Gastrointestinal function is regulated by a set of neural signaling molecules (neurotransmitters and neuropeptides) whose physiological effect is determined jointly by their source division of the nervous system — parasympathetic, sympathetic, enteric, or sensory afferent — and by their target effector: smooth muscle motility, glandular secretion, sphincter tone, or mucosal blood flow. The organizing principle is that parasympathetic and afferent transmitters are broadly excitatory or vasodilatory (increasing motility, secretion, and perfusion), while sympathetic transmitters are broadly inhibitory or vasoconstrictive, with the enteric nervous system providing local control such as sphincteric constriction that gates transit between GI compartments. This topic belongs to gastrointestinal physiology within systems physiology and neurophysiology, and it grounds the wider discipline's account of autonomic and enteric (the "second brain") regulation of digestion.
Gastrointestinal function is regulated by a set of neural signaling molecules (neurotransmitters and neuropeptides) whose physiological effect is determined jointly by their source division of the ne…