Structure and functions of Adrenal gland Each adrenal

Structure and functions of Adrenal gland

• Each adrenal or suprarenal gland in man weight about 6 grams, measures 25 to 50 mm in length, and lies at the top of each kidney. • The adrenal glands are somewhat pyramidal in shape and have a rich blood supply. • They are innervated by the sympathetic nervous system, and consist of two parts that are embryologically, anatomically and functionally different. • In the typical mammal, each gland consists of an external reddish brown cortex which surrounds an internal grayish medulla.

• The cortex is made up of three zones, the cells of which differ in form and function. • The outermost zona glomerulosa (ZG) • The thick, middle zona fasciculata (ZF) • The third or the innermost zone is the zona reticularis (ZR)

• Hormones of the Adrenal Cortex • The adrenal cortex is absolutely essential to life. When it is completely removed most animals will not live more than a week or so. • The cortex has several hormones and it ranks next to the adenohypophysis in endocrine importance. • Secretion of the cortical hormones is under the control of ACTH from the pituitary. • All the adrenocortical hormones are steroid compounds and can be divided into three groups.

• Glucocorticoids such as cortisone, hydrocortisone (cortisol), and corticosterone. • (ii) Mineralocorticoids such as aldosterone and deoxycorticosterone. • (iii)Androgens sex hormones which have chiefly androgenic and to minor extent estrogenic effects.

• Functions of the Adrenocortical Hormones: • 1. Effect on carbohydrate and protein metabolism: • The glucocorticoid hormones exert their influence primarily on carbohydrate metabolism. • They increase the blood glucose level. Enhance the conversion of protein (and fat) to carbohydrates. • Cortisol also affects fat metabolism.

• 2. Effect on mineral, salt, and water Metabolism: The mineral corticoids have a regulatory effect on the relative concentrations of mineral ions (especially sodium and potassium) in the body fluids, and therefore on the water contents of the tissues. • The insufficiency of the mineral corticoids results in an increased excretion into the urine of sodium ions, chloride ions, and water, accompanied by a fall in blood sodium chloride, and bicarbonate. • The administration of the mineral corticoid hormones has the opposite effects, resulting in an increase in blood sodium and chloride concentrations, more retention of water by the body, a decrease in potassium concentration, and a restoration of p. H of the blood to its more normally alkaline level. •

• 3. Effect on sexual development: • Under certain circumstances the adrenal cortex appears to secrete steroids which are similar in their effects to male hormones. • For example, adrenal cortical tumours in females may give rise to masculine characters, such as beard and deep voice, etc. • Although the female sex hormones have also been detected in cortical extract, it is believed that they are simply intermediates in the formation of other adrenocorticosterioids.

• 4. Anti-allergy, anti-inflammatory and other effects: • Several of the cortical hormones (e. g. , cortisol and cortisone) have a marked influence in preventing the appearance of an inflammation. • They are also used to control the symptoms of particular arthritic conditions and rheumatic fever. • The steroid secretions of the adrenal cortex also exercise several other influences on the body functions including a role in decreasing the level or red and white blood cells and stimulating the secretions of the digestive tract.

• Hypoadrenalism : • Insufficiency of the cortical hormones results in Addison’s disease. • In this disease the adrenal cortex degenerates, resulting in a number of symptoms, including a characteristic bronzing of the skin, muscular weakness, low blood pressure, and digestive disturbance. • The sufferers of this disease are cured by a proper administration of cortical hormones from some external source.

• Hyperadrenalism : • Hyperfunction or over secretion by the adrenal cortex as a result of excessive secretion of ACTH, gives rise to Cushing’s disease. • The symptoms include high blood pressure, salt retention, swelling of the tissues with water, demineralization of the bones, and loss of sexual function. • . Treatment in Cushing’s disease consists of removing an adrenal tumor if this is the cause, or decreasing the secretion of ACTH. if possible.

• Hormones of the Adrenal Medulla: • The adrenal medulla in man consists of two distinct types of cells. • These are adrenaline-secreting cells and the noradrenaline-secreting cells which are responsible for the production of the two hormones, adrenaline or epinephrine and norepinephrine or noradrenaline respectively.

• Adrenaline functions as the so-called “emergency” hormone for the body because the general secretion of this hormone centers around emergency functions of the body such as those of fear, fight, and anger, etc. • During emotional states epinephrine (adrenaline) is secreted in great amounts. It has a decided effect in elevating the glucose level in the bloodstream by somehow enhancing enzymatic conversion of liver glycogen to glucose. • The rise in blood glucose is accompanied by an increase in oxygen consumption, body temperature and heat production.

• Together, most or all these effects are sometimes called the alarm reaction. • If the action of adrenaline is somehow inhibited, a vertebrate cannot adjust rapidly to emergencies. • Noradrenaline (Norepinephrine): • This hormone of the adrenal medulla has somewhat similar effects. • It raises the blood pressure, but it is responsible for constriction instead of dilation of the blood vessels. • Noradrenaline is a chemical transmitter at sympathetic nerve endings and in the central nervous system, but is also present in the adrenal medulla, both as a hormone and also as precursor of adrenaline.