The Adrenal Glands

Written by docteam Friday, 02 July 2010 19:38

The adrenal glands are small flattened bodies lying on the outer, upper extremity of each kidney. They consist of two distinct parts, the cortex and the medulla, each producing its own characteristic secretion.

The hormones produced by the medulla are epinephrine and norepinephrine. Stimuli causing the release of these substances include pain, cold, emotions, stress, hemorrhage, lack of oxygen, and low blood sugar. When secreted into the bloodstream, epinephrine causes marked changes in the circulatory system. The rate of heartbeat is quickened, blood pressure is increased, and sugar is released into the bloodstream from reserves in the liver.

The pupils dilate. Blood vessels of the skin, mucous membranes, and kidneys constrict, but other (coronary system, skeletal muscle ,and lungs) dilate. Digestion is inhibited. There is an increased flow of blood to the muscles. Muscle fatigue is delayed. Epinephrine has been termed the emergency hormone, since it brings into play the body processes on which self preservation depends. The effect of norepinephrine is limited to the constriction of blood vessels.

Only minute quantities of epinephrine are normally present in the blood, the increased output being controlled by nervous excitation. Under the influence of strong emotions, such as fear, anger, joy, or grief, epinephrine is secreted into the bloodstream in increased amounts, and the body is instantly made ready for the performance of unusual physical feats. When these physiologic effects are being produced continually as the result of persistent worry, they are undesirable.

Thomas Addison in 1855 was the first to point out that the secretions of the adrenal cortex are essential to life. He described a severe deficiency that is known as Addisons's disease. The symptoms include extreme weakness, a lowered metabolic rate, low blood pressure, severe prostration, great susceptibility to fatigue, infections, anesthetics and anoxia (lack of oxygen), and a bronzelike pigmentation of the skin.