response from distant tissues. Histamine, released by immune cells of the bronchial tree, is a familiar example of a paracrine that is harmful to people with asthma. Histamine causes the walls of the bronchi to become inflamed and causes the smooth muscle cells of the bronchi to constrict, narrowing the airways. Neurotransmitters of the nervous system, acting locally within the synaptic cleft, are another example of paracrine signaling.

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 \(\PageIndex{2}\).

Types of Hormones

The hormones of the human body can be divided into two major groups on the basis of their chemical properties: hormones that are soluble in water, most of which are derived from amino acids (the building blocks of proteins), and steroid hormones, which are not soluble in water as they are derived from the lipid cholesterol. The chemical properties of the hormones in each group affect much of how they work including how they are distributed to target cells, the type of receptors they bind to, and other aspects of function such as how long effects can last.

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.

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. Glucocorticoids such as cortisol help the body respond to stress. If glucocorticoid concentrations in the blood fall below optimal, as measured by sensors in the bloodstream, the hypothalamus releases corticotropin-releasing hormone (CRH). The release of CRH signals the pituitary gland to initiate a cascade of hormone releases that ultimately signal the adrenal gland (aka suprarenal gland) to release glucocorticoids into the bloodstream. As glucocorticoid concentrations in the blood rise, the hypothalamus and pituitary gland reduce their signaling to the adrenal glands to prevent additional glucocorticoid secretion (Figure \(\PageIndex{2}\)).

Figure \(\PageIndex{2}\): Negative Feedback Loop. The hypothalamus perceives low blood concentrations of glucocorticoids via sensors in the blood vessels. The imbalance triggers the hypothalamus to release corticotropin-releasing hormone (CRH) via the anterior pituitary. CRH releases starts a hormone cascade that triggers the adrenal glands to release glucocorticoids into the blood, increasing blood levels of glucocorticoids. Glucocorticoids such as cortisol regulate the body’s stress responses. When the hypothalamus perceives normal blood concentrations of glucocorticoids, it stops releasing CRH, so this is an example of a negative-feedback loop. (Image credit: “Negative Feedback Loop” by OpenStax is licensed under CC BY 3.0)

Role of Endocrine Gland Stimuli

Reflexes triggered by both chemical and neural stimuli control endocrine activity. These reflexes may be simple, involving only one hormone response, or they may be more complex and involve many hormones, as is the case with the hypothalamic control of various anterior pituitary–controlled hormones.

Humoral stimuli are changes in blood levels of nutrients, ions, or other non-hormonal chemicals that cause the release or inhibition of a hormone to maintain homeostasis. For example, osmoreceptors in the hypothalamus detect changes in blood osmolarity (the concentration of solutes in the blood plasma). If blood osmolarity is too high, meaning that the blood is not dilute enough, osmoreceptors signal the hypothalamus to release ADH. The hormone causes the kidneys to reabsorb more water and reduce the volume of urine produced. This reabsorption causes a reduction of the osmolarity of the blood, diluting the blood to the appropriate level. The regulation of blood glucose is another example. High blood glucose levels cause the release of insulin from the pancreas, which increases glucose uptake by cells and liver storage of glucose as glycogen.

An endocrine gland may also secrete a hormone in response to the presence of another hormone produced by a different endocrine gland. Such hormonal stimuli often involve the hypothalamus, which produces releasing and inhibiting hormones that control the secretion of a variety of pituitary hormones.

In addition to these chemical signals, hormones can also be released in response to neural stimuli. A common example of neural stimuli is the activation of the fight-or-flight response by the sympathetic nervous system. When an individual perceives danger, sympathetic neurons signal the adrenal glands to secrete norepinephrine and epinephrine. The two hormones dilate blood vessels, increase the heart and respiratory rate, and suppress the digestive and immune systems. These responses boost the body’s transport of oxygen to the brain and muscles, thereby improving the body’s ability to fight or flee.

EVERYDAY CONNECTIONS

Bisphenol A and Endocrine Disruption

You may have heard news reports about the effects of a chemical called bisphenol A (BPA) in various types of food packaging. BPA is used in the manufacturing of hard plastics and epoxy resins. Common food-related items that may contain BPA include the lining of aluminum cans, plastic food-storage containers, drinking cups, as well as baby bottles and “sippy” cups. Other uses of BPA include medical equipment, dental fillings, and the lining of water pipes.

Research suggests that BPA is an endocrine disruptor, meaning that it negatively interferes with the endocrine system, particularly during the prenatal and postnatal development period. In particular, BPA mimics the hormonal effects of estrogens and has the opposite effect—that of androgens. The U. S. Food and Drug Administration (FDA) notes in their statement about BPA safety that although traditional toxicology studies have supported the safety of low levels of exposure to BPA, recent studies using novel approaches to test for subtle effects have led to some concern about the potential effects of BPA on the brain, behavior, and prostate gland in fetuses, infants, and young children. The FDA is currently facilitating decreased use of BPA in food-related materials. Many US companies have voluntarily removed BPA from baby bottles, “sippy” cups, and the linings of infant formula cans, and most plastic reusable water bottles sold today boast that they are “BPA free.” In contrast, both Canada and the European Union have completely banned the use of BPA in baby products.

