How Does the Endocrine System Maintain Homeostasis

Reviewed by: BD Editors

Last Updated: April 15, 2018

The endocrine system consists of ductless glands that secrete hormones into the blood stream. These hormones drive the homeostatic feedback loops that keep the body healthy and in equilibrium. The endocrine system is intimately integrated into physiological processes in order for it to carry out its functions.

The major endocrine glands in humans are the pituitary gland, pineal gland, ovaries, testes, pancreas, thyroid, parathyroid, and the adrenals. The hypothalamus-pituitary complex in the brain is the main neural control center for all endocrine glands and systems. Several organs in the body have secondary endocrine functions such as the heart, gonads, bones, kidneys, and liver. In addition to their homeostatic functions, hormones coordinate growth, reproduction and many other processes.

Hypothalamus-Pituitary Complex

This control center in the brain secretes hormones that have direct effects on tissues and also secretes hormones that regulate the production and secretion of hormones in other glands. Also, this is the main area where the chemical messages of the endocrine and nervous systems are coordinated. In other words, there are many examples where a stimulus from the nervous system is routed through the complex and “translated” before hormones are secreted in response.

Hormones secreted by the hypothalamus and some of their effects are:

• Dopamine – Modulates motor-control centers (loss of dopamine results in Parkinson’s disease).
• Somatostatin – Inhibits the release of growth hormone and thyroid-stimulating hormone.
• Corticotropin-releasing hormone – Causes the release of adrenocorticotropic hormone from the pituitary gland in response to stress, which stimulates the release of cortisol.
• Thyrotropin-releasing hormone – Causes release of thyrotropin hormone from the pituitary which stimulates the thyroid to release thyroxine and triiodothyronine, affecting metabolism all over the body.

Hormones secreted by the pituitary gland and some of their effects are:

• Thyroid stimulating hormone – Stimulates the thyroid gland to release thyroid hormone.
• Antidiuretic hormone – Causes water to be reabsorbed by the kidneys.
• Oxytocin – Causes contractions of the uterus during childbirth.
• Melanocyte-stimulating hormone – Stimulates melanin formation in melanocyte cells.

The image above shows the locations of the hypothalamus and pituitary glands in the human brain.

Feedback Loops

Positive and negative feedback loops are essential for homeostasis in the human body. They provide the controls needed to keep the effects of hormones and hormone chain reactions from spiraling out of control.

Negative feedback loops act to reverse changes in the body’s physiological condition. For example, cells in the pancreas detect a rise in blood glucose levels. This stimulus causes beta cells in the pancreas to release insulin which causes muscles, fat cells, and liver cells to take in the glucose. The negative feedback begins when blood glucose decreases. Alpha cells in the pancreas then inhibit the release of insulin from beta cells. This is a dynamic process that goes on all the time to maintain homeostasis of blood glucose levels.

A positive feedback loop like full-term childbirth intensifies the change in the body’s physiological condition and is considered normal as long as there is an endpoint. In childbirth, the cervix stretches as the baby moves down the birth canal. Stretch receptors in the cervical tissue send messages to the brain which triggers the release of oxytocin. Oxytocin makes the mother’s contractions stronger, stretching the cervix more and pushing the baby farther down the birth canal. This cycle continues until the baby is born and stimulation of the stretch receptors in the cervix stops sending signals to the mother’s brain.

References

• OpenStax College. (2018). Anatomy & Physiology. Houston, TX. OpenStax CNX. Retrieved from http://cnx.org/contents/[email protected]
• Endocrine System. (n.d.). In Wikipedia. Retrieved April 9, 2018 from https://en.wikipedia.org/wiki/Endocrine_system

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endocrine system – Students | Britannica Kids

Introduction

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The endocrine system is a body system in animals. It controls and regulates body processes by means of chemical messengers called hormones. The system is composed of a group of ductless glands located throughout the body that produce hormones in response to the body’s needs. Once released, hormones may act on nearby structures, or they may travel in the blood to distant target organs. The glands of the endocrine system are interdependent, forming one of the most complex systems in the body. Although each gland has its own function, that function depends on the activities of another gland.

The task of the endocrine system is to maintain homeostasis, or balance, in the body. Because hormones have a powerful effect on the body, the production and release of these messengers is tightly regulated. Too much or too little of any hormone may cause the body to function improperly; in some cases this may result in disease or even death.

All vertebrates have an endocrine system, as do many invertebrates, though the systems vary in many respects. The endocrine systems of humans and other mammals are very similar, however, and are the focus of this article.

