Adrenal medulla





The adrenal medulla is located at the center of the adrenal gland, being surrounded by the adrenal cortex.



It is the innermost part of the adrenal gland, consisting of chromaffin cells that secrete catecholamines.



The catecholamines include:  epinephrine, norepinephrine, and a small amount of dopamine, in response to stimulation by sympathetic preganglionic neurons.



The adrenal medulla cells grouped around blood vessels are intimately connected with the sympathetic division of the autonomic nervous system (ANS). 



Adrenal medullary cells are modified postganglionic neurons, and preganglionic autonomic nerve fibers lead to them directly from the central nervous system. 



The adrenal medulla therefore affects energy availability, heart rate, and basal metabolic rate. 



The adrenal medulla may receive input from higher-order cognitive centers in the prefrontal cortex as well as the sensory and motor cortices, suggesting the relationship to  psychosomatic illnesses.



Chromaffin cells are derived from the embryonic neural crest.



Chromaffin cells are modified postganglionic sympathetic neurons of the autonomic nervous system.



Chromaffin cells have lost their axons and dendrites, and receive innervation from corresponding preganglionic fibers. 



Chromaffin cells cluster around capillaries where they release norepinephrine and epinephrine into the blood.



The adrenal medulla is considered a modified ganglion of the sympathetic nervous system, and 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.



The adrenal medulla is the principal site of the conversion of the amino acid tyrosine into the catecholamines; epinephrine, norepinephrine, and dopamine.



The autonomic nervous system’s 


sympathetic division, directly  controls the chromaffin cells.



The hormone secretion from the adrenal medulla can occur quickly.



When confronted with stress, exercise, or imminent danger the adrenal medulla chromaffin cells release the catecholamines adrenaline and noradrenaline into the blood. 



The adrenal medulla released catecholamine hormones 


are composed of  about 85% epinephrine  and 15% noradrenaline.



Catecholamine release is stimulated by nerve impulses, and receptors for catecholamines are widely distributed throughout the body.



Catecholamine effects of adrenaline and noradrenaline include:  increased heart rate and blood pressure, blood vessel constriction in the skin and gastrointestinal tract, smooth muscle bronchiole and capillary dilation, increased metabolism, all of which are characteristic of the fight-or-flight response.



The most common catecholamine-secreting tumor of the adrenal medulla is the pheochromocytoma.



A neuroblastoma, is a neuroendocrine tumor of any neural crest tissue of the sympathetic nervous system.



A ganglioneuroma, is a tumor in the nerve cells of the peripheral nervous system.



The adrenal medulla may be poorly formed or absent in cases of an absent adrenal gland. 



In dopamine beta hydroxylase deficiency, the entire body cannot efficiently produce epinephrine and norepinephrine from dopamine,  resulting  in severe dysautonomia: results  in autonomous nervous system failure which requires epinephrine and norepinephrine as neurotransmitters.


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