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Concept
Adrenal medulla
Summary
The adrenal medulla (medulla glandulae suprarenalis) is part of the adrenal gland. It is located at the center of the gland, being surrounded by the adrenal cortex. It is the innermost part of the adrenal gland, consisting of chromaffin cells that secrete catecholamines, including epinephrine (adrenaline), norepinephrine (noradrenaline), and a small amount of dopamine, in response to stimulation by sympathetic preganglionic neurons.
The adrenal medulla consists of irregularly shaped cells grouped around blood vessels. These cells are intimately connected with the sympathetic division of the autonomic nervous system (ANS). These adrenal medullary cells are modified postganglionic neurons, and preganglionic autonomic nerve fibers lead to them directly from the central nervous system. The adrenal medulla affects energy availability, heart rate, and basal metabolic rate. Recent research indicates that the adrenal medulla may receive input from higher-order cognitive centers in the prefrontal cortex as well as the sensory and motor cortices, providing credence to the idea that there are psychosomatic illnesses.
Chromaffin cells are derived from the embryonic neural crest, and are modified postganglionic sympathetic neurons. They are modified postganglionic sympathetic neurons of the autonomic nervous system that have lost their axons and dendrites, receiving innervation from corresponding preganglionic fibers. The cells form clusters around fenestrated capillaries where they release norepinephrine and epinephrine into the blood.
As a cluster of neuron cell bodies, the adrenal medulla is considered a modified ganglion of the sympathetic nervous system.
Rather than releasing a neurotransmitter, the cells of the adrenal medulla secrete hormones.
The adrenal medulla is the principal site of the conversion of the amino acid tyrosine into the catecholamines; epinephrine, norepinephrine, and dopamine.
Because the ANS, specifically the sympathetic division, exerts direct control over the chromaffin cells, the hormone release can occur rather quickly.
Official source
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