The potential harmful effects of BPA have been studied in both animal models and humans and include a large variety of health effects, such as developmental delay and disease. For example, prenatal exposure to BPA during the first trimester of human pregnancy may be associated with wheezing and aggressive behavior during childhood. Adults exposed to high levels of BPA may experience altered thyroid signaling and male sexual dysfunction. BPA exposure during the prenatal or postnatal period of development in animal models has been observed to cause neurological delays, changes in brain structure and function, sexual dysfunction, asthma, and increased risk for multiple cancers. In vitro studies have also shown that BPA exposure causes molecular changes that initiate the development of cancers of the breast, prostate, and brain. Although these studies have implicated BPA in numerous ill health effects, some experts caution that some of these studies may be flawed and that more research needs to be done. In the meantime, the FDA recommends that consumers take precautions to limit their exposure to BPA. In addition to purchasing foods in packaging free of BPA, consumers should avoid carrying or storing foods or liquids in bottles with the recycling code 3 or 7. Foods and liquids should not be microwave-heated in any form of plastic: use paper, glass, or ceramics instead.

CAREER CONNECTIONS

Endocrinologist

Endocrinology is a specialty 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 mellitus. Endocrine surgeons treat endocrine disease through the removal, or resection, of the affected endocrine gland.

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.

Concept Review

The endocrine system consists of cells, tissues, and organs that secrete hormones critical to homeostasis. 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 into the extracellular fluid. From there, hormones diffuse into the bloodstream and may travel to distant body regions, 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 hormone-secreting cells.

Hormones are released upon stimulation that is of either chemical or neural origin. Regulation of hormone release is primarily achieved through negative feedback. Various stimuli may cause the release of hormones, but there are three major types. Humoral stimuli are changes in ion or nutrient levels in the blood. Hormonal stimuli are changes in hormone levels that initiate or inhibit the secretion of another hormone. Finally, a neural stimulus occurs when a nerve impulse prompts the secretion or inhibition of a hormone.

Review Questions

Q. Endocrine glands ________.

A. secrete hormones that travel through a duct to the target organs

B. release neurotransmitters into the synaptic cleft

C. secrete chemical messengers that travel in the bloodstream

D. include sebaceous glands and sweat glands

Answer

Answer: C

Q. Chemical signaling that affects neighboring cells is called ________.

A. autocrine

B. paracrine

C. endocrine

D. neuron

Answer

Answer: B

Q. A student is in a car accident, and although not hurt, immediately experiences pupil dilation, increased heart rate, and rapid breathing. What type of endocrine system stimulus did the student receive?

A. humoral

B. hormonal

C. neural

D. positive feedback

Answer

Answer: C

Critical Thinking Questions

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

Answer

A. 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.

Q. Compare and contrast endocrine and exocrine glands.

Answer

A. 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.

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

Answer

A. 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.

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

hormonal stimuli

the presence of a hormone causes the release or inhibition of another hormone in an endocrine gland

hormone receptor

protein within a cell or on the cell membrane that binds a hormone, initiating the target cell response

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

humoral stimuli

changes in blood levels of non-hormone chemicals such as ions or nutrients that cause release or inhibition of a hormone to maintain homeostasis of the chemical

negative feedback loop

type of regulation in which increasing levels of a substance signal that the substance no longer needs to be released, resulting in lowered levels of the substance

neural stimuli

a nerve impulse causes the release or inhibition of a hormone in an endocrine gland

paracrine

chemical signal that elicits a response in neighboring cells; also called paracrine factor

Contributors and Attributions

An Overview of the Endocrine System – Anatomy & Physiology

OpenStaxCollege

Learning Objectives

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

• Distinguish the types of intercellular communication, their importance, mechanisms, and effects
• Identify the major organs and tissues of the endocrine system and their location in the body

Communication is a process in which a sender transmits signals to one or more receivers to control and coordinate actions. In the human body, two major organ systems participate in relatively “long distance” communication: the nervous system and the endocrine system. Together, these two systems are primarily responsible for maintaining homeostasis in the body.

The nervous system uses two types of intercellular communication—electrical and chemical signaling—either by the direct action of an electrical potential, or in the latter case, through the action of chemical neurotransmitters such as serotonin or norepinephrine. Neurotransmitters act locally and rapidly. When an electrical signal in the form of an action potential arrives at the synaptic terminal, they diffuse across the synaptic cleft (the gap between a sending neuron and a receiving neuron or muscle cell). Once the neurotransmitters interact (bind) with receptors on the receiving (post-synaptic) cell, the receptor stimulation is transduced into a response such as continued electrical signaling or modification of cellular response. The target cell responds within milliseconds of receiving the chemical “message”; this response then ceases very quickly once the neural signaling ends. In this way, neural communication enables body functions that involve quick, brief actions, such as movement, sensation, and cognition.In contrast, the endocrine system uses just one method of communication: chemical signaling. These signals are sent by the endocrine organs, which secrete chemicals—the hormone—into the extracellular fluid. Hormones are transported primarily via the bloodstream throughout the body, where they bind to receptors on target cells, inducing a characteristic response. As a result, endocrine signaling requires more time than neural signaling to prompt a response in target cells, though the precise amount of time varies with different hormones. For example, the hormones released when you are confronted with a dangerous or frightening situation, called the fight-or-flight response, occur by the release of adrenal hormones—epinephrine and norepinephrine—within seconds. In contrast, it may take up to 48 hours for target cells to respond to certain reproductive hormones.

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 addition, endocrine signaling is typically less specific than neural signaling. The same hormone may play a role in a variety of different physiological processes depending on the target cells involved. For example, the hormone oxytocin promotes uterine contractions in women in labor. It is also important in breastfeeding, and may be involved in the sexual response and in feelings of emotional attachment in both males and females.

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 ([link]). 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. 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.

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 these ductless glands is to secrete their hormones directly into the surrounding fluid. The 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 ([link]). 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 hormones 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, adipose tissue has long been known to produce hormones, and recent research has revealed that even bone tissue has endocrine functions.

Endocrine System

Endocrine glands and cells are located throughout the body and play an important role in homeostasis.

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.

