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
Discuss the physiological basis of the symptoms
Distension – stretch receptor hypersensitivity (1).
Bloating – impaired transit of gas loads
Pain – increased serotonins, kinins or spinal cord excitability
Abdominal pain and colonic motility – induced by CRF, released with stressful stimuli
GI motility
Explain the concept of colonic transit time
1) Oro-cecal transit time = measuring the time to an increase in breath hydrogen after a standard meal
2) Colonic transit time = measured using consumed radio-opaque markers, and a plain abdominal X-ray
Discuss basic modalities of investigation and management of IBS
1) History and examination
Check red flags of:
a. Age >55
b. Nocturnal symptoms
c. First degree relative with colorectal cancer
d. Weight loss
e. PR bleeding
If positive for a red flag, refer to secondary care, for consideration for colonoscopy.
2) Bloods
3) Faeces testing for CALPROTECTIN
If these tests are positive, the colonoscopy
If stool culture positive, reassess in a few weeks
If all above is negative, then consider IBS, and manage symptoms:
Diarrhoea – dietary change (FODMAPs), avoid laxatives, consider loperamide or codeine
Constipation – increase roughage in diet, laxatives
Pain and bloating - mebeverine and peppermint oil for spasm
Mebeverine
direct alimentary tract smooth muscle
relaxant
Codeine
opiate
antidiarrheal
Loperamide
opioid receptor agonist
not crossing the blood brain barrier
Amitriptyline
tricyclic antidepressant
used to help neuropathic nociception
CCK (cholecystokinin) GI source
Enteroendocrine cells in upper intestine
CCK signal for release
Duodenal peptide, amino-acid, fat or Na
CCK motility action
Contracts the gall-bladder
Relaxes the sphincter of Oddi
Delays gastric emptying
Contracts pylorus
Secretin GI source
S cells in small intestine
Secretin signal for release
Duodenum acid and fat digestive products
Secretin motility action
Contracts pylorus (and stimulates CCK)
Gastrin GI source
G cells, antrum stomach
Gastrin signal for release
Stomach distension
vagal stimulation
peptides in stomach
Gastrin motility action
Causes ileal segmentation (gastro-ilial reflex)
Increased gastric motility
closes lower oesophageal sphincter
increases acid secretion and insulin secretion
Somatostatin GI source
D cells of pancreatic islets, intestinal cells
Somatostatin signal for release
Glucose amino acids free fatty acids glucagon beta-adrenergic and cholinergic neurotransmitters
Somatostatin motility action
Decreases gastric, duodenal and gall bladder motility
