Adrenal Medulla
The inner region of the adrenal gland, the adrenal medulla, is a mod- ified sympathetic ganglion of the autonomic nervous system (ANS).The hormone-producing cells, called chromaffin cells (KRO- -maf-in; chrom- = color; -affin = affinity for; see Figure 18.14d), are innervated by sympathetic pregan- glionic neurons of the ANS.The two major hormones synthesized by the adrenal medulla are epinephrine (ep?-i-NEF-rin) and norepinephrine (NE), also called adren- aline and noradrenaline, respectively.Control of Secretion of Epinephrine and
Norepinephrine In stressful situations and during exercise, impulses from the hypothalamus stimulate sympathetic preganglionic neurons, which in turn stimulate the chromaffin cells to secrete epinephrine and norepinephrine.The chromaffin cells of the adrenal medulla secrete an unequal amount of these hormones--about 80% epi- nephrine and 20% norepinephrine.