considered as a specialized sympathetic ganglion. Unlike other sympathetic ganglia, however, the adrenal medulla lacks distinct synapses and releases its secretions directly into the blood. Blood supply The adrenal glands have one of the greatest blood supply rates per gram of tissue of any organ: up to 60 small arteries may enter each gland. Three arteries usually supply each adrenal gland: The superior suprarenal artery, a branch of the inferior phrenic artery The middle suprarenal artery, a direct branch of the abdominal aorta The inferior suprarenal artery, a branch of the renal artery These blood vessels supply a network of small arteries within the capsule of the adrenal glands. Thin strands of the capsule enter the glands, carrying blood to them. Venous blood is drained from the glands by the suprarenal veins, usually one for each gland: The right suprarenal vein drains into the inferior vena cava The left suprarenal vein drains into the left renal vein or the left inferior phrenic vein. The central adrenomedullary vein, in the adrenal medulla, is an unusual type of blood vessel. Its structure is different from the other veins in that the smooth muscle in its tunica media (the middle layer of the vessel) is arranged in conspicuous, longitudinally oriented bundles. Variability The adrenal glands may not develop at all, or may be fused in the midline behind the aorta. These are associated with other congenital abnormalities, such as failure of the kidneys to develop, or fused kidneys. The gland may develop with a partial or complete absence of the cortex, or may develop in an unusual location. Function The adrenal gland secretes a number of different hormones which are metabolised by enzymes either within the gland or in other parts of the body. These hormones are involved in a number of essential biological functions. Corticosteroids Corticosteroids are a group of steroid hormones produced from the cortex of the adrenal gland, from which they are named. Mineralocorticoids such as aldosterone regulate salt ("mineral") balance and blood pressure Glucocorticoids such as cortisol influence metabolism rates of proteins, fats and sugars ("glucose"). Androgens such as dehydroepiandrosterone. Mineralocorticoids The adrenal gland produces aldosterone, a mineralocorticoid, which is important in the regulation of salt ("mineral") balance and blood volume. In the kidneys, aldosterone acts on the distal convoluted tubules and the collecting ducts by increasing the reabsorption of sodium and the excretion of both potassium and hydrogen