mt training: endocrine

The adrenal gland, also called the suprarenal glands, are two small glands situated one on top of each kidney. Each gland consists of two parts, an outer portion called the adrenal cortex and an inner portion called the adrenal medulla.

The cortex secretes hormones called corticosteriods, and the medulla secretes hormones called catecholamines.

The adrenal cortex secretes three types of hormones known as corticosteriods.

i. Mineralocorticoids — These hormones regulate the amounts of mineral salt (also called electrolytes) that are retained in the body. A proper balance of water and salts and tissues is essential to the normal functioning of the body.

The most important mineralocorticoid hormone is called aldosterone. It increases the reabsorption into the bloodstream of sodium (a mineral electrolyte commonly found in salts) by the kidney tubules. At the same time, aldosterone stimulates the excretion of another electrolyte called potassium. The secretion of aldosterone increase manifold in the face of a severe sodium restricted diet, thereby enabling the body to hold needed salt in the bloodstream.

ii. Glucocorticoids — These steroid hormones have an important influence on the metabolism of sugars, fats and proteins within all body cells and have powerful anti-inflammatory effects.

Cortisol (also called hydrocortisone) is the most important (gluconeogenisis) and regulates the quantity of sugars, fats and of proteins in the blood and cells.

iii. Androgens, Estrogens and Progestins — These are male and female hormones that maintain the secondary sex characteristics, such as beard and breast development. And are necessary for reproduction. These hormones are also produced in the ovaries and testes. Excess adrenal androgen secretion in females leads to virilism --- (development of male characteristics), and excess adrenal estrogen and progestin secretion in males produces feminization (development of feminine characteristics).

The adrenal medulla secretes two types of catecholamine hormones.

i. Epinephrine (adrenaline) ---- This hormone increase cardiac rate, dilates bronchial tubes. And stimulates the production of glucose from a storage substance called glycogen when glucose is needed by the body.

ii. Norepinephrine (noradrenaline) --- This hormone constricts vessels and raises blood pressure.

Both epinephrine and norepinephrine are called sympathomimetic agents because they mimic, or copy, the actions of the sympathetic nervous system. During times of stress, these hormones are secreted by the adrenal medulla in response to nervous stimulation. They help the body respond to crisis situations by raising blood pressure, increasing heartbeat and respiration, and bringing sugar out of storage in the cells.

4. Pancreas

The pancreas is located behind the stomach in the region of the first and second lumbar vertebrae. It is both an exocrine and an endocrine gland.

The Exocrine part of pancreas secrete digestive enzymes and juices into the gastrointestinal tract.

The Endocrine part of pancreas consists of specialized cells that produce hormones called the islets of Langerhans (islet cells of the pancreas).

The islets of Langerhans (Endocrine part) produce two hormones,

v Insulin (produced by beta cells)

v Glucagons (produced by alpha cells).

Both of these hormones play a role in the proper metabolism of sugars and starches in the body. Insulin is necessary in the bloodstream so that sugars can pass from the blood into the blood cells of the body where they are burned to release energy. When blood sugar (glucose) is above normal level, insulin is released by the islet cells of the pancreas. The insulin causes glucose to enter body cells to be used for energy and stimulates the conversion of glucose to glycogen (a starch-storage form of sugar) in liver. Thus, sugar can leave the blood to be stored (as glycogen) or used to release energy. Glucagons, the opposite ‘twin’ of insulin, is released into the blood when sugar levels are below normal. It causes the breakdown of stored liver glycogen, to glucose, so that there is a rise in the sugar content of blood leaving the liver.

5. Pituitary Gland

The pituitary gland, also called the hypophysis, is a small, pea-sized gland located at the base of the brain in a small, pocket — like depression of the skull called the sella turcica. It is a well-protected gland with the entire mass of the brain above it and the nasal cavity below.

The pituitary consists of two distinct parts:

v An anterior lobe called the adenohypophysis glandular in nature; and a

v Posterior lobe called the neurohypopsis, composed of nervous tissue.

The hypothalamus is a region of the brain that is in close proximity to the pituitary gland. Signals transmitted from the hypophysis is controlled by nerve fibres originating in the hypothalamus and ending in the neurohypophysis. Secretion by the adenohypophysis is controlled by special hormones called releasing and inhibiting factors. These hormones are secreted by the hypothalamus and pass to the adenohypophysis by way of special capillaries.