|Lay Jr, Donald|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 9/3/2004
Publication Date: N/A
Technical Abstract: Epinephrine is classified as a catecholamine and acts as both a neurotransmitter and a neurohormone. Upon stimulation of the sympathetic nervous system, epinephrine is synthesized and released from a small number of nerve cells in the central nervous system and a much larger number of cells in the medulla of the adrenal gland which release epinephrine into the vascular circulation. Activation of sympathetic neurons in the adrenal medulla causes the release of acetylcholine from nerves which terminate on chromaffin cells in the adrenal medulla. Receptor activation causes chromaffin cells to produce and release epinephrine and some norepinephrine into the blood. Epinephrine acts as an agonist for the adrenergic receptors alpha 1, alpha 2, ß1, and ß2. However the potency by which epinephrine can activate a receptor is less for ß receptors compared to alpha receptors. Once epinephrine is released into the blood it can reach and affect all tissues which possess adrenergic receptors. Epinephrine causes a multitude of effects which are both tissue and receptor specific. Through the circulation in the blood, epinephrine can cause sympathetic effects at tissues which receive little or no sympathetic innervation such as adipose tissue and blood cells. Almost all cells in the body have adrenergic receptors and thus the body is altered in a variety of ways when epinephrine is released into the circulation. Sympathetic activation occurs in response to stimuli such as fear, pain, anxiety, and stress. In response to these stimuli epinephrine causes: increased heart rate, increased stroke volume, relaxes vascular smooth muscle to increase blood flow to muscle, constricts vascular smooth muscle to decrease blood flow to the skin and intestine, mobilizes glucose from liver and fatty acids from adipose tissue, and stimulates the conversion of glycogen to glucose in the liver.