In endocrine signaling, hormones secreted into the extracellular fluid diffuse into the blood or lymph, and can then travel great distances throughout the body. In contrast, autocrine signaling takes place within the same cell. An autocrine (auto- = “self”) is a chemical that elicits a response in the same cell that secreted it. Interleukin-1, or IL-1, is a signaling molecule that plays an important role in inflammatory response. The cells that secrete IL-1 have receptors on their cell surface that bind these molecules, resulting in autocrine signaling.

Local intercellular communication is the province of the paracrine, also called a paracrine factor, which is a chemical that induces a response in neighboring cells. Although paracrines may enter the bloodstream, their concentration is generally too low to elicit a response from distant tissues. A familiar example to those with asthma is histamine, a paracrine that is released by immune cells in the bronchial tree. Histamine causes the smooth muscle cells of the bronchi to constrict, narrowing the airways. Another example is the neurotransmitters of the nervous system, which act only locally within the synaptic cleft.

Career Connections

Endocrinologist
Endocrinology is a specialty 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 mellitus. Endocrine surgeons treat endocrine disease through the removal, or resection, of the affected endocrine gland.

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.

The endocrine system consists of cells, tissues, and organs that secrete hormones critical to homeostasis. 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 into the extracellular fluid. From there, hormones diffuse into the bloodstream and may travel to distant body regions, 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 hormone-secreting cells.

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?

Endocrine glands ________.

1. secrete hormones that travel through a duct to the target organs
2. release neurotransmitters into the synaptic cleft
3. secrete chemical messengers that travel in the bloodstream
4. include sebaceous glands and sweat glands

Chemical signaling that affects neighboring cells is called ________.

1. autocrine
2. paracrine
3. endocrine
4. neuron

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

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.

Compare and contrast endocrine and exocrine glands.

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.

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

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.

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

Lab Content

Introduction

The term “endocrine” implies secretion into the internal milieu of a multicellular organism. In contrast to exocrine tissues, where the secretory products are discharged into the external space – the outer surface of the body, mucosal surfaces, duct systems – the endocrine organs and cells secrete their products into the vascular system. The blood vessels then serve as conduits for these secretions to travel to their target tissues.

Endocrine tissues function according to a basic model. Individual cell types respond, via surface receptors, to different signals. They produce a very limited spectrum of secretory products, called hormones, that themselves function as signaling molecules for specific cell populations. These hormones are effective at exceedingly low concentrations. Because of this, relatively few cells are sufficient for the integrative function of large, multicellular organisms. Therefore, endocrine tissues are characteristically present in small quantities.

Pituitary Gland

The pituitary gland, or hypophysis, is a collection of different cell types that control the activity of other endocrine organs. It is governed by the hypothalamus, which sends both electrical and hormonal signals to the pituitary, and by feedback regulation (both positive and negative) through the secretions of its target glands. This slide shows a section of the human pituitary. In the anterior pituitary (pars distalis), you can see cords of cuboidal cells with a wide range of nuclear to cytoplasmic volume ratios. The posterior pituitary (pars nervosa) is connected to the hypothalamus by the pituitary stalk – this is easily visualized because the nervous tissue appears continuous between the two glands.

Anterior Pituitary

The anterior pituitary contains cells that, when viewed under the light microscope, appear as acidophils, basophils, or chromophobes. This slide displays the three cell types of the anterior pituitary under H&E stain. The acidophils appear as cells with pink cytoplasm and dark nuclei. These cells secrete protein hormones like growth hormone and prolactin. The basophils appear as darker cells with purple cytoplasm. These cells secrete glycoprotein hormones such as adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), and leutenizing hormone (LH). Finally, a few chromophobes are visible in this section; these cells are non-secretory and serve as support cells or precursors to the acidophils and basophils.

Posterior Pituitary

The posterior pituitary is mostly composed of unmyelinated axonal processes and terminals of the supraoptic and paraventricular nuclei of the hypothalamus. The pituitary stalk connects the two glands. The posterior pituitary has characteristic Herring bodies, focal axonal swellings that are packed with secretory granules. Pituicytes are the glial cells of the pituitary gland; the nuclei that are visible in sections of posterior pituitary belong to these cells, as well as cells of the vasculature. A third section of the pituitary, the intermediate lobe, is vestigial in man.

Adrenal Gland

The adrenal gland has two distinct parts, the cortex and medulla, which differ in structure and function. The cortex secretes hormones produced from cholesterol and can be functionally and histologically divided into three zones: glomerulosa, fasciculata, and reticularis. The adrenal medulla is the innermost portion of the gland and shares an embryological origin with the sympathetic nervous system.

The zona glomerulosa is the thin outer layer of the adrenal cortex. Its cells are pale staining and organized in ovoid clusters that are separated by capillaries. The cells of the zona glomerulosa produce mineralocorticoid hormones like aldosterone, which regulates salt and water balance.

The zona fasciculata comprises the thick middle layer of the cortex. Its cells are extensively vacuolated because of the presence of lipid droplets. The cells of this region produce glucocorticoids like cortisol, which has metabolic effects.

The zona reticularis is the innermost layer of the adrenal cortex. The border between it and the zona fasciculata is less distinct than that between the previous two zones. Cells in the zona reticularis stain deeply and are less vacuolated. This region produces androgens, which supplement sex hormones produced by the gonads.

The medulla primarily secretes catecholamines, including adrenaline and noradrenaline. Its cells possess abundant cytoplasmic granules that contain stored peptide hormones and catecholamines. These cells are frequently called chromaffin cells because they can be stained with chromium salts. Preganglionic sympathetic fibers traverse the adrenal cortex and synapse directly on chromaffin cells, where they release acetylcholine to stimulate the exocytosis of catecholamine granules during a sympathetic response.

