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The Endocrine System

Updated on March 14, 2021

What does the Endocrine System exactly do to the body?

The Endocrine glands which are the main organs in the endocrine system release hormones in the blood then distribute them to different parts of the body. These hormones are responsible for reproduction, metabolism, our body's physical growth, and mood changes,

Hormones and Glands

Think of the different glands in your body whose primary function is to release hormones into the bloodstream to be used by the body for its proper function.

What are Hormones?

Hormones are chemical substances produced by a gland that convey a message from one cell to another cell.

What is a Gland?

A gland is a body organ that produces certain hormones.

The Endocrine System is composed of several glands that produce substances we call hormones.

The study of the Endocrine System and of the diseases of the body organs that make up the endocrine system is called Endocrinology.


A. Endocrine glands located in the head and neck

Shown above are the glands found in the head and neck and the hormones they release:

The organs include the Hypothalamus, the Pineal Body, the Pituitary Glands (the Anterior Pituitary, the Posterior Pituitary Lobe), and the Thyroid glands.

1. The Hypothalamus produces these hormones:

a. Dopamine inhibits the release of prolactin from the anterior pituitary.

b. Oxytocin stimulates lactation (letdown reflex) and uterine contraction

c. Vasopressin, an antidiuretic hormone increases blood volume and promotes the reabsorption of water in the distal convoluted tubule and collecting duct of nephrons by increasing water permeability.

d. Somatostatin inhibits the release of both the growth hormone and the thyroid-stimulating hormone from the anterior pituitary

e. The Thyrotropin-releasing hormone (TRH) stimulates the release of thyroid-stimulating hormones from the anterior pituitary.

f. The Growth hormone-releasing hormone stimulates the release of growth hormones from the anterior pituitary.

g. The Gonadotropin-releasing hormone stimulates the release of both the follicle-stimulating hormone and the luteinizing hormone from the anterior pituitary

h. The Corticotropin-releasing hormone stimulates the release of the adenocorticotropic hormone from the anterior pituitary.

2. The Pineal Body secretes the hormone melatonin which is considered an antioxidant. Melatonin keeps track of our circadian rhythm including the sleep cycle.

3. The Pituitary Glands: The Anterior Pituitary Lobe and The Posterior Pituitary Lobe

The Anterior Pituitary Lobe produces these hormones:

1. The Growth hormone, as the name suggests, stimulates human growth and the reproduction of body cells. It also stimulates the release of the insulin-like growth factor 1 from the liver.

2. The Thyroid-stimulating hormone stimulates the production of thyroxine and triiodothyronine or T4 and T3 cells from the thyroid glands. It also stimulates the absorption of iodine by the thyroid glands.

3. The Adrenocorticotropic hormone stimulates the production and release of corticosteroid and androgen from the adrenocortical cells.

4. The Beta-endorphin inhibits the idea of pain.

5. The Follicle-stimulating hormone stimulates the production of sperms, and the production of androgen-binding protein from the testes. It also causes the seminiferous tubules in the males and the ovarian follicles in the females to mature.

6. The Luteinizing hormone stimulates the process of ovulation and the development of the corpus luteum in females. It stimulates the production of testosterone from the Leydig cells or interstitial cells in the males.

7. The Prolactin stimulates the production of of milk and its release from the mammary glands.

8. The Melanocyte-stimulating hormone stimulates the production of melanin and its release from the melanocyctes of the hair and skin.

The Posterior Pituitary Lobe releases these hormones

1. Oxytocin stimulates uterine contraction and lactation.

2. Vasopressin, an antidiuretic hormone increases blood volume and promotes the reabsorption of water in the distal convoluted tubule and collecting duct of the nephrons by increasing water permeability.

The Thyroid produces these hormones:

1. Triiodothyronine or T3 cells, promotes the production of proteins by by stimulating RNA polymerase I and II synthesis.

2. Thyroxine or T4 cells increase the body's basal metabolic rate by stimulating the body's use of energy and oxygen.

3. Calcitonin promotes the growth and development of bones by stimulating the production of osteoblasts. It also reduces calcium ion content in the blood by inhibiting the release of these minerals from the parafollicular cells.

B. Endocrine glands found in the alimentary system

Shown above are organs of the alimentary system and the hormones they release.

The organs include the Stomach, the Duodenum, the Liver, the Pancreas, the Kidney, and Adrenal glands and release the following hormones:

1. The stomach produces these hormones:

a. Gastrin stimulates the secretion of gastric acid.

b. Ghrelin stimulates the secretion of the growth hormones from the pituitary glands . It also stimulates appetite.

c. Neuropeptide Y stimulates a person's appetite and prevents him from engaging in physical activity. This hormone can be related to obesity due to its ability to make people eat more and exercise less.

d. Somostatin prevents the release of the hormones motilin, secretin, cholecystokinin, gastrin, glucagon, vasoactive intestinal peptide and gastric inhibitory polypeptide.

It slows down the removal of gastric substances from the stomach, aids in the contraction of the smooth muscles, and reduces the flow of blood inside the intestines.

e. Histamine stimulates the secretion of gastric acid in the stomach.

f. Endothelin stimulates the contraction of the smooth muscles in the stomach.

2. The Duodenum produces these hormones:

a. Secretin stimulates the release of the substance bicarbonate from the liver, pancreas and Brunner's glands. Itmakes the action of cholecystokinin more effective in the body and prevents gastric juice production.

b. Cholecystokinin stimulates the release of digestive enzymes from the pancreas. It also stimulates the release of bile from the gallbladder. It also suppresses hunger making this hormone closely associated with weight loss.

3. The Liver produces these hormones:

a. Insulin-like growth factor, also called Somatomedin regulates the growth of body cells and their development. Its used in the body is similar to that of insulin.

b. Angiotensinogen and angiotensin stimulates vasoconstriction and the release of the hormones aldosterone and adrenal cortex dipsogen.

c. Thrombopoietin stimulates the release of megakaryocyctes to produce platelets.

4. The Pancreas produces these hormones:

a. Insulin stimulates the release of glucose from the blood. It stimulates the process of glucogenesis and glycolysis in the liver and muscles. It aids in the absorption of lipids and the production of triglycerides in the adipocyctes. It also posesses other important anabolic properties.

b. Glucagon is important in the process of gluconogenesis and glycogenolysis in the liver. It also increases blood glucose level.

c. Somatostatin prevents the release of glucagon and insulin from the body.

d. Pancreatic polypeptide regulates the secretion function of the pancreas and regulates the level of glycogen in the liver.

5. The kidney produces these hormones

a. Renin is responsible for activating the renin-angiostenin system.

b. Erythropoietin stimulates the production of erythrocyctes

c. Calcitriol stimulates the absorption of phosphates and calcium from the gastrointestinal tract. It also inhibits the release of PTH or parathyroid hormones from the kidneys.

6. The adrenal glands produce these hormones

From the Adrenal Cortex:

Glucocorticoids stimulate and initiate the process of gluconeogenesis and the breakdown of fats in the adipose tissues. They inhibit the accumulation of glucose in the muscles and in the adipose tissues, inhibit inflammation (it is anti-inflammatory) and inhibit responses by the immune system (it is immunosuppressive).

Mineralocorticoids stimulate and initiate the reabsorption of sodium in the kidneys and the reabsorption of passive water in the kidneys resulting to high blood volume and high blood pressure.

They also stimulate potassium and hydrogen secretion into the nephrons and its final excretion in the kidneys.

From the Adrenal Medulla

Adrenaline produces what we call the flight-or-fight response by

C. The Reproductive glands

The organs include the Testes, the Ovarian Follicles, the Placenta and Uterus

From the testes:

Testosterone is responsible for the development of muscle mass and muscle strength, bone growth and strength and increase in bone density.

It is responsible for the development of the male scrotum, for making the male voice deep, the growth of beard and other body hair and for making the sex organs mature.

Estradiol prevents the sudden death of germ cells.

Inhibin prevents the production of the follicle-stimulating hormones.

From the Ovarian follicle and corpus luteum:

Progesterone is very important in pregnancy. It is responsible for converting the endometrium to secretory stage, for thickening the cervical mucus and making it free of sperms.

Androstenedione is responsible for the development of female secondary sex traits. It speeds up a person's body metabolism and growth in height. It decreases muscle mass and bone resorption.

Estrogens mainly Estradiol is important in fluid balance, regulating gastrointestinal tract activity, melanin production, cancer prevention and lung function.

Inhibin prevents the production of FSH from the anterior pituitary glands.

From the placenta when pregnant:

Progesterone supports pregnancy by inhibiting the early onset of labor and inhibiting lactation.

Estrogens mainly Estriol

Human chorionic gonadotropin maintains the health of corpus luteum from the beginning of pregnancy.

From the uterus when pregnant:

Prolactin stimulates the release of milk from the mammary glands

Relaxin is not clearly defined both in animals and humans.

D. Endocrine organs to regulate the production of calcium

The organs include the Skin and Parathyroid glands

E. Others

These organs include the Heart, Bone Marrow and adipose tissues.

© 2012 Zee Mercado


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