Endocrine Glands

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The major endocrine glands of mammals are the hypothalamus, pituitary, pineal, thyroid, parathyroids, thymus, pancreas, adrenals, and gonads (ovaries and testes). Some nonendocrine organs also make hormones; these include the stomach, small intestine, and kidneys. The placenta of pregnant mammals has an endocrine function. It produces hormones that influence uterine, fetal, and ovarian processes.

Hypothalamus

The hypothalamus is a small structure located near the base of the brain that plays a key role in regulating many body processes. The hypothalamus affects the endocrine system primarily through control of the pituitary gland via production of “releasing hormones.” These messengers are so-named because they stimulate the release of hormones made in the pituitary. For example, thyrotropin-releasing hormone (TRH) is made and released by the hypothalamus. TRH travels to the pituitary, where it stimulates production of thyrotropin, or thyroid-stimulating hormone (TSH). TSH travels via the blood to the thyroid gland, where it stimulates production of the hormone thyroxine. This pathway can be summarized as follows:

The hypothalamus also produces two hormones, vasopressin and oxytocin, that act directly on distant target organs. Vasopressin, also called antidiuretic hormone (ADH), helps the body conserve water. Specifically, it prevents the kidneys from producing too much urine. Inadequate vasopressin causes the condition diabetes insipidus, which is characterized by excessive production of very dilute urine. Oxytocin is critical during and after childbirth. It causes muscle contractions in the uterus and stimulates milk flow from the mother’s breasts. Though produced by the hypothalamus, both hormones are stored in and regulated by the pituitary gland.

Pituitary Gland

The pituitary gland is a small, oval structure under the brain. It has two parts—the anterior lobe and the posterior lobe. The pituitary influences the activity of many other endocrine glands. Because most pituitary hormones are made in the anterior lobe, the anterior pituitary is often called the “master” gland of the body. Growth hormone (GH), prolactin, adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) are among the many hormones produced in the anterior pituitary. The posterior lobe of the pituitary does not produce hormones. It merely stores and releases the hypothalamus hormones vasopressin and oxytocin.

Nearly all the anterior pituitary hormones act on specific target tissues or organs. Prolactin controls the development, growth, and milk production of the mammary glands. ACTH stimulates the adrenal glands to produce steroid hormones such as cortisol. TSH prompts the thyroid gland to produce thyroxine. FSH and LH together induce the gonads—ovaries and testes—to make sex hormones.

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Growth hormone (GH) targets all of the body’s tissues, including bone. GH works by stimulating growth at the cellular level. The pituitary must secrete the correct amount of GH for normal early growth. If too little GH is produced in infancy and childhood, dwarfism occurs. If too much GH is produced in early life, gigantism results. Excess GH produced in an adult leads toacromegaly, an enlargement of the jaw and the extremities.

Pineal Gland

The pineal gland is a pea-sized endocrine gland located in the center of the brain. The pineal secretes the hormone melatonin, which helps maintain the body’s daily sleep/wake cycle. The pineal produces melatonin in response to changes in light. When the retina of the eye detects light, melatonin production is inhibited; this helps maintain wakefulness. When the environment grows dark, melatonin production is stimulated; this causes the body to prepare for sleep.

Thyroid Gland

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The thyroid gland lies on both sides of the trachea in the neck. Its two lobes are connected by an isthmus and resemble the letter H. Thyroid-stimulating hormone (TSH) from the pituitary gland stimulates the thyroid to make thyroid hormone. Thyroid hormone has two forms—thyroxine and triiodothyronine. The forms have similar actions and differ mainly in chemical structure and in how they circulate in the body. The main task of thyroid hormone is to regulate the body’s metabolism.

Overproduction of thyroid hormone causes the condition hyperthyroidism. The increase in thyroid hormones causes the metabolic rate to skyrocket, often producing heart problems, heat intolerance, and weight loss. Underproduction of thyroid hormone causes hypothyroidism, characterized by a general sluggishness of mind and body; common signs include fatigue, cold intolerance, and weight gain. Hypothyroidism in infants, though treatable, can in some instances cause severe intellectual disability and slowed growth resulting in dwarfism. The most severe form of this is the condition cretinism.

The thyroid gland also makes calcitonin, a hormone that lowers blood concentrations of calcium and phosphate when they rise above normal. Calcitonin activity counters the actions of parathyroid hormone, which increases blood calcium and phosphate levels when they are too low.

Parathyroid Glands

The parathyroid glands are located next to or embedded within the thyroid gland. Humans and other mammals usually have four parathyroid glands. The glands secrete parathyroid hormone (also called parathormone), which increases calcium and phosphate levels in the blood when they fall too low. Parathyroid hormone activity thus counters that of calcitonin, which acts to lower calcium and phosphate levels. Both parathyroid hormone and calcitonin are essential for maintaining normal calcium and phosphate levels in the body.