Thyroid

The thyroid is located in the neck and stores large amounts of inactive hormone within extracellular compartments. The thyroid consists of structural units called follicles, which are composed of secretory epithelial cells called principal cells that are adjoined by junctional complexes and surrounded by a basement membrane. Follicles vary in size, but each displays a central lumen containing colloid. Colloid consists of the glycoprotein thyroglobulin, which is secreted by the principal cells and serves as a precursor to thyroid hormone. The height of the principal cells varies according to their level of secretory activity; in hypothyroidism, the cells are squamous or cuboidal, whereas in hyperthyroidism, they are columnar.

Also visible in this slide are a few C-cells, or parafollicular cells, scattered in the spaces between follicles. C-cells secrete calcitonin, which serves as a fine control for calcium homeostasis.

Parathyroid

The parathyroid glands are closely associated with the thyroid. They consist of closely packed groups of two cell types:

• Chief (principal) cells, which have prominent central nuclei surrounded by pale cytoplasm. Chief cells produce parathyroid hormone (PTH), which is the most important regulator of calcium metabolism in humans.
• Oxyphilic cells, which are large and fewer in number, have small, dark nuclei and an acidophilic cytoplasm with many mitochondria. The function of these cells is unknown, but they increase in abundance as a person ages.

Endocrine Pancreas

The endocrine portion of the pancreas is comprised of the islets of Langerhans. During development, the cells of the islets migrate away from the duct system and aggregate around capillaries. The islets contain three important cell types:

• Alpha cells produce glucagon, which increases the plasma glucose concentration. They are primarily located around the periphery of the islets.
• Beta cells produce insulin, which decreases plasma glucose by promoting uptake by liver, skeletal muscle, and adipose tissue. Beta cells are typically located in the center of the islets.
• D-cells produce somatostain, which has broad effects on gastrointestinal function and inhibits insulin and glucagon secretion. Delta cells are scattered throughout the islets.

Endocrine System Physiology Lab Activity

We are pleased to announce the release of our Endocrine Physiology Lab, an interactive lab covering the basic structure and function of the endocrine system as well as the importance of feedback loops in regard to endocrine communication.

Students work together to identify the major endocrine organs and examine how different hormones contribute to homeostasis using three unique experiments involving virtual rat activities and feedback loop scenarios.

The lab is part of our suite of  30+ lessons and labs that make up our Lt Human Physiology collection, an online teaching solution suitable for both remote and in-person learning. 

Take a quick tour through the endocrine lab activities in the video below, and find out what you and your students can expect from this exciting new lesson!

What is endocrine physiology?

Simply said, endocrine physiology describes the system in our bodies that uses hormones to initiate and control body functions such as: reproduction, growth, development, metabolism, and stress. In humans and animals, the endocrine system is a combination of feed-forward and feedback loops, resulting in the secretion of specific hormones directly into the bloodstream, from where they affect almost every cell in our bodies.

Why is it so difficult to teach?

The endocrine system is a rather complex body system composed of multiple interweaved pathways. Because of this complexity, it is often ignored or reduced to just the reproductive system in undergraduate education. When taught, it is often only taught in lecture format as it is difficult and expensive to perform in-lab activities since hormones are hard to measure.

Would you dare to perform an enzyme-linked immunosorbent assay (ELISA) with your class?

Introducing the Endocrine Physiology Lab 

Our interactive Endocrine Physiology Lab is now part of Lt’s Human Physiology collection, a complete curriculum of ready-to-use lessons and labs for teaching undergraduate physiology. 

You can perform this lab with your students in the classroom, or your students can complete the lab at home as the engaging activities do not require access to a lab.  

What’s in the lab? 

Overview of endocrine system structure and function

The lab reviews the location of endocrine organs in our body and the specific hormones the brain uses to interact with these organs.

The focus of the lab is on three endocrine systems: the stress axis (HPA), reproductive axis (HPG), and the metabolic axis (HPT), and utilizes these to explain the basic functionality of the endocrine system. Furthermore, the lab introduces the concept of homeostasis and hormone profiles, and how these might get disturbed when the endocrine system malfunctions. 

The Endocrine Physiology Lab includes interactive diagrams demonstrating how different hormones within a feedback loop can influence each other. 

The lab has been thoughtfully designed, breaking down complex endocrine concepts into easy-to-understand principles, using interactive real-life example scenarios and case study data activities targeted at 1st and 2nd-year undergraduate students.
 

Hormone feedback loop activities

The recurring principle that spans through the entire lab is the importance of feedback loops in regard to endocrine communication. Students first encounter this with real-life scenarios where they identify if the stress response, childbirth, and pupil constriction are negative feedback loops. Afterward, an interactive activity encourages students to use their critical thinking skills to identify a hormone that was repetitively administered to a “virtual” rat by analyzing the changes this manipulation caused to the animal’s organ weights. Students are then guided through a series of questions that help them explain their findings and consolidate their knowledge about the specific endocrine system. 

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  The lab includes a range of interactive question types including drag and drop diagrams.

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  Students work through different scenarios to improve their understanding of homeostasis.

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  Virtual rat activities are used to test student’s understanding of hormone feedback pathways.

Review & Intergration

The lab closes with a review and integration page that encourages students to summarize their learnings by creating an overview diagram of the endocrine system, including all endocrine organs and the respective hormones. Furthermore, students are challenged to compare the endocrine system with the nervous system and highlight the main differences. Finally, reflective questions are asked to encourage students’ curiosity about the endocrine system and build metacognition. 

How can I access the Lab?

For those already using Lt, you can import the Endocrine Lab as part of the Human Physiology collection.

New to Lt? No worries! You can preview the lab for free using the preview button below.  Or, for those wanting to get stuck in and start using the lab immediately, you can sign up for our 90-day free trial!

