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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.

Adrenal Medulla
The inner region of the adrenal gland, the adrenal medulla, is a mod- ified sympathetic ganglion of the autonomic nervous system (ANS). It develops from the same embryonic tissue as all other sympathetic ganglia, but its cells, which lack axons, form clusters around large blood vessels. Rather than releasing a neurotransmitter, the cells of the adrenal medulla secrete hormones. 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. Because the ANS exerts direct control over the chromaffin cells, hormone release can occur very quickly.
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. The chromaffin cells of the adrenal medulla secrete an unequal amount of these hormones—about 80% epi- nephrine and 20% norepinephrine. The hormones of the adrenal medulla intensify sympathetic responses that occur in other parts of the body.
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. These two hormones greatly augment the fight-or-flight response that you learned about in Chapter 15. By increasing heart rate and force of contraction, epinephrine and norepinephrine increase the output of the heart, which increases blood pressure. They also increase blood flow to the heart, liver, skeletal muscles, and adipose tissue; dilate airways to the lungs; and increase blood levels of glucose and fatty acids.