Interactive Guide to the Endocrine System | Internal body (2023)

The endocrine system includes all the glands in the body and the hormones produced by these glands. The glands are controlled directly by stimulation from the nervous system as well as chemical receptors in the blood and hormones produced by other glands. By regulating the functions of the organs in the body, these glands help maintain the body's homeostasis. Cellular metabolism, reproduction, sexual development, sugar and mineral homeostasis, heart rate, and digestion are among the many processes regulated by the actions of hormones.

Anatomy of the Endocrine System

Hypothalamus

Thehypothalamusis part of itbrainlocated above and in front of the brainstem and below thechamber. It serves many different functions in thenervous system, and is also responsible for direct control of the endocrine system through the pituitary gland. The hypothalamus contains special cells called neurosecretory cells - neurons that secrete hormones:

• Thyrotropin Releasing Hormone (TRH)
• Growth Hormone Releasing Hormone (GHRH)
• Growth hormone inhibiting hormone (GHIH)
• Gonadotropin Releasing Hormone (GnRH)
• Corticotropin releasing hormone (CRH)
• Oxytocin
• antidiuretic hormone (ADH)

All releasing and inhibiting hormones affect the function of the anterior pituitary gland. TRH stimulates the anterior pituitary gland to release thyroid-stimulating hormone. GHRH and GHIH regulate the release of growth hormone—GHRH stimulates the release of growth hormone, GHIH inhibits its release. GnRH stimulates the release of follicle-stimulating hormone and luteinizing hormone while CRH stimulates the release of adrenocorticotropic hormone. The last two hormones - oxytocin and antidiuretic hormone - are produced by the hypothalamus and transported to the posterior pituitary, where they are stored and later released.

Mucous membrane

Themucosa, also known as the pituitary gland, is a small pea-sized piece of tissue attached to the lower part of the brain's hypothalamus. Manyblood vesselsthey surround the pituitary gland to carry the hormones it releases throughout the body. It is in a slight depression atsphenoid bonecalled the sella turcica, the pituitary gland is actually made up of 2 completely separate structures: the posterior and the anterior pituitary gland.

Posterior pituitary

The posterior pituitary is actually not glandular tissue at all, but nervous tissue. The posterior pituitary is a small extension of the hypothalamus through which the axons of some of the neurosecretory cells of the hypothalamus extend. These neurosecretory cells create 2 hormones in the hypothalamus that are stored and released by the posterior pituitary gland:

• Oxytocin triggers uterine contractions during labor and the release of milk during breastfeeding.
• Antidiuretic hormone (ADH) prevents water loss in the body by increasing water reabsorption by the kidneys and decreasing blood flow to the sweat glands.

Anterior pituitary gland

The anterior pituitary gland is the actual glandular part of the pituitary gland. The function of the anterior pituitary gland is controlled by the releasing and inhibiting hormones of the hypothalamus. The anterior pituitary gland produces 6 important hormones:

• Thyroid-stimulating hormone (TSH), as its name suggests, is a tropic hormone responsible for stimulating the thyroid gland.
• Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex, the outer part of the adrenal gland, to produce its hormones.
• Follicle-stimulating hormone (FSH) stimulates the follicle cells of the gonads to produce gametes - eggs in females and sperm in males.
• Luteinizing hormone (LH) stimulates the gonads to produce the sex hormones - estrogen in women and testosterone in men.
• Human growth hormone (HGH) affects many target cells throughout the body by stimulating their growth, repair and reproduction.
• Prolactin (PRL) has many effects on the body, the main of which is that it stimulates themammary glandsof the breast to produce milk.

Epiphysis

Theepiphysisit is a small, pine-shaped mass of glandular tissue located just behind the ventricle of the brain. The pineal gland produces the hormone melatonin that helps regulate the human sleep-wake cycle, known as the circadian rhythm. The activity of the pineal gland is inhibited by stimulation from retinal photoreceptors. This sensitivity to light causes melatonin to be produced only in low light or darkness. Increased melatonin production causes people to feel sleepy at night when the pineal gland is active.

Thyroid gland

Thethyroid glandis a butterfly-shaped gland located at the base of the throat and wraps around the lateral sides of the trachea. The thyroid gland produces 3 main hormones:

• Calcitonin
• Triiodothyronine (T3)
• Thyroxine (T4)

Calcitonin is released when calcium ion levels in the blood rise above a certain set point. Calcitonin works to reduce the concentration of calcium ions in the blood by aiding the absorption of calcium into the bone matrix. The hormones T3 and T4 work together to regulate the body's metabolic rate. Increased levels of T3 and T4 lead to increased cellular activity and energy use in the body.

Parathyroid glands

Theparathyroid glandsare 4 small masses of glandular tissue located on the back of the thyroid gland. The parathyroid glands produce the hormone parathyroid hormone (PTH), which is involved in calcium ion homeostasis. PTH is released by the parathyroid glands when blood calcium ion levels fall below a set point. PTH stimulates osteoclasts to break down calcium-containing bone matrix to release free calcium ions into the bloodstream. PTH also triggers the kidneys to return calcium ions that have been filtered from the blood back into the bloodstream, so that it is conserved.