Additional resources:

Teach them a lesson they’ll never forget! The Muscle Twitch Response experiment »

Understand Your Physiology: Active online-learning resource for physiology students »

How to teach anatomy remotely »

10 Tips for Teaching Online – How to successfully teach remotely and keep your students engaged »

Are you interested in using Lt to deliver your course? Try Lt now – for free!

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Laboratory for the development of the endocrine system

Yaglova Natalya Valentinovna

Doctor of Medical Sciences, specialties 03. 03.04 – cell biology, cytology, histology; 03.01.04 – biochemistry

Head of the laboratory for the development of the endocrine system

Leading specialist in the field of histophysiology and biochemistry of the endocrine system, author of more than 200 scientific works, including 3 monographs, 2 textbooks for universities, 5 textbooks, author of 3 scientific discoveries and 2 patents for inventions.

Tel .: (499) 120-04-79

E-mail: [email protected] [email protected]

N.V. Yaglova, after graduating from the Peoples’ Friendship University of Russia, entered graduate school and worked as a teacher and research assistant at the Department of Biochemistry at the RUDN University. In 2005. She defended her Ph.D. thesis on the topic: “Creation of a sterically stabilized immunoliposomal system based on monoclonal antibodies for the purpose of specific delivery of biologically active substances to target cells”, carried out under the leadership of Academician T. T. Berezov and Academician V.P. Chekhonin, specialty 03.01.04 – biochemistry. In 2006. moved to work at the Research Institute of Human Morphology as a senior researcher. In 2011. defended her doctoral dissertation “Morphological and biochemical study of the secretory activity of the thyroid gland in the experimental syndrome of non-thyroid diseases” in the specialties: 03.03.04 – cell biology, cytology, histology; 03.01.04 – biochemistry.

In 2012 N.V. Yaglova headed the laboratory for the development of the endocrine system.Under her supervision, 2 candidate and 1 doctoral dissertations were defended. Along with the scientific activity of N.V. Yaglova is engaged in scientific and pedagogical activities: training highly qualified personnel, is the author of the basic educational programs of postgraduate professional education (postgraduate studies) in the specialties 03.03.04 – cell biology, cytology, histology; 03.03.05 – developmental biology, embryology, one of the developers of the method of individual developmental education and the co-author of 5 approved textbooks and 2 textbooks for the programmed study of the basic content of cytology, embryology and histology for universities.

N.V. Yaglova is actively involved in scientific and social activities. She was the chairman of the Council of Young Scientists of the Research Institute of Human Morphology, a member of the Dissertation Council D 001.004.01 at the Research Institute of Human Morphology, a member of the editorial board of the journal Clinical and Experimental Morphology, a member of the organizing committee of international scientific conferences.

History of the laboratory for the development of the endocrine system

The laboratory was founded in January 2008.Academician of MAAO, Doctor of Medical Sciences, was elected as its head. Professor V.V. Yaglov is a leading specialist in the study of morphology, histophysiology and pathology of the endocrine glands. Since 2012 the laboratory is headed by Dr. med. N.V. Yaglova.

Laboratory staff:

Yaglova Natalia Valentinovna, MD (03.03.04 – cell biology, cytology, histology; 03. 01.04 – biochemistry) head of the laboratory, e-mail: [email protected]

Yaglov Valentin Vasilievich, Ph.M.Sc. (03.03.04 – cell biology, cytology, histology), Professor, Chief Researcher, [email protected]

Obernikhin Sergei Stanislavovich, MD. (03.03.04 – cell biology, cytology, histology) Senior Researcher, e-mail: [email protected]

Nazimova Svetlana Vladimirovna, Ph.D. (03.01.04 – biochemistry), senior researcher, e-mail: [email protected]

Timokhina Ekaterina Petrovna, Ph.D. (03.03.04 – cell biology, cytology, histology), researcher, e-mail: rodich @ mail.ru

Tsomartova Dibakhan Aslanbekovna, MD (03.03.04 – cell biology, cytology, histology) junior researcher, e-mail: [email protected]

Main scientific directions of the laboratory for the development of the endocrine system:

Endocrine disruptors – new scientific direction in endocrinology. Endocrine disruptors are chemicals of anthropogenic origin that disrupt any stages of the synthesis and interaction of hormones with target cells, which causes changes in the regulation of homeostasis of the human and animal body. For the first time in Russia, comprehensive studies have been carried out and the mechanisms and manifestations of the action of the most common disruptor DDT on the functioning of the thyroid gland, adrenal glands, and organs of the immune system have been established.

Non-thyroid Disease Syndrome (NTHS): The researchers carried out an experimental fundamental study of a new, little-studied syndrome that significantly aggravates the course of many somatic diseases. The pathogenetic mechanisms of SNTZ development, morphological and biochemical manifestations of changes in the secretory cycle of thyroid epithelial cells have been established, and pathogenetically substantiated methods of SNTZ correction have been developed.

Biology and pathology of the diffuse endocrine system: summarized modern ideas about the structural and functional organization of the diffuse endocrine system. A fundamentally important conclusion was made that it develops from the embryonic rudiments of endoderm, ectoderm and mesoderm. Based on this, a conclusion was made about the need to revise the histogenetic classification of tumors of the diffuse endocrine system.

Disorders of the development and functioning of the endocrine and immune systems of the offspring after activation of the immune system of the maternal organism and methods of their correction and prevention is devoted to one of the priority health problems – the protection of the health of mothers and children.It was found that increased proliferation and secretion of cytokines by lymphocytes in the early stages of pregnancy before the formation of the rudiments of the lymphoid organs of the embryo causes disturbances in the postnatal development of the organs of the immune system of the offspring in the prepubertal and postpubertal periods, reduces the reactivity of the immune system.

