ADRENAL GLANDS, two flattened, yellowish brown bodies, about tin. long which lie on the upper anterior surface of the kidneys, called also suprarenal glands. They have no ducts but pour their secretions directly into the blood stream, and are therefore called ductless or endocrine glands. Their function is closely related to that of the other ductless glands, such as the thyroid, pituitary, liver and gonads, in controlling the normal growth and development of the body and in maintaining a certain equilibrium among its various processes. Each ductless gland, besides having a special function, seems to have an effect on every other ductless gland, and these interrelated effects are so complex that it is difficult to isolate the activity of a single gland.
Removal of both adrenal glands in animals is followed by death in about 48 hours and destructive disease of these glands in man produces a symptom complex called Addison's disease, which is ultimately fatal. They therefore seem to perform some function necessary to life. Each gland consists of two distinct and origi nally separate layers, the yellowish cortex which covers the whole external surface and the gray central part, or medulla. The exact function of the cortex is unknown, but it seems to play a role in sexual development and to be the part necessary to life. The medulla, on the other hand appears in the embryo from a group of those nerve cells which migrate from the nerve layer to form ganglia or relay stations of the sympathetic nervous system. The cells of the medulla are presumed to secrete the chemical sub stance which has been isolated and analyzed from extracts of the whole gland.
This substance, called epinephrine or adrenalin, may be re garded, according to Cannon's theory, as an emergency messenger which supplements the activity of the sympathetic nervous sys tern in times of emotional stress. Under the influence of such emotions as fear and anger, the adrenals, stimulated by the sym pathetic nerves, mobilize the resources of the body for such exertions as struggle or flight. The actual effects of a sudden out pouring of epinephrine into the blood may be observed experi mentally and consist in an increase in the blood pressure and pulse rate, inhibition of digestion, erection of the hair, dilatation of the pupil and a rise in the blood sugar. (See DUCTLESS