The adrenal medulla produces adrenomedullary hormones in chromaffin cells, cells which are very similar in structure to post-synaptic sympathetic neurons, even though they are not neurons they are derivatives of the neural crest.
They then rapidly reach the anterior pituitary where they exert their hormonal action.
The residual hormones pass into the systemic circulation where they are diluted, degraded and have comparatively little effects.
[10] The synthesis, storage (in chromaffin cells) and release of catecholamines is co-regulated by synaptic input from their respective pre-synaptic sympathetic neurons, as well as hormonal and local inputs.
[11][12] The adrenomedullary hormones are: Enterochromaffin cells in the epithelia lining the lumen of the digestive tract secrete serotonin, while enterochromaffin-like cells at the stomach glands secrete histamine.