Structural support of secretory processes is devoted to the study of secretion as a universal biological process that ensures the functioning of a living organism. A method of molecular secretion in adrenal chromaffinocytes and mast cells has been described, ultrastructural mechanisms of changes in the functional activity of corticosterocytes have been established, and regional patterns of secretion in the thyroid gland have been identified and described.

Transcriptional regulation of postnatal morphogenesis of endocrine glands is a recently emerging direction in morphology aimed at identifying factors that regulate the processes of proliferation, differentiation and apoptosis in the development and physiological regeneration of glands.

Histophysiology of the endocrine and immune systems with changes in the content of stable isotopes of biogenic atoms in the body – a new direction of the laboratory’s work, dedicated to the least studied problem of biology and medicine – the role of the balance of isotopes of hydrogen, oxygen, carbon.

Pedagogical activities of the laboratory staff – V. V. Yaglov and N.V. Yaglova developed original methods for obtaining high-quality knowledge in general and private histology, cytology and embryology and objective control of the processes of formation, survival and restoration of knowledge in the course of training specialists, on the basis of which textbooks and textbooks were published, which were highly appreciated by the pedagogical community.

The laboratory for the development of the endocrine system performs complex morphological (histological, histochemical, immunohistochemical, electron microscopic, cytofluorimetric), cultural and biochemical studies in vitro and in vivo.

At the present time, the laboratory staff carry out a state task, carry out work on grants and economic contracts.

Scientific discoveries of laboratory staff:

• Development of inherited transient alopecia areata in mice offspring at the age of 17 days and impaired prenatal and postnatal morphogenesis of mouse skin as a result of increased proliferation and secretion of cytokines by maternal lymphocytes in early pregnancy.
• Ability of rat adrenal chromaffin cells to express the PRH / Hhex transcription factor at different periods of postnatal development and the relationship between a decrease in the proliferative activity of chromaffin cells and activation of PRH / Hhex expression in them in the postnatal period of ontogenesis.
• Ability of corticosterocytes in the glomerular zone of the adrenal cortex of rats to express the Oct4 transcription factor at different periods of postnatal development and the presence of a direct relationship between the number of Oct4-expressing corticosterocytes and the intensity of proliferative processes, as well as an inverse relationship between the functional activity of the glomerular zone and the content of Oct4-positive cells in it …

Defended dissertations:

Doctoral dissertations: Yaglova N.V. “Morphological and biochemical study of the secretory activity of the thyroid gland in the experimental syndrome of non-thyroid diseases”, 2011; Obernikhin S. S. Postnatal morphogenesis of the immune system organs and skin of the offspring of female mice exposed to immunostimulation in early pregnancy, 2014.

Candidate: Timokhina E.P. “Morphofunctional changes in the organs of the immune system under prolonged exposure to low doses of DDT”, 2015; Sledneva Yu.P. “Age-related changes in the histophysiology of the thyroid follicular epithelium of male and female rats under the influence of the endocrine disruptor DDT”, 2017.

Main publications:

Yaglova N.V. Syndrome of non-thyroid diseases. M .: 4Mpress, 2013, –168s.

Yaglov V.V., Mikhailyuk I.A., Yaglova N.V. Biology of the diffuse endocrine epithelial system. Ivano-Frankivsk: Ed. “Symphony forte”, 2013. –168p.

Yaglova N.V., Obernikhin S.C. Development of the immune system of the offspring after immunostimulating effects in the early stages of pregnancy. Moscow. INFRA-M. 2017 .– 220s.

V.V. Yaglov, N.V. Yaglova Fundamentals of cytology, embryology and histology: textbook. Moscow. INFRA-M. 2017 .– 637s. Approved by the UMO of the Russian Federation for education in the field of veterinary medicine and animal science as a textbook for students of higher educational institutions studying in the specialty 36.05.01 – “Veterinary medicine” (qualification “Veterinarian”)

Yaglov V.V., Yaglova N.V. Basics of Histology. Moscow. INFRA-M. 2017 .– 634s.

What is the Endocrine System?

21.1: What is the endocrine system?

The endocrine system sends hormones – chemical signals – through the bloodstream to target cells – cells that are selectively affected by hormones. These signals are produced by endocrine cells, secreted into the extracellular fluid, and then propagated into the blood.Eventually, they diffuse out of the blood and bind to target cells that have special receptors to recognize hormones.

Alternative Routes

Although most hormones pass through the circulatory system to reach their target cells, there are also alternative routes of hormone delivery to target cells. Paracrine signaling sends hormones from the endocrine cell into the extracellular fluid, where they affect local cells.In a form of paracrine signaling called autocrine signaling, hormones secreted into the extracellular fluid affect the cells that secrete them.

Another type of signaling, synaptic signaling, involves the release of neurotransmitters from the terminals of neurons into the synapse – a specialized connection that transfers information between neurons, where they bind to receptors on neighboring neurons, muscle cells, and glands. In neuroendocrine signaling, neurosecretory cells secrete neurohormones that travel through the blood to act on target cells.In general, endocrine signaling has a slower effect than other types of signaling because it takes longer for hormones to reach target cells, but the effects usually last longer as well.

Hormone release

Hormones directly diffuse into the extracellular fluid surrounding the endocrine glands because they have no ducts. In comparison, exocrine glands, such as the salivary gland, have ducts that release a targeted dose directly to the surface or cavity.In addition to being located in specialized endocrine glands, endocrine cells can also be located in organs such as the stomach, among cells with different functions.