Overproduction of parathyroid hormone causes hyperparathyroidism, which generally produces nonspecific symptoms such as fatigue, weakness, and appetite loss. Severe cases can lead to kidney stones or osteoporosis (a disease involving the thinning of bones). Underproduction of the hormone causes hypoparathyroidism, which may cause severe muscle cramping and twitching.

Thymus

The thymus is a pyramid-shaped organ located in the chest. The thymus is mainly a lymphoid organ—it is composed mainly of lymphoid tissue and so is part of the immune system. However, the thymus also contains some endocrine tissue that produces several hormones that help stimulate T-cell production. (T cells are a type of white blood cell that is essential to the immune system.) The two best-studied thymic hormones are thymosin and thymopoietin. The thymus is very active during infancy and childhood but gradually shrinks in size and influence after puberty.

Pancreas

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The pancreas is a long, narrow organ located in the abdomen. The pancreas is part of both the digestive system and the endocrine system. In its endocrine role, the pancreas secretes the hormones insulin and glucagon, which regulate glucose levels in the blood. Insulin and glucagon affect nearly every cell in the body because the regulation of glucose is essential for cells to function properly (see cellular respiration).

The action of each of these hormones counters that of the other. Insulin works to lower blood glucose levels when they are too high, whereas glucagon works to raise blood glucose levels when they are too low. Lack of insulin causes diabetes mellitus, a common but potentially fatal ailment. Hyperinsulinism is a genetic condition in which the body secretes too much insulin. This causes blood glucose levels to plummet, causing a condition called hypoglycemia. In infants and children, untreated hypoglycemia can cause seizures and possibly brain damage.

In the pancreas, insulin is produced by beta cells and glucagon by alpha cells. The cells lie close together in clusters called the islets of Langerhans, which are found throughout the pancreas. The islets also include delta cells—these produce the hormone somatostatin. Somatostatin inhibits the activity of several hormones, including insulin, glucagon, and growth hormone. (See also gland.)

Adrenal Glands

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The adrenal glands produce a variety of hormones that help regulate metabolism and blood pressure, as well as many essential activities. The adrenal glands lie on top of the kidneys. Each gland consists of two regions—an outer cortex and an inner medulla. Each region produces different types of hormones.

When stimulated by adrenocorticotropic hormone (ACTH), the adrenal cortex makes steroid hormones, a group of hormones that are synthesized from cholesterol. Among the most important of these are cortisol and aldosterone. Cortisol is critical for the body’s stress response. It helps maintain blood glucose concentrations and blood pressure through a series of complex processes. Cortisol also has powerful anti-inflammatory and anti-allergy actions. Aldosterone helps regulate salt and water balance, which help maintain normal blood pressure and fluid volume.

Overproduction of adrenal cortex hormones, especially cortisol, cause Cushing syndrome. This disorder is characterized by abnormal weight gain, especially in the abdomen and face. Thinning of the skin, bruising, and high blood pressure also are common. Underproduction of cortisol and aldosterone results in Addison disease. This disorder is marked by low blood pressure, weakness, and weight loss, among other symptoms. Addison disease is fatal if it is not diagnosed and treated. Both Cushing syndrome and Addison disease are rare disorders.

The adrenal medulla produces the hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). Epinephrine triggers the responses needed to combat fear, shock, cold, or fatigue. Both hormones raise blood pressure and increase heartbeat. Under their influence, glycogen in the liver and muscles is converted to glucose for additional energy when the body is under severe stress.

Gonads

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The gonads—the ovaries in females and the testes in males—make steroid hormones that control sexual development and functions. Production and release of these hormones is controlled in both males and in females by two anterior-pituitary hormones—follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones work together to regulate the gonads. Luteinizing hormone is also known as interstitial cell-stimulating hormone, or ICSH.

In females, FSH and LH are activated each month as part of the female reproductive cycle (see menstruation). Together, they stimulate development of an ovarian follicle—a small pocket of cells in the ovary that contains a single ovum, or egg cell. Under the influence of FSH and LH, the follicle grows until it bursts and releases the egg. The egg then moves down one of the two oviducts, where it may be fertilized by a sperm. Meanwhile, the ruptured follicle changes into a corpus luteum. This tiny structure then produces progesterone, a steroid hormone needed for maintaining pregnancy. If fertilization does not occur, the corpus luteum degenerates. The ovaries also produce estrogen, a steroid hormone that influences development of female secondary sexual characteristics, such as body form and voice pitch. The ovaries produce estrogen on a continual basis, though levels rise and fall at different points during the female’s monthly reproductive cycle. During pregnancy, the placenta also produces estrogen.

