# Colonic Motility Physiology > Colonic motility in MBBS Physiology: haustral mixing, mass movements, gastrocolic reflex, colonic absorption and Hirschsprung disease. - Canonical URL: https://prepelephant.com/topics/mbbs/physiology/colonic-motility-physiology - Exam / course: MBBS · Subject: Physiology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Colonic Motility Physiology", PrepElephant, https://prepelephant.com/topics/mbbs/physiology/colonic-motility-physiology ## Direct answer Of the roughly nine litres of fluid the gut handles daily, the colon receives 1-1.5 litres and absorbs all but 100-200 mL that appear in stool — its absorptive duty performed while three motor patterns move contents slowly: haustral segmentation (mixing and absorption by contraction of the taeniae-bordered haustra), multihaustral propulsion, and the mass movements that sweep the colon one to three times a day, classically after meals through the gastrocolic and duodenocolic reflexes. Transit is correspondingly slow — colonic transit of 12-48 hours — allowing the microbiota to ferment residual fibre into short-chain fatty acids in parallel. The motor apparatus depends on the enteric plexuses: aganglionosis of the submucosal and myenteric plexuses in a rectosigmoid segment abolishes the rectoanal inhibitory reflex and peristalsis there, producing Hirschsprung disease — a tonically contracted segment with proximal megacolon, confirmed by suction rectal biopsy. ## What you must remember - **Fluid balance:** about 9 litres traverse the gut daily; the small intestine absorbs 7-8 litres, the colon 1-1.5 litres, leaving 100-200 mL in stool — the colon's reserve capacity is why small-intestinal disease causes profuse watery diarrhoea while colonic disease rarely exceeds a few hundred millilitres per day. - **Motor patterns:** haustral (segmentation) contractions 3-8 per minute mix and expose contents for absorption; peristaltic waves move contents caudad slowly; mass movements — 1-3 per day, strongest after breakfast — carry contents long distances in seconds. - **Gastrocolic reflex:** gastric filling and duodenal fat and acid trigger colonic mass movements, mediated by gastrin, CCK and autonomic reflexes — the reason defecation urge follows breakfast, and why morning routines matter in constipation clinics. - **Transit numbers:** mouth-to-anus about 24-72 hours; the colonic share is 12-48 hours — measured clinically by the Sitzmarker (radio-opaque marker) study for slow-transit constipation. - **Hirschsprung physiology:** absence of ganglion cells in Meissner's and Auerbach's plexuses in a distal segment (RET pathway mutations; incidence about 1 in 5,000, male predominance near 4:1) — tonically contracted segment, absent rectoanal inhibitory reflex on anorectal manometry, and suction rectal biopsy is the diagnostic standard. - **Fermentation physiology:** the colonic bacteria convert unabsorbed carbohydrate into hydrogen, methane and short-chain fatty acids — the basis of breath tests for carbohydrate malabsorption (lactose, fructose) and for small-intestinal bacterial overgrowth. - **Clinical correlations:** diverticulosis follows low-fibre, high-pressure segmentation in the sigmoid; Chagas disease destroys myenteric plexus and produces megacolon — named diseases for postgraduate vivas. ## A worked case from neonatal constipation A newborn fails to pass meconium within 48 hours and develops abdominal distension. The rectum is empty on examination — because the distal aganglionic segment cannot relax or propagate, everything proximal accumulates and dilates. Rectoanal manometry shows no internal sphincter relaxation on balloon distension (absent rectoanal inhibitory reflex), contrast enema shows a narrow rectosigmoid with a cone-shaped transition to dilated proximal colon, and suction rectal biopsy — increased acetylcholinesterase staining, absent ganglion cells — confirms Hirschsprung disease. The physiology decides the surgery: resect the aganglionic segment and pull through innervated bowel. Contrast an adult with lifelong constipation and a marker study showing fivefold-normal transit — slow-transit constipation, treated with fibre, osmotics and prokinetics. The two cases share a symptom and diverge at the plexus — the reasoning structure the integrated viva tests. ## Where students slip Students credit mass movements with continuous propulsion; they are episodic, occurring one to three times daily, and most colonic time is spent mixing — hence the long transit. The second slip is confusing the gastrocolic reflex with the defecation reflex: the gastrocolic fills the rectum; the defecation reflex empties it — two steps of one morning routine. Third, in Hirschsprung disease the dilated segment is proximal and normal (secondarily dilated), while the abnormal segment is the narrow distal one — candidates frequently reverse this on contrast-film descriptions. Fourth, colonic fluid absorption is active sodium-coupled transport, not passive seepage — the reason the colon compensates after small-bowel resection. ## Frequently asked questions ### How much fluid does the colon absorb daily? Of roughly 9 litres presented to the gut, the colon receives 1-1.5 litres and absorbs all but 100-200 mL excreted in stool, with reserve capacity that can triple when the small intestine is diseased or resected. ### What are mass movements and when do they occur? Powerful multihaustral propulsive contractions sweeping the colon one to three times daily, typically within minutes of meals through the gastrocolic reflex — the mechanism that fills the rectum and provokes the urge to defecate. ### What is the manometric hallmark of Hirschsprung disease? Absent rectoanal inhibitory reflex — internal anal sphincter fails to relax on rectal balloon distension — because the aganglionic distal segment lacks the enteric reflex arc; suction rectal biopsy confirms absent ganglion cells. ### Which study quantifies colonic transit in chronic constipation? The radio-opaque marker (Sitzmarker) study — swallowed markers radiographed over 3-5 days; delayed elimination indicates slow-transit constipation when anorectal disorders are excluded. ### Why do breath tests diagnose carbohydrate malabsorption? Colonic bacteria ferment malabsorbed carbohydrate to hydrogen and methane, which are absorbed, carried to the lungs and exhaled — a rise after a lactose or glucose load localises the digestive defect.