Autonomic innervation of the gastrointestinal tract operates on a principle of reciprocal antagonism: sympathetic outflow, arising from thoracic and lumbar segments of the spinal cord and relaying through prevertebral/abdominal ganglia, inhibits digestive activity — reducing secretion and motility, increasing sphincter constriction, and decreasing splanchnic blood flow — while parasympathetic outflow does the converse. Vascular tone in the GI circulation is set by neurotransmitter identity rather than by nerve division alone: acetylcholine and vasoactive intestinal peptide (VIP) produce vasodilation by increasing vessel luminal diameter, whereas norepinephrine and ATP produce vasoconstriction by decreasing it, with calcitonin gene-related peptide (CGRP) and substance P from sensory neurons contributing a smaller dilatory component. This material belongs to gastrointestinal physiology within systems physiology and neurophysiology, and it establishes the three-tier control architecture — extrinsic autonomic, intrinsic enteric local reflex, and sensory/afferent — by which GI function and perfusion are regulated, with only the afferent tier reaching conscious perception.
Autonomic innervation of the gastrointestinal tract operates on a principle of reciprocal antagonism: sympathetic outflow, arising from thoracic and lumbar segments of the spinal cord and relaying th…