In males, FSH and LH work together to stimulate development of the testes and the male reproductive system. FSH promotes the development of tubules in the testes and promotes development and maturation of sperm. LH stimulates the testes to secrete testosterone, a steroid hormone. Testosterone influences development of the male sex organs. It also promotes development of male secondary sexual characteristics, such as facial hair and the deepening of the voice.

Feedback Control of Hormone Secretion

The endocrine system is controlled by complex feedback mechanisms in which the secretion of a hormone is turned on (stimulated) or turned off (inhibited), depending on its concentration. Such feedback mechanisms help the body maintain homeostasis. There are two types of feedback control mechanisms—negative feedback and positive feedback.

Negative Feedback

Negative feedback helps to maintain homeostasis by keeping hormone levels within a narrow range. In a negative feedback mechanism, high levels of a hormone turn off further release of that hormone. This usually occurs in a stepwise pattern: the high concentration of the hormone signals back through the system to turn off production of the hormone or hormones that stimulated its release.

The TRH-TSH-thyroxine system described in the section Hypothalamus is a classic example of negative feedback. High levels of thyroxine in the blood signal the hypothalamus to stop releasing TRH. Without TRH, the anterior pituitary stops producing TSH. Without TSH, the thyroid stops releasing thyroxine. When thyroxine levels drop below normal, the body signals the hypothalamus to turn on production of TRH. TRH signals the pituitary to release TSH, and TSH then stimulates the thyroid to produce thyroxine.

Positive Feedback

Positive feedback produces a response that continues to increase in order to produce the desired effect. In this mechanism, the activity of a hormone signals the system to produce and release more of the hormone.

An example of a positive feedback mechanism is the release and response of oxytocin during childbirth. The first contractions of the uterus signal the body to release oxytocin. Oxytocin travels to the uterus, where it stimulates more contractions. The contractions signal back to the body to release more oxytocin, which stimulates more contractions, and so on. The feedback loop continues until the child is born—the contractions stop, signaling the body to stop releasing oxytocin.

What affects hormones? How does the endocrine system work? — Art Life blog

There are no organs of greater or lesser importance in the human body, it is a single multifunctional system in which everything is interconnected. An important role in ensuring the fine regulation of human vital processes is played by the health of the endocrine glands, or in other words, the endocrine system. This is a complex system with a three-level hierarchy that governs all subcortical acts of life support (that is, actions that occur outside the control of the cerebral cortex): hunger, thirst, satiety, sweating, the ability to procreate. The function of the endocrine system is to ensure the constancy of the internal environment of the body by maintaining the physiological level of substances in the blood.

The hypothalamus is located in the brain and produces special substances – liberins, which act as signal molecules on the underlying pituitary gland, ensuring the production and distribution of hormones in the right amount and at the right time. The pituitary gland is a gland that secretes a large amount of hormones that stimulate the work of other endocrine glands. These hormones are called tropins, or triple hormones, which means that they have an affinity for a specific target organ. Thyrotropic hormone activates the production of hormones by the thyroid gland, luteotropic hormone – the formation of the corpus luteum and the production of progesterone (the hormone that fixes pregnancy), adrenocorticotropic hormone activates the adrenal gland and the production of adrenaline and cortisol, stress hormones.

The endocrine glands located on the lower level of the hierarchy of the system, having received a signal from the pituitary gland, begin the production of hormones that perform a regulatory function. The work of these glands is controlled by a biofeedback mechanism. The level of the hormone produced in the blood at a certain concentration serves as a signal to stop the production of the hormone by the gland. And vice versa, its lack in the blood will be constantly replenished with more and more new production of the hormone.

If you take a closer look at the functions of the executing glands, it becomes clear how important a factor is the presence of the correct feedback in the regulation of not only the activity of the glands themselves, but also the performance of the body as a whole.

Let’s dwell on some endocrine glands

The thyroid gland, located in the front of the neck, secretes three hormones containing iodine, which are responsible for metabolism, which determines the work of each internal organ, the rate of protein production, memory functions, emotions , as well as intelligence and reproductive viability. In the event of a lack of iodine in the diet, which is necessary for the synthesis of hormones of this gland, it does not receive a feedback signal about the saturation of the blood with hormones and continues to produce them. As a result, gland tissue (goiter) can grow.

Adjacent to the thyroid gland are four small parathyroid glands involved in calcium metabolism. There are different opinions about the causes of dysfunction of these glands. But many reputable scientists cite dietary calcium deficiency as a risk factor. Its deficiency can provoke an excess production of the hormone by the parathyroid glands, which will lead to its washing out of the bones until the gland receives a biofeedback signal in the form of a physiological level of calcium in the blood.

