. The chordates. Chordata. 218 Basic Structure of Vertebrates HEP. PORTAL BILE DUCT HEPATIC A R. SUPRARENAL VES. R. RENAL VES VENA CAVA LEFT SUPRARENAL GLAND. SUP MESENTERIC A, SPERMATIC COVARIAN) VES l"\V~;~\'- URETER MESENTERIC A. Fig. 185. The adrenals or suprarenals shown in relation to the kidneys as seen when the fat which normally encloses them is removed. The relations of the blood- vessels which supply them are shown. (A.) Artery; (L.) left; (R.) right; (V.) vein. (Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) The endocrine secreted
. The chordates. Chordata. 218 Basic Structure of Vertebrates HEP. PORTAL BILE DUCT HEPATIC A R. SUPRARENAL VES. R. RENAL VES VENA CAVA LEFT SUPRARENAL GLAND. SUP MESENTERIC A, SPERMATIC COVARIAN) VES l"\V~;~\'- URETER MESENTERIC A. Fig. 185. The adrenals or suprarenals shown in relation to the kidneys as seen when the fat which normally encloses them is removed. The relations of the blood- vessels which supply them are shown. (A.) Artery; (L.) left; (R.) right; (V.) vein. (Courtesy, Neal and Rand: "Chordate Anatomy," Philadelphia, The Blakiston Company.) The endocrine secreted by the medullary tissue of the adrenal is epinephrine or adrenalin, its empiric chemical formula being C9H13O3N. Like the sympathetic nerves, epinephrine has a stimulating effect upon smooth muscle. It is so potent that its physiologic effects appear even when it is diluted to 1 part in 400,000,000 of blood. The well-known experiments of W. B. Cannon led him to his emer- gency theory of adrenal action. He found that in a quiet, undisturbed animal epinephrine is absent from the blood. When, however, the animal is excited by pain, fear, or anger, epinephrine increases. As a result, the heart beats more strongly, breathing becomes deeper and more rapid, intestinal action ceases, the liver releases sugar more rapidly, the muscles respond more quickly to stimulation, the tonus of the blood-vessels is raised, the coagulability of the blood increases, and so the animal is prepared either to run or fight. Thus the medullary secretion reinforces the action of the sympathetic nerves. Cannon has shown also that a substance which resembles epi- nephrine is given off at the junction of a sympathetic nerve with its effector. This substance has been called "; The adrenal gland has characteristic visceral innervation, being entered by nerves from both the sympathetic and the parasympathetic autonomic divisions. The medulla serves as an amplifier for the tho- racolumbar divi
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