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Glands of the Human Endocrine System

This page is a simple summary of the locations of the main endocrine glands in the human body, and the hormones secreted by these glands.

Locations in the body of the main Endocrine Glands:

 


Hormones secreted by the main Endocrine Glands:

Endocrine Gland

Hormone(s) Secreted

Function(s) of Hormones

(1) Hypothalamus

Part of the Brain: The Control and Relay Centre of the Endocrine System.

(2) Pituitary

Known as the "Master Gland", this part of the brain consists of three lobes called "anterior", "interior" and "posterior".

Posterior

  • Stimulates utrine contraction and brest contraction for milk release.

Posterior

  • Stimulates re-absorption of water from kidney tubules.
  • Hypo- causes Diabetes Insipidus
    (large amounts of urine produced).

Anterior

  • Production of breast milk (works in men too).

Anterior

  • Growth
  • Hypo- Dwarfism
  • Hyper- Gigantism

 

  • Stimulates the thyroid to release thyroxin.

Anterior

  • Stimulates the adrenal cortex to produce:
    Corticosteriods:
    • mineral corticoids
    • glucocorticoids
    • cortisol (natural anti-inflammatory)
    • androgens, e.g. acdosterone

Anterior

  • Brings about ovulation and maintains the corpus luteum.

Anterior

  • Stimulates growth/development of Graafin follicles (= a mature follicle in the ovary prior to ovulation, containing a large fluid-filled cavity that distends the surface of the ovary) on approx. 28 day cycle.

 

  • Melanin Stimulating Hormone (MSH)
 

 

  • Secondary sexual characteristics

Anterior

  • Works on the seminiferous tubules in the testes – to produce sperm – which take 21 days to mature. (If not ejaculated within 21 days, the sperm are re-absorbed back into the body.)

Intermediate

  • Control of melanocyte production.

(2) Pineal

A pea-sized mass of nerve tissue attached by a stalk to the posterior wall of the third ventricle of the brain, deep between the cerebral hemispheres at the back of the skull.
(It functions as a gland, secreting the hormone melatonin - which regulates the pituitary gland and is associated with the biological clock.)

 

  • A hormone produced by the pineal gland in darkness but not in bright light.
  • Melatonin receptors in the brain react to this hormone and synchronize the body to the 24 hour day/night rhythm, thus informing the brain when it is day and when it is night.
  • Melatonin is derived from seratonin, with which it works to regulate the sleep cycle.

(3a) Thyroid Gland

Part of the Thyroid/Parathyroid Gland, which is in the neck.

 

  • Concerned with the Basal Metabolic Rate (BMR), which is the amount of energy the body uses, just to ‘tick over’

Hyper-Thyroidism = ‘over-active thyroid’ = Thyrotoxicosis
Symptoms: increase in BMR; increase in heart-rate; loss of weight; hyper-activity; insomniac; develops bulging eyes due to accumulation of fluid behind the eye; may develop Goitre; possible link with Attention Deficit Disorder.

Hypo-Thyroidism
Symptoms; decrease in BMR; weight gain; lethargy; skin becomes dry and puffy; hair becomes thin and brittle.
Causes: Derbyshire Neck (originally due to insufficient iodine in the soil in Derbyshire), Graves Disease, and Cretinism (= metal and sexual development imapaired, if occurs in children).

 

  • Uptake of calcium to bone.

(3b) Parathyroid Gland

Part of the Thyroid/Parathyroid Gland, which is in the neck.

 

  • Associated with the growth of muscle and bone.
  • Distribution of calcium and phosphate in the body.

Hyper- Causes transfer of calcium from the bones to the blood; bones become fragile & easily broken; osteoporosis. (Parathormone activity is inhibited by oestrogen.)

Hypo- Lowers blood calcium levels, causing tetany (which may be treated by injections of the hormone); low calcium levels in skeletal muscle (which may cause cramps).

(4) Thymus

The thymus gland is located straddled across the trachea & bronchi in the upper thorax (a bi-lobed organ in the root of the neck, above and in front of the heart).
The thymus (a gland associated with the immune system), is enclosed in a capsule and divided internally by cross-walls into many lobules (full of T-lymphocytes). In relation to body size the thymus is largest at birth. It doubles in size by puberty, after which it gradually shrinks, its functional tissue being replaced by fatty tissue. In infancy the thymus controls the development of lymphoid tissue and the immune response to microbes and foreign proteins (accounting for allergic response, antoimmunity, and the rejection of organ transplants). T-lymphocytes migrate from the bone marrow to the thymus, where they mature and differentiate until activated by antigen.

 

  • Activates the immune system by activating the T-Cells (T-Killer Cells; T-Helper Cells; T-Memory Cells).

 

  • T-Lymphocytes
  • The thymus consists of lobules full of T-lymphocytes (white blood cells associated with antibody production).
  • T-lymphocytes migrate from the bone marrow to the thymus, where they mature and differentiate until activated by antigens.

(5) Pancreas

The pancreas lies behind the stomach.
It is both exocrine (ducted) and endocrine (ductless).

As an exocrine gland it secrets enzymes (organic catalysts) into the small intestine.

The enzymes are:

  • Pancreatic amylase (which breaks down polysaccharides, i.e. starch into sugar)
  • Lipase (which breaks down fats into fatty acids and glycerol)
  • Proteases (which breaks down protein (polypeptide) into di-peptides).

The islets of Langerhans are within the pancreas.

Islets of Langerhans

Located within the pancreas. Contains groups of both Alpha- and Beta- cells.

Beta Cells

  • Conversion of glucose to glycogen.
  • Cellular up-take of Glucose.
  • Conversion of excess glucose to fat.

Hyper-

Hypo- causes Diabetes Mellitus:

Symptoms: Blood glucose levels rise (hyperglycaemia). Glucose is excreted into the urine (glycosuria) - which increases levels of urination, causing dehydration.
As glucose levels in the blood increase, fa and protein are broken-down for energy. Coma and death may follow if the symptoms are not treated.

Alpha Cells

  • Conversion of glycogen to glucose.

(6) Adrenal Glands

Adrenal Medulla

Prepares the body for "fright, fight or flight" and has many effects:

  • Action of heart increased.
  • Rate and depth of breathing increased.
  • Metabolic rate increased.
  • Force of muscular contraction improves.
  • Onset of muscular fatigue delayed.
  • Blood supply to the bladder and intestines reduced, their muscular walls relax, the sphincters contract.

 

Similar effects to adrenalin:

  • Constriction of small blood vessels leading to increase in blood pressure.
  • Increased blood flow through the coronary arteries and slowing of heart rate.
  • Increase in rate and depth of breathing.
  • Relaxation of the smooth muscle in the intestinal walls.

Adrenal Cortex

Glucocorticoids (e.g. cortisol, cortisone, corticosterone)

  • Utilization of carbohydrate, fat and protein by the body.
  • Normal response to stress.
  • Anti-inflammatory effects.
  • Hypersecretion of cortisol results in Cushings Syndrom.

Mineralocorticoids (e.g. aldosterone)

  • Regulation of salt and water balance.
  • Hypersecretion of Alderosterone decreases the potassium in the body (affecting nerve impulse transmission and leading to muscular paralysis).

(7) Ovaries

Produce mature ova. Theoretical potential for 400-450 viable ova.
(Therefore the more and the longer pregnancies a woman has, the later her menopause because there is no ovulation during pregnancy.)

 

  • Break-down of the utrine wall.

 

  • Builds up and maintains the uterus wall for embedding of fertilized egg.
  • Associated with secondary sexual characteristics, e.g. body hair, breast enlargement, changes in physical body.

(8) Testes

Located outside the pelvic cavity.

 

  • Development and function of male sex organs.
  • Secondary sexual characteristics. e.g. body hair, muscle development, voice change.


See also information about other aspects of the Endocrine System, inc. Conditions that affect the Endocrine System and the Locations of and Hormones secreted by the main Endocrine Glands are included on other pages of this website.

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