Session 8 - Large Intestine And IBD Flashcards
What are the functions of the large intestine?
Removal of water from indigestible gut contents - turns chyme into a semi solid.
Acts as a temporary storage until defaecation.
Production of certain vitamins (e.g. vitamin K is produced by bacteria in the large intestine).
Describe the appearance of the lining of the large intestine to the naked eye.
Flat surface, no plicae circulares or villi.
Has teniae coli (three distinct bands of longitudinal muscle)
Haustra
Describe the structural differences between the large intestine and small intestine.
The large intestine:
- is much shorter
- is much wider
- has crypts not villi
- has incomplete longitudinal muscle forming teniae coli
- has haustra
- has no plicae circulares
What is the gastrocolic reflex?
Mass movement of the contents of the colon into the rectum, triggered by food entering the stomach after eating.
How does water absorption occur in the colon?
Facilitated by ENaC.
Sