GI regulation is through the interplay of autonomic/enteric nervous systems and endocrine/paracrine activity
Autonomic Nervous Regulation
parasympathetic primarily through the vagus nerve (through distal colon)
stimulates salivary/gastric secretion during cephalic phase of digestion
controls gastric motility, biliary and pancreatic secretions
distal colon and rectum innervated through pelvic splancnic nerves
Enteric Nervous Regulation
– considered a separate part of the autonomic nervous system
myenteric plexus controls gut motility (peristalsis, etc)
also can act on submucosal plexus: serotonin (stimulatory); enkephalin (inhibitory)
submucosal plexus: controls epithelial and vascular functions of the mucosa
ACh and VIP are the major neurotransmitters
released onto epithelium and vasculature via diffuse junctions
sympathetic noradrenergic fibers (inhibitory) act on submucosal ganglia and epithelium
Endocrine Regulation
the intestinal mucosa is the largest endocrine organ in the body
endocrine cells are distributed diffusely, scattered throughout the epithelium; they release peptide hormones and biogenic amines (serotonin, histamine)
carboxy terminus is the active portion of peptide hormones; it is often amidated at the carboxy end
many hormones have similar active ends (i.e. gastrin and CCK)
excess production of GI hormones (i.e. tumors) can lead to disease: