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in humans and other vertebrates, endocrine cells that elaborate adrenaline, noradrenaline, and probably a number of other catecholamines contained in their cytoplasmic granules; the cells secrete these substances into the blood. Chromaffin cells are derived from neural ectoderm. After fixation with chromium salts, the cells acquire a dark-brown color, hence the name “chromaffin.” The aggregate of chromaffin cells in the body make up the adrenal system.
In humans and other higher vertebrates the cells are polygonal or irregular, sometimes having barely perceptible appendages that are entwined with the capillaries and form aggregates— paraganglia—in various parts of the body (near the nerve ganglia and fibers, in the region of the cervicothoracic vessels, and in the parenchyma of organs). The largest aggregate of chromaffin cells is the adrenal medulla. The elaboration and discharge of neurohormones from the cytoplasmic granules into the blood are regulated by neuromechanisms. In lower vertebrates the chromaffin cells have many appendages and are diffused in the walls of the large arteries of the trunk and deep within the cardiac muscle; discharge of hormones from the cytoplasmic granules is continuous. Chromaffin cells have also been discovered in invertebrates, for example, in the ganglia of the ventral nerve cord in annelid worms.
REFERENCESSee references under PARAGANGLIA.
N. A. SMITTEN