The adrenal glands in humans are two glands that are situated on top of each kidney.
The adrenal gland is comprised anatomically from a capsule and a cortex and a medulla.
The cortex constitutes approximately 90% of the total weight of the gland.
The adrenal gland is supplied with blood from the superior renal artery.
The cortex is the site of steroids secretion, and in particular the hormone cortisol. The medulla of the adrenal gland secretes catecholamines, and in particular epinephrine and norepinephrine.
The cortex of the adrenal gland is divided into three areas or zones. These are the glomerular zone and the fasciculate zone and the reticular zone.
Aldosterone is a hormone that is secreted by the cortex of the adrenal gland, and in particular by the glomerular zone. Aldosterone secretion increases sodium reabsorption by the distal tubules of the kidney nephrons in exchange for potassium which is secreted.
A decreased blood pressure or low sodium levels stimulates a series of reactions that lead eventually to secretion of aldosterone which in turn acts by increasing sodium levels in the blood through its reabsorption along with water. Thus elevating blood pressure to normal values.
Angiotensin-converting enzyme or ACE catalyzes an important reaction in the aldosterone formation cascade which leads eventually to elevating the blood pressure.
Inhibitors of this enzyme are used clinically as drugs to lower the blood pressure of patients suffering from high blood pressure.
Another secretion of the cortex of the adrenal gland is glucocorticoid. It is secreted by the fasciculate zone. One important glucocorticoid is cortisol. Cortisol is used as an anti-inflammatory agent and as a suppressing agent for the immune system. Cortisol secretion is under the feedback of the adreno-corticotropic hormone or ACTH.
The cortex is also responsible for secreting androgens or male sex hormones, especially Dehydro-epiandrosterone or DHEA. These androgens are secreted by the reticular zone of the cortex of the adrenal gland.
A tumor of the adrenal cortex is manifested by excessive secretion of andregens. This condition has clinical symptoms in females as hair growth and restoration of menses in women with menopause or who had stopped menses.
The adrenal medulla secretes catecholamines and in particular epinephrine and norepinephrine. These two hormones prepare the body for stress situation such as increased blood pressure by constricting the blood vessels. In addition to increasing heart rate as well.
A tumor of the adrenal medulla which is called pheochromocytoma is manifested clinically as excessive secretion of epinephrine and norepinephrine by the medulla of the gland. The clinical symptoms of this condition are high blood pressure without an apparent reason.