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| Chromaffin cell ： ウィキペディア英語版 |
Chromaffin cell
Chromaffin cells, also pheochromocytes, are neuroendocrine cells found mostly in the medulla of the adrenal glands (located above the kidneys) in mammals. They are in close proximity to pre-synaptic sympathetic ganglia of the sympathetic nervous system, with which they communicate, and structurally they are similar to post-synaptic sympathetic neurons. In order to activate chromaffin cells, the splanchnic nerve of the sympathetic nervous system releases acetylcholine, which then binds to nicotinic acetylcholine receptors on the adrenal medulla. This causes release of catecholamines. The chomaffin cells release catecholamines: ~80% of Epinephrine (Adrenaline) and ~20% of Norepinephrine (Noradrenaline) into systemic circulation for systemic effects on multiple organs (similarly to secretory neurons of the hypothalamus), and can also send paracrine signals. Hence they are called neuroendocrine cells.
In the mammalian fetal development (fourth to fifth week in humans), neuroblast cells migrate from the neural crest to form the sympathetic chain and preaortic ganglia. The cells migrate a second time to the adrenal medulla. Chromaffin cells also settle near the sympathetic ganglia, vagus nerve, paraganglia, and carotid arteries. The largest extra-adrenal cluster of chromaffin cells in mammals is the organ of Zuckerkandl. In lower concentrations, extra-adrenal chromaffin cells also reside in the bladder wall, prostate, and behind the liver.
In non-mammals, chromaffin cells are found in a variety of places, generally not organized as an individual organ, and may be without innervation, relying only on endocrine or paracrine signals for secretion.
==Function==
Chromaffin cells of the adrenal medulla are innervated by the splanchnic nerve and secrete adrenaline (epinephrine), noradrenaline (norepinephrine), a little dopamine, enkephalin and enkephalin-containing peptides, and a few other hormones into the blood stream. The secreted adrenaline and noradrenaline play an important role in the fight-or-flight response. The enkephalins and enkephalin-containing peptides are related to, but distinct from endogenous peptides named endorphins (which are secreted from the pituitary); all of these peptides bind to opioid receptors and produce analgesic (and other) responses. The hormones are secreted from chromaffin granules; this is where the enzyme dopamine β-hydroxylase catalyzes the conversion of dopamine to noradrenaline. Distinct N and E cell forms exist (also Na and A cells in British nomenclature - noradrenaline and adrenaline); the former produce norepinephrine, the latter arise out of N cells through interaction with glucocorticoids, and convert norepinephrine into epinephrine.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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