Target cells

The hormone has specific target cells that have receptors that recognize the hormone. It can be thought of as a lock and key, where the receptors on the target cell are a lock and recognize only the hormone, the key that suits it. Target cells can be very close to hormone-producing endocrine cells, or very far away, but must be transported through the bloodstream.For example, the enteroendocrine cells of the stomach and small intestine secrete hormones that can alter the secretion of gastric acid by stomach cells. On the other hand, hormones secreted by the pituitary gland, located at the base of the brain, can affect urine production by affecting kidney cells.

Additional reading literature

Jones, Christopher M., and Kristien Boelaert. “The Endocrinology of Aging: A Mini-Review.” Gerontology 61, no. 4 (2015): 291–300. [Source]

Yang, Oneyeol, Hye Lim Kim, Jong-Il Weon, and Young Rok Seo. “Endocrine-Disrupting Chemicals: Review of Toxicological Mechanisms Using Molecular Pathway Analysis.” Journal of Cancer Prevention 20, no. 1 (March 2015): 12-24. [Source]

90,000 of its functions and diseases – Federal State Budgetary Institution “NMITs TPM” of the Ministry of Health of Russia

The thyroid gland plays an important role in the work of our body, if it does not function properly, metabolic processes are disturbed, and other systems malfunction.It is no coincidence that one day of the year was dedicated to this organ – today, May 25, is World Thyroid Day.

Alla Petrovna Makarovskaya, an endocrinologist at the National Medical Research Center for Therapy and Preventive Medicine of the Russian Ministry of Health, spoke about how the thyroid gland works, what hormones it produces and what function it performs.

“The thyroid gland belongs to the largest endocrine glands, is located under the larynx, anterior to the trachea, consists of two lobes and an isthmus (has the shape of a butterfly).

The name “thyroid” was given to it by the anatomist Thomas Worth in 1656, the iron in its form reminded him of the shields of the warriors of Ancient Greece. And the first mention of the thyroid gland dates back to the 4th century BC. – they were found in the writings of Hippocrates and Plato, in the writings of physicians in Ancient Greece, India and Egypt. According to WHO statistics, among endocrine disorders, thyroid diseases are in second place after diabetes mellitus.

This butterfly gland has its own holiday: May 25 – World Thyroid Day.The date was proposed in 2008 by the European Thyroid Association.

The thyroid gland produces hormones: thyroxine (T4) and triiodothyronine (T3), which, released directly into the blood, affect all cells and tissues of the body, regulate the rate of various metabolic processes, thereby influencing the functions of all organs and systems.

In the blood, most of the thyroid hormones are bound to proteins, they are biologically inactive, and only a small protein-free fraction of hormones actively performs their functions (free T3 and free T4).The “conductor” of the entire endocrine system is the hypothalamic-pituitary system, which consists of two glands: the pituitary gland, located at the base of the brain, and the hypothalamus, located in the brain slightly above the pituitary gland.

The thyroid, pituitary, and hypothalamus work in concert to control thyroid hormone levels. If, for example, there are not enough thyroid hormones in the blood, the pituitary gland increases the production of its thyroid-stimulating hormone (or TSH), which stimulates an increase in the production of hormones by the gland.Once normal thyroid hormone levels are restored, TSH production slows down and approaches normal.

The state of normal functioning of the thyroid gland is called euthyroidism (“eu-” in translation from Greek means “good”, “normal”). If the thyroid gland does not produce enough hormones, then metabolic processes in the body slow down. This condition is called hypothyroidism.

If there are more thyroid hormones than necessary, the metabolism increases and the opposite condition to hypothyroidism develops – hyperthyroidism.

Symptoms of hypo- and hyperthyroidism are not specific only for thyroid dysfunction, they can be associated with completely different problems. In order to accurately assess the activity of the thyroid gland, it is enough to donate blood, in which the TSH level, free T4 and free T3 are primarily assessed.

The term “goiter” is an enlarged thyroid gland. Currently, an accurate method for determining its size and structure is ultrasound (ultrasound).Autoimmune diseases of the thyroid gland are widespread. Diseases of this type are diffuse toxic goiter (DTG) and autoimmune thyroiditis (AIT). Each of these occurs in about one in 100 people.

Other diseases of the thyroid gland are nodules, cancer, subacute thyroiditis. Fine-needle aspiration biopsy (TAB) is indicated for differential diagnosis of nodular goiter (thyroid nodules exceeding 1 cm in diameter).

To make an appointment with an endocrinologist at the Consultative and Diagnostic Center of the National Medical Research Center for Therapy and Preventive Medicine of the Ministry of Health of Russia, call 8 (495) 790-71-72.

90,000 Endocrinologist at the INMED clinic on Rachmaninov 3K in Penza

Endocrinology is one of the most rapidly developing branches of therapeutic medicine. This area of ​​medicine studies various aspects of internal diseases, including the pathology of carbohydrate metabolism, dysfunction of the adrenal glands, thyroid disease, etc.
Endocrinology is the study of the structure and function of the endocrine glands, the hormones they produce, and related human diseases.
The endocrine system is a complex of organs and tissues that are capable of synthesizing and secreting biologically active substances. These substances maintain the constancy of the internal environment of the body and allow you to adequately respond to changing conditions of the external environment. The endocrine system is closely related to other systems of the body. Their complex correct work allows you to maintain life and maintain health. It is worth noting that hormonal therapy, which is used in some cases with profile pathology, one way or another affects all tissues of the body without exception.
Many people think that an endocrinologist treats only diabetes mellitus and everything connected with it, but this is not so! Profile diseases are much more varied and more cunning, because they can hide behind the masks of other disorders.
The competence of an endocrinologist includes diagnostics and treatment of the following diseases:
– hypothalamic-pituitary: hyperprolactinemia, acromegaly, diabetes insipidus, hypopituitarism, etc .;
– thyroid gland: thyrotoxicosis syndrome, hypothyroidism syndrome, other disorders that occur without disrupting its functional activity;
– parathyroid glands and osteoporosis;
– carbohydrate metabolism: diabetes mellitus;
– adrenal glands: hypo- and hypercortisolism, adrenal tumors (pheochromocytoma, aldosteroma, incindentoloma, etc. )).
In addition, the endocrinologist diagnoses and treats:
– some gynecological problems: polycystic ovaries, amenorrhea, ovarian insufficiency, hormone-producing ovarian tumors;
– some andrological problems: gynecomastia, male infertility, age-related hypogonadism, etc.;
– Autoimmune polyendocrine syndromes and neuroendocrine tumors.
If the endocrine system is dysfunctional, the whole organism becomes disordered. Remember that the concepts of “hormonal disruption” or “hormone imbalance” do not exist, there are endocrine diseases.It is the endocrinologist who is able to determine at what level the “breakdown” has occurred. The endocrinologist will prescribe the necessary hormonal and instrumental examinations and determine the tactics of treatment.

