ADRENAL GLANDS Also known as supra-renal glands, these are two small triangular endocrine glands situated one upon the upper end of each kidney. (See diagram of abdomen.)
Structure Each suprarenal gland has an enveloping layer of fibrous tissue. Within this the gland shows two distinct parts: an outer, firm, deep-yellow, cortical (see cortex) layer, and a central, soft, dark-brown, medullary (see medulla) portion. The cortical part consists of columns of cells running from the surface inwards, whilst in the medullary portion the cells are arranged irregularly and separated from one another by large capillary blood-vessels.
Functions Removal of the suprarenal glands in animals is speedily followed by great muscular prostration and death in a few days. In human beings, disease of the suprarenal glands usually causes Addison's disease, in which the chief symptoms are increasing weakness and bronzing of the skin. The medulla of the glands produces a substance - adrenaline - the effects of which closely resemble those brought about by activity of the sympathetic nervous system: dilated pupils, hair standing on end, quickening and strengthening of the heart-beat, immobilization of the gut, increased output of sugar from the liver into the blood-stream. Several hormones (called corticosteroids) are produced in the cortex of the gland and play a vital role in the metabolism of the body. Some (such as aldosterone) control the electrolyte balance of the body and help to maintain the blood pressure and blood volume. Others are concerned in carbohydrate metabolism, whilst others again are concerned with sex physiology, hydrocortisone is the most important hormone of the adrenal cortex, controlling as it does the body's use of carbohydrates, fats and proteins. It also helps to suppress inflammatory reactions and has an influence on the immune system