18. IBS Flashcards
3 main functions of bowel motility
Mixing of intestinal contents
Bringing contents into contact with small bowel wall
Forward propulsion
2 types of gross contractility seen in the fed state
1) Segmentation – discontinuous oscillating contractions which mixes the luminal contents, and brings it into contact with the small bowel wall
2) Peristaltic contractions, these longitudinal contractions are initiated by distension of the bowel wall. This causes rapid propulsion of contents towards the anus, at 2-25cm/second.
Fasting state
migrating motor complexes (MMC) occur every 90-120 minutes
high frequency burst of powerful contraction
from stomach to terminal ileum
moves along indigestible food, dead cells, bacteria, and keeps colonic bacteria out of the small bowel
Segmental contractions (Large Bowel)
1) taeniae coli gather the colon into haustra
2) distension leads the haustra to contract
3) bolus moves forward
4) contraction of adjacent haustra, leads to mixing
5) Increased contact with the bowel wall for absorption
6) Initiated by ach and substance P
Peristalsis (Large Bowel)
slower in the large intestine
slow waves of propulsive contractions
initiated by distension
controlled by vagal inhibitory or excitatory fibres
Mass Movement (Large Bowel)
from mid-transverse colon to the rectum
occur a few times a day
leads to colonic evacuation
partly vagal mediated, but also involves cholecystokinin
Meissner’s submucosal and Auerbach’s myenteric plexuses
present in walls of the colon
modulated by parasympathetic and sympathetic supplies
vagal nerve and pelvic nerve parasympathetic supply
increases proximal colon contraction
increases salt and water absorption
The inferior mesenteric, superior mesenteric and hypogastric plexuses
provide sympathetic innervation
decreases colonic movement
The colo-colonic reflex
stimulated by the sympathetic plexuses
causes one part of colon to relax whilst adjacent is distended
IBS
recurrent abdominal pain associated with altered defecation in the absence of organic disease
Common symptoms of IBS
recurrent abdominal pain for at least 3 days per month in the last 3 months, associated with
- Improvement with defecation
- Change in frequency of stool
- Change in appearance of stool
Symptoms of organic bowel disease which are not compatible with IBS include
Age >55 years Rectal bleeding Nocturnal symptoms Weight loss Anaemia FH of colorectal cancer in a first degree relative
Describe common aetiological factors in IBS
most commonly diagnosed GI condition
population prevalence in Europe = 11%
Risks of IBS
1) Food allergy and sensitivity
2) Post-infection IBS
3) Micro-flora
4) Psychosocial factors
5) Genetic susceptibility