Endocrine system and pregnancy

Dear women who have already become mothers, planning or now carrying their baby. Pregnancy is undoubtedly a difficult period in a woman’s life, accompanied by stress in all body systems.

The endocrine system “plays” one of the leading roles in the course and successful resolution of pregnancy.For example, the thyroid gland is “responsible” for the development of the fetal thyroid gland, its intrauterine growth, but its influence on the formation of the child’s nervous system is especially great. Lack of thyroid hormones in the mother, first of all, will lead to a delay in the development of the baby, including after birth; the pancreas is “responsible” for the exchange of sugars, the dynamics of weight work. It is also important that changes in carbohydrate and fat metabolism against the background of even a normally proceeding pregnancy are considered as strong diabetogenic factors.Therefore, a pathology such as pregnancy diabetes is often encountered, especially in overweight women.

The ovaries, adrenal glands, pituitary gland – the central endocrine gland and the newly formed endocrine organ – the placenta, also make their contribution during pregnancy, without which it is generally impossible to bear a child. Therefore, in order to avoid unpleasant health surprises during pregnancy, it is necessary to start preparing for it in advance, even if your unborn child will not be the firstborn in the family.

If you had a chronic endocrine pathology even before pregnancy, it is necessary with a doctor to seek compensation for the disease (especially in the case of diabetes mellitus, hypothyroidism, diphorous-toxic goiter, etc.), it is necessary to select the optimal dose of medications. In the future, during pregnancy, it is necessary to constantly be under the supervision of an endocrinologist, since the dose of drugs is adjusted every trimester of pregnancy, and in some diseases, even more often.

It is advisable to check with relatives, especially in the female line, the presence of endocrine pathology. But if before pregnancy you have not yet been observed by an endocrinologist, then the plan for examining the endocrine system may look like this: at 4-8 weeks, the function of the thyroid gland is specified (blood is taken for hormones – TSH, free T4, antibodies to thyroperoxidase, and with pronounced toxicosis the first half of pregnancy, accompanied by weight loss – antibodies to the TSH receptor.

At 10-12 weeks (again at 24-28 weeks), a carbohydrate sensitivity test is performed if the glucose level during pregnancy before meals is more than 5.3 mmol / l.And it is obligatory for all women with excess weight.

At 16-20 weeks (as well as at any time with ultrasound signs of fetal growth retardation), a test is taken for hCG (chorionic gonadotropin), alpha-fetoprotein. Weight gain is monitored monthly. On average, the weight gain should be no more than 1 kg. per month in the 1st trimester, no more than 2-3 kg. in the 2nd and 3rd trimester. In total, it should be no more than 10-12 kilograms for the entire pregnancy with a normal weight initially, no more than 7 kg. with obesity before pregnancy, no more than 17 kg.with a lack of weight before pregnancy.

Women with problems with conception, threats of miscarriage and other signs of deviations from the normal course of pregnancy need a more in-depth endocrinological examination.

Of course, of all of the above, a woman is most worried about weight gain. This indicator is influenced by many factors: the state of weight before pregnancy, the nature of the diet during pregnancy (especially if you are genetically prone to overweight).Therefore, it is undesirable to have fried, spicy, salinity in your diet, limit citrus fruits, exotic fruits, seafood, nuts, baked goods. It is worth giving preference to vegetables and fruits (apples, pears, etc.), boiled (steamed or baked in the oven) fish and meat, sour-milk products. Also, chronic diseases of internal organs directly affect weight gain. Especially the kidneys, the cardiovascular system, those that can lead to fluid retention, and this, in turn, to weight gain.The risk of weight gain is especially high in the second trimester of pregnancy. Therefore, if you still began to gain weight, then be prepared for the fact that the doctor will prescribe you a special unloading diet.

Do not forget about movement, unless, of course, physical activity is contraindicated for you for health reasons. It should be recognized that excessive weight gain is not a cosmetic defect. This is a sign of trouble in the body, affecting the risk of developing diabetes in pregnant women, arterial hypertension, weakness of labor, etc.

During the feeding process, the baby’s weight should also be monitored. But it is worth starting to lose weight no earlier than six months after the completion of feeding. Fitness is contraindicated in a nursing woman, as the increased amount of stress hormones produced during sports can cause pain in the baby’s abdomen and constant anxiety. Naturally, during this period, the use of drugs that reduce weight is contraindicated.

In recent years, many pregnant women have been increasingly prescribed thyroid hormone preparations (L-thyroxine, eutirox).These drugs are prescribed so that the lack of the mother’s hormones does not affect the development of the child. Therefore, at least 3 times during pregnancy, you will have to control your hormonal background and visit an endocrinologist.