A pair of adrenal glands are located at the anterior end of the kidneys, hence also called suprarenal glands. Anatomically the outer region is the cortex and the inner region is the medulla.
Histologically the adrenal cortex has three distinct zones, zona glomerulosa, zona fasciculata and zona reticularis. Zona glomerulosa an outer thin layer constitutes about 15% of adrenal cortex, and secretes mineralocorticoids.
Zona fasciculata, the middle widest layer constitutes about 75% of adrenal cortex and secretes glucocorticoids such as cortisol, corticosterone and trace amounts of adrenal androgen and oestrogen. Zona reticularis, an inner zone of adrenal cortex constitute about 10% of adrenal cortex and secretes the adrenal androgen, trace amount of oestrogen and glucocorticoids.
Adrenal medulla: It is the central part of adrenal gland and is composed of ovoid and columnar cells, which are found around the network of blood capillaries. Adrenalin (epinephrine) and nor adrenalin (nor epinephrine) are the two hormones secreted by the adrenal medulla. Both adrenalin and nor adrenalin are catecholamines.
Function of adrenal hormones: Glucocorticoids stimulate gluconeogenesis, lipolysis and proteolysis (the life saving avtivity). Cortisol is a glucocorticoid invloved in maintaining cardio vascular and kidney functions.
It produces anti-inflammatory reactions and suppresses the immune response. It stimulates the RBC production. It is also known as stress combat hormone. Mineralocorticoids regulates water and electrolyte balance of our body.
Aldosterone stimulates the reabsorption of sodium and water and eliminates potassium and phosphate ions through excretion,, thus it helps in maintainting electrolytes, osmotic pressure and blood pressure. Adrenal androgen plays a role in hair growth in the axial region, pubis and face during puberty.
The adrenal medulla secretes the hormones adrenalin and noradrenalin and are referred as “3F hormone” (fight, flight and fright hormone). Adrenalin increases liver glycogen breakdown into glucose and increases the release of fatty acids from fat cells.
During emergency it increases heart beat rate and blood pressure. It stimulates the smooth muscles of cutaneous and visceral arteries to decrease blood flow. It increases blood flow to the skeletal muscles therby increases the metabolic rate of skeletal muscles, cardiac muscles and nervous tissue.
