Chapter: Modern Pharmacology with Clinical Applications: General Organization and Functions of the Nervous System

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The Adrenal Medulla

The cells of the adrenal medulla, called chromaffin cells, are homologous with sympathetic postganglionic neurons.

THE ADRENAL MEDULLA

The cells of the adrenal medulla, called chromaffin cells, are homologous with sympathetic postganglionic neu-rons. The adrenal medulla may in fact be considered a modified sympathetic ganglion. The adrenal medulla se-cretes two hormones. One is norepinephrine, which is also the primary neurotransmitter of sympathetic post-ganglionic neurons. The other medullary hormone is epinephrine.

General activation of the sympathetic system during stress, fear, or anxiety is accompanied by increased se-cretion of adrenal medullary hormones, which consist primarily of epinephrine in the human. The secretory activity of the adrenal medulla is regulated by the CNS.

Some blood-borne substances of endogenous origin, such as histamine, angiotensin, and bradykinin, can di-rectly stimulate the chromaffin cells to secrete epineph-rine and norepinephrine. A variety of exogenously ad-ministered drugs, such as cholinomimetic agents and caffeine, can directly stimulate the secretion of adrenal medullary hormones. The neuronally induced secretion of medullary hormones is antagonized by ganglionic blocking agents.

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