The pancreas as an endocrine organ produces two hormones: insulin and glucagon, which regulate carbohydrate metabolism. The adrenal glands are two small glands, located one above each kidney and consisting of two independent parts – the cortex and the medulla. These glands produce adrenaline, cortisol (stress hormones) and hormones that regulate water-salt metabolism in the body. Using the example of the interaction of the pancreas and adrenal glands, it is easy to demonstrate the absolute relationship of all glands of the endocrine system and their functions. It is known that under stress, a lot of adrenaline and cortisol are released into the blood, chronic stress is no exception. It is also known that a high level of stress hormones blocks the synthesis of insulin, and at a certain point in time, its decrease can become critical and lead to the development of diabetes mellitus (an endocrine disease in which a lack of insulin in the blood makes it impossible for cells to absorb incoming glucose).

This example clearly illustrates that in the modern world it is impossible to ignore the need for timely attention and support in relation to the endocrine system. You can not smoke or abuse alcohol, but even this does not provide absolute protection against adverse risk factors that disrupt the functions of the endocrine system. Among them: stress, infectious diseases (acute and chronic), physical inactivity and improper diet and type of nutrition – in a word, everything that accompanies the life of a city dweller of working age. And since up to 80% of the inhabitants of the Earth live in cities, it is appropriate to ask the question: is there a way to universally prevent diseases and dysfunctions of the glands of the endocrine system?

Yes, absolutely! Based on the diversity of the chemical structure of hormones and the functions of the glands that produce them, the first place among the measures that help maintain the health of the endocrine system should be given to the daily diet. Ideally, it should be balanced in amino acids, phospholipids, and unsaturated fats. Particular attention is paid to the adequate content of iodine. Daily intake of dietary fiber, the presence of hepatoprotectors and antioxidants in the diet, the rejection of alcohol abuse and excessive consumption of sugar-containing foods are additional steps in strengthening all levels of the endocrine system. All of these substances are food components on which the formulations of Artlife bioactive complexes are built. Their purpose is to form the foundation of health through a competent impact on the diet, through filling it with substances that support the physiological level of regulatory processes responsible for replenishing the body’s resources, increasing adaptive capabilities. And since the endocrine system is one of the main regulatory systems of the body, strengthening it is nothing more than prolonging life itself.

Natalia SHILOVA

Endocrine system | Regional Budgetary Institution “Center for Assistance to Family and Children “Great Bear” branch N1 Crisis Center for Assistance to Family and Children

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September 2, 2019

The endocrine system is formed by a combination of endocrine glands (endocrine glands) and a group of endocrine cells scattered throughout various organs and tissues that synthesize and release into the blood highly active biological substances – hormones that have a stimulating or suppressing effect on body functions: metabolism and energy, growth and development, reproduction and adaptation to living conditions. The function of the endocrine glands is under the control of the nervous system.

Any malfunction of the endocrine system leads to the development of the disease. The most common diseases of the endocrine system are distinguished:

Hypothyroidism is a disease caused by hypofunction of the thyroid gland, when an insufficient amount of hormones is produced. The disease is characterized by a slowdown in metabolic processes, which leads to a number of symptoms, which at the initial stage are attributed to ordinary fatigue. Women are more likely to suffer from hypothyroidism than men – in the fair sex, the disease is observed in 19times more often.

The severity of symptoms depends on the degree of dysfunction of the thyroid gland. Hypothyroidism usually develops gradually. Patients do not notice the symptoms of the disease for a long time and do not go to the doctor.

Manifestations of hypothyroidism are many-sided , individual symptoms are non-specific:

• obesity, decrease in body temperature, chilliness – a constant feeling of cold due to a slowdown in metabolism, yellowness of the skin, hypercholesterolemia, early atherosclerosis;
• myxedematous edema: swelling around the eyes, teeth marks on the tongue, difficulty in nasal breathing and hearing loss (swelling of the mucous membranes of the nose and auditory tube), hoarseness of voice;
• drowsiness, slowness of mental processes (thinking, speech, emotional reactions), memory loss, polyneuropathy;
• shortness of breath, especially when walking, sudden movements, pain in the region of the heart and behind the sternum, myxedema heart (decreased heart rate, increased heart size), hypotension;
• tendency to constipation, nausea, flatulence, enlarged liver, biliary dyskinesia, cholelithiasis; anemia;
• dryness, brittleness and hair loss, brittle nails with transverse and longitudinal grooves;
• menstrual irregularities in women.