Adrenal glands

Theadrenal glandsare a pair of roughly triangular glands located immediately superior to the kidneys. The adrenal glands are each made up of 2 distinct layers, each with their own unique functions: the outer adrenal cortex and the inner medulla.

Adrenal cortex

The adrenal cortex produces many cortical hormones in 3 categories: glucocorticoids, mineralocorticoids, and androgens.

• Glucocorticoids have many different functions, including breaking down proteins and lipids to produce glucose. Glucocorticoids also work to reduce inflammation and the immune response.
• Mineralocorticoids, as their name suggests, are a group of hormones that help regulate the concentration of mineral ions in the body.
• Androgens, such as testosterone, are produced at low levels in the adrenal cortex to regulate the growth and activity of cells that are receptive to male hormones. In adult men, the amount of androgens produced by the testes is many times greater than the amount produced by the adrenal cortex, resulting in secondary male sex characteristics.

Adrenal medulla

The adrenal medulla produces the hormones epinephrine and norepinephrine under stimulation from the sympathetic division of the autonomic nervous system. Both of these hormones help increase blood flow to the brain and muscles to improve the fight-or-flight response to stress. These hormones also work to increase heart rate, breathing rate, and blood pressure, while decreasing blood flow and the function of organs not involved in emergency response.

Pancreas

Thepancreasis a large gland located in the abdominal cavity just below and behind thestomach. The pancreas is considered a heterocrine gland as it contains both endocrine and exocrine tissue. Pancreatic endocrine cells make up only about 1% of the total mass of the pancreas and are found in small clusters throughout the pancreas called islets of Langerhans. Within these islets there are 2 types of cells - alpha and beta cells. Alpha cells produce the hormone glucagon, which is responsible for raising blood glucose levels. Glucagon triggers muscle and liver cells to break down the polysaccharide glycogen to release glucose into the bloodstream. Beta cells produce the hormone insulin, which is responsible for lowering blood glucose levels after a meal. Insulin triggers the absorption of glucose from the blood into the cells, where it is added to glycogen molecules for storage.

Gonads

The gonads—the ovaries in women and the testicles in men—are responsible for producing the body's sex hormones. These sex hormones determine the secondary sex characteristics of adult females and adult males.

• Bullocks: THEbullocksare a pair of ellipsoidal organs located in the scrotum of males that produce the androgen testosterone in males after the onset of puberty. Testosterone affects many parts of the body, including muscles, bones, genitals and hair follicles. This hormone causes bone and muscle growth and strength, including accelerated growth of long bones during puberty. During puberty, testosterone controls the growth and development of male genitalia and body hair, including pubic, chest, and facial hair. In men who have inherited baldness genes, testosterone triggers the onset of androgenetic alopecia, commonly known as male pattern baldness. (Read usHis criticismfor an unbiased look at one way you can treat and reverse male pattern baldness.)
• Ovaries: THEovariesare a pair of tonsils located in the pelvic cavity lateral to and above the uterus in women. The ovaries produce the female hormones progesterone and estrogen. Progesterone is most active in women during ovulation and pregnancy, where it maintains the right conditions in the human body to support a developing fetus. Estrogens are a group of related hormones that act as the primary female sex hormones. The release of estrogen during puberty triggers the development of secondary female sex characteristics, such as uterine growth, breast development, and pubic hair growth. Estrogen also triggers the increased bone growth during puberty that leads to adult height and proportions.

Anger

Theangeris a soft, triangular-shaped organ located in the chest behind the sternum. The thymus produces hormones called thymosins that help train and develop T-lymphocytes during fetal development and childhood. T-lymphocytes produced in the thymus protect the body from pathogens throughout a person's life. The thymus is dormant during adolescence and is slowly replaced by adipose tissue throughout a person's life.

Other organs that produce hormones

In addition to the glands of the endocrine system, many other non-glandular organs and tissues of the body also produce hormones.

• Heart: Its cardiac muscle tissueheartis capable of producing the hormone atrial natriuretic peptide (ANP) in response tohigh blood pressureflat. ANP works to lower blood pressure by causing vasodilation to provide more room for blood to pass through. ANP also reduces blood volume and pressure by causing the kidneys to excrete water and salt from the blood.
• Kidneys: THEkidneysthey produce the hormone erythropoietin (EPO) in response to low blood oxygen levels. EPO released from the kidneys travels to the red bone marrow where it stimulates increased production of red blood cells. The number of red blood cells increases the oxygen-carrying capacity of the blood, eventually ending the production of EPO.
• Digestive system: The hormones cholecystokinin (CCK), secretin and gastrin are all produced by the organs of the gastrointestinal tract. CCK, secretin, and gastrin help regulate the secretion of pancreatic juice, bile, and gastric juice in response to the presence of food in the stomach. CCK also plays an important role in the feeling of satiety or "fullness" after eating.
• Adipose: Adipose tissue produces the hormone leptin which is involved in the management of appetite and energy use by the body. Leptin is produced at levels relative to the amount of adipose tissue in the body, allowing the brain to monitor the body's energy storage status. When the body contains a sufficient level of fat to store energy, the level of leptin in the blood tells the brain that the body is not starving and can function normally. If the level of adipose fat or leptin drops below a certain threshold, the body enters a state of starvation and tries to conserve energy through increased hunger and food intake and decreased energy use. Adipose tissue also produces very low levels of estrogen in both men and women. In obese individuals the large volume of adipose tissue can lead to abnormal estrogen levels.
• Placenta: In pregnant women, the placenta produces several hormones that help maintain the pregnancy. Progesterone is produced to relax the uterus, protect the fetus from the motherimmune systemand prevent premature delivery of the fetus. Human chorionic gonadotropin (HCG) assists progesterone by signaling the ovaries to maintain estrogen and progesterone production throughout pregnancy.

• Topical hormones: Prostaglandins and leukotrienes are produced by every tissue in the body (except blood tissue) in response to noxious stimuli. These two hormones mainly affect the cells that are local to the source of the damage, leaving the rest of the body free to function normally.

  1. Prostaglandins cause swelling, inflammation, increased sensitivity to pain, and increased local body temperature to help block damaged areas of the body from infection or further damage. They act as the body's natural bandages to keep pathogens out and swell around damaged joints like a natural plaster to limit movement.
  2. Leukotrienes help the body heal after prostaglandins kick in by reducing inflammation while helping white blood cells move into the area to clean up pathogens and damaged tissue.

Physiology of the Endocrine System

Endocrine System vs. Nervous System Function

The endocrine system works alongside the nervous system to form the body's control systems. The nervous system provides a very fast and tightly targeted system to activate specific glands and muscles throughout the body. The endocrine system, on the other hand, is much slower acting, but has very widespread, long-lasting and powerful effects. Hormones are distributed from the glands through the bloodstream throughout the body, affecting any cell with a receptor for a particular hormone. Most hormones affect cells in many organs or throughout the body, leading to many different and powerful responses.

Properties of hormones

Once the hormones have been produced by the glands, they are distributed through the body via the bloodstream. As hormones travel through the body, they pass through cells or across cell plasma membranes until they encounter a receptor for that particular hormone. Hormones can only affect target cells that have the appropriate receptors. This property of hormones is known as specificity. Hormonal specificity explains how each hormone can have specific effects on widespread parts of the body.

Many hormones produced by the endocrine system are classified as tropic hormones. A tropic hormone is a hormone that is able to trigger the release of another hormone in another gland. Tropic hormones provide a control pathway for hormone production as well as a way to control glands in distant areas of the body. Many of the hormones produced by the pituitary gland, such as TSH, ACTH, and FSH are tropic hormones.

Hormonal Regulation

Hormone levels in the body can be regulated by several factors. The nervous system can control hormone levels through the action of the hypothalamus and its releasing and inhibiting hormones. For example, TRH produced by the hypothalamus stimulates the anterior pituitary to produce TSH. Tropic hormones provide another level of control over hormone release. For example, TSH is a tropic hormone that stimulates the thyroid gland to produce T3 and T4. Diet can also control hormone levels in the body. For example, the thyroid hormones T3 and T4 require 3 or 4 iodine atoms, respectively, to be produced. In people who lack iodine in their diet, they will not produce sufficient levels of thyroid hormones to maintain a healthy metabolic rate. Finally, the number of receptors present on cells can vary from cell to cell in response to hormones. Cells exposed to high levels of hormones for prolonged periods of time can begin to reduce the number of receptors they produce, leading to reduced hormonal control of the cell.

Categories of Hormones

Hormones are classified into 2 categories according to their chemical composition and solubility: water-soluble and fat-soluble hormones. Each of these classes of hormones has specific mechanisms of action that dictate how they affect their target cells.

• Water soluble hormones: Water-soluble hormones include peptide and amino acid hormones such as insulin, epinephrine, HGH, and oxytocin. As their name suggests, these hormones are water soluble. Water-soluble hormones cannot pass through the phospholipid bilayer of the plasma membrane and therefore depend on receptor molecules on the cell surface. When a water-soluble hormone binds to a receptor molecule on the surface of a cell, it causes a reaction inside the cell. This reaction can change a factor inside the cell, such as the permeability of the membrane or the activation of another molecule. A common reaction is to cause molecules of cyclic adenosine monophosphate (cAMP) to be synthesized from adenosine triphosphate (ATP) present in the cell. cAMP acts as a second messenger inside the cell where it binds to a second receptor to alter the function of the cell's physiology.
• Lipid soluble hormones: Fat-soluble hormones include steroid hormones such as testosterone, estrogen, glucocorticoids, and mineralocorticoids. Because they are lipid soluble, these hormones are able to pass directly through the phospholipid bilayer of the plasma membrane and bind directly to receptors within the cell nucleus. Lipid-soluble hormones are able to directly control the function of a cell from these receptors, often causing specific genes to be transcribed into DNA to produce "messenger RNAs (mRNAs)" that are used to make proteins that affect its growth and function. cell.