Glands of the Endocrine System

Summary of the locations of the main endocrine glands in the human body and the hormones secreted by them:

Locations of the main Endocrine Glands:

Hormones secreted by these Endocrine Glands:

1. Hypothalamus

The hypothalamus is the part of the brain sometimes described as the 'control centre' or 'control and relay centre' because it is the region of the brain that regulates the interaction of the endocrine system and the nervous system. The hypothalamus contains centres that control body temperature, hunger and hence eating, and water balance and hence thirst. It produces two hormones, ADH and oxytocin. As they are secreted from the posterior pituitary they are listed in 2. below.

2. Pituitary Gland and Pineal Gland

The pituitary gland hangs from the hypothalamus by a short stalk-like structure. Located at the base of the skull, it is protected by a depression in the sphenoid bone called the pituitary fossa (also known as the sella turcica). The pituitary gland is sometimes called the 'master gland' of the human endocrine system because it secrets some hormones that control other endocrine glands by stimulating them to release specific hormones. However, the master of the pituitary gland is the hypothalamus.

The pituitary gland consists of 3 lobes, the posterior lobe, the anterior lobe and the interior (or 'intermediate') lobe.

Hormone(s) Secreted

Function(s) of Hormones

From the Posterior Lobe:

Oxytocin

  • Stimulates utrine contraction and brest contraction for milk release.

Anti-Diuretic Hormone (ADH), also known as "vasopressin"

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

From the Anterior Lobe:

Prolactin (PRL)

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

Human Growth Hormone (HGH)

  • Growth
  • Hypo- Dwarfism
  • Hyper- Gigantism

Thyroid Stimulating Hormone (TSH)

  • Stimulates the thyroid to release thyroxin.

Adrenocorticotrophic Hormone (ACTH)

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

Luteinizing Hormone (LH)

  • Brings about ovulation and maintains the corpus luteum.

Follicle Stimulating Hormone (FSH)

  • 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)

 

Gonadotrophins

  • Secondary sexual characteristics

Interstitial Cell Stimulating Hormone (ICSH)

  • 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.)

From the Intermediate Lobe:

Intermedin

  • Control of melanocyte production.

Pineal Gland

The pineal gland is 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.

Hormone(s) Secreted

Function(s) of Hormones

Melatonin

  • 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.

3. Thyroid and Parathyroid Glands

The thyroid gland, which is in the neck, consists of two connected lobes. Most people have four parathyroid glands located on the back of the thyroid gland. The thyroid and parathyroid glands share a similar blood supply and drainage, and lymphatic drainage.

Hormone(s) Secreted

Function(s) of Hormones

Thyroid Gland:

Thyroxin

  • 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 impaired, if occurs in children).

Calcitonin

  • Uptake of calcium to bone.

Parathyroid Gland:

Parathormone

  • 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 straddled across the trachea and bronchi in the upper thorax. In infancy the thymus controls the development of lymphoid tissue and the immune response to microbes and foreign proteins.

Hormone(s) Secreted

Function(s) of Hormones

Thymosin

  • 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 islets of Langerhans contain both Alpha- and Beta- cells.

Hormone(s) Secreted

Function(s) of Hormones

From the Beta Cells:

Insulin

  • 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, fat and protein are broken-down for energy. Coma and death may follow if the symptoms are not treated.

From the Alpha Cells:

Glucagon

  • Conversion of glycogen to glucose.

6. Adrenal Glands

The adrenal glands have two distinct parts, the adrenal cortex (outer-layer) and the adrenal medulla (center).

Hormone(s) Secreted

Function(s) of Hormones

From the Adrenal Medulla:

Adrenalin

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.

Noradrenalin

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.

From the Adrenal Cortex:

Corticosteroids

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

The ovaries (female only) produce mature ova.

Hormone(s) Secreted

Function(s) of Hormones

Oestrogen

  • Break-down of the utrine wall.

Progesterone

  • 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

The testes (male only) are located outside the pelvic cavity.

Hormone(s) Secreted

Function(s) of Hormones

Testosterone

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