Neural Control of GI Motility and Function

Major GI sphincters

Lower Esophageal Sphincter(LES), pyloric valve, ileocecal valve, internal/external anal sphincters.

Layers of GI tract

Mucosa, submucosa, muscularis propria (circular + longitudinal), nerve plexuses(Submucosal and Myenteric), serosa.

Function of mucosa

Secretion, absorption, enzyme activity.

Function of submucosa

Vascular supply, transport, glands.

Function of muscularis propria

Motility; circular + longitudinal smooth muscle.

Myenteric plexus (Auerbach’s)

Controls motor function: contraction strength, peristalsis, sphincter tone.

Submucosal plexus (Meissner’s)

Controls secretion, absorption, mucosal blood flow.

ENS role

Regulates motility, secretion, absorption, blood flow; largest nerve network outside CNS.

Isolated contractions

Small, localized contractions for mixing; mediated by myenteric plexus.

Segmentation

Mixing movement; no net propulsion; enhances digestion and absorption.

Peristalsis

Propulsive movement; oral → caudal; contraction followed by receptive relaxation.

Trigger for peristalsis

Radial stretch of gut wall by chyme.

Migrating Motor Complex (MMC)

Fasting motility pattern; sweeps stomach → ileum every 90 min; clears residual contents.

Gastroenteric reflex

food distension of the stomach + duodenum= inc peristalsis

Arterial supply of GI tract

Celiac artery, SMA, IMA.

Portal circulation

Venous blood from GI → portal vein → liver → hepatic veins → IVC.

Lower esophageal sphincter (LES) function

Prevents reflux; tonically contracted at 10–30 mmHg.

Decrease LES tone

Anticholinergics, caffeine, nitrates, CCBs, PDE inhibitors.

GERD mechanism

Weak LES → acid reflux.

Achalasia mechanism

LES fails to relax → dysphagia; treated with Botox, dilation, surgery.

Gastric emptying

~10 mL per contraction; full emptying ~4–5 hours.

Increase gastric emptying

Food volume, vagal tone, gastrin.

Decrease gastric emptying

Low duodenal pH, high osmolality, fats, proteins, distension.

Dumping syndrome

Rapid emptying after pylorus bypass; nausea, diarrhea, hypotension; treat with small meals.

Gastroparesis

Delayed emptying and gastric motility due to diabetes/vagal injury; early satiety, nausea; treat with metoclopramide or DM control.

Small bowel peristalsis; Mediated by?

Propels chyme ~1 cm/min; increases mucosal exposure. Mediated by myenteric plexus

Post-Operative Ileus

Absent peristalsis due to surgery, opioids, critical illness.

Intestinal pseudo‑obstruction

Obstruction‑like symptoms without blockage; due to neuromuscular disease(sclerodema) or vasculitis.

Ileocecal valve function

Prevents colonic backflow; reduces bacterial overgrowth.

Gastroileal reflex

Stomach distension → relaxes ICV → promotes ileal emptying.

Cecal stretch reflex

Cecal distension → contracts ICV → inhibits ileal peristalsis.

Right colon function

Water and electrolyte absorption.

Left colon function

Fecal storage.

Haustrations

Non‑propulsive mixing contractions.

Gastrocolic reflex

Stomach distension triggers colonic mass movements.

Ileocecal Valve resection effects

Diarrhea, Small Intestine Bacterial Overgrowth (SIBO), loss of ileal brake. (often due to cancer or crohn’s disease)

Constipation mechanism

Slow transit, ENS damage, excessive water absorption.

Diarrhea mechanism

Fast transit or unabsorbable osmoles.

Recto‑anal inhibitory reflex (RAIR)

Rectal distension → Internal anal sphincter relaxation.

Hirschsprung disease

Absent myenteric plexus in distal colon → no recto-anal inhibitory reflex(no internal anal sphincter relaxation) → severe constipation.

Spinal cord injury effect

Loss of voluntary control due to disrupted pelvic motor/sensory nerves; ENS reflexes intact; bowel retraining possible.

Goldilocks: LES

Too tight = achalasia; too loose = GERD.

Goldilocks: pylorus

Too tight = gastric outlet obstruction; too loose = dumping syndrome.

Goldilocks: Ileocecal valve

Too tight = SBO; too loose = diarrhea/SIBO.

Goldilocks: internal anal sphincter

Too tight = Hirschsprung/dyssynergia; too loose = incontinence.

Goldilocks principle: stomach motility

Too fast = dumping syndrome; too slow = gastroparesis;

Goldilocks principle: small bowel motility

Too fast = diarrhea/malabsorption; too slow = pseudo‑obstruction/SIBO;

Goldilocks principle: colonic motility

Too fast = diarrhea/incontinence; too slow = slow‑transit constipation;

Goldilocks principle: esophageal motility

Too slow = dysphagia; too fast is uncommon;