Final answer:
The chromaffin cells of the adrenal medulla express nicotinic cholinergic receptors, which are stimulated by acetylcholine released from preganglionic sympathetic fibers, leading to the release of catecholamines into the bloodstream.
Step-by-step explanation:
The neurosecretory chromaffin cells of the adrenal medulla express nicotinic cholinergic receptors. These neurosecretory cells release signaling molecules like epinephrine and norepinephrine into the bloodstream. Chromaffin cells, which develop from the neural crest along with the sympathetic ganglia, function as modified postganglionic sympathetic neurons. They are responsible for the release of catecholamines, specifically epinephrine (adrenaline) and norepinephrine (noradrenaline), into the bloodstream.
These hormones then bind to adrenergic receptors on target cells throughout the body. Preganglionic sympathetic fibers release acetylcholine (ACh), which then binds to the nicotinic receptors on chromaffin cells, triggering the release of catecholamines. It is important to note that these cells do not use axons for signaling but release their secretions directly into the systemic circulation, and hence, the secretions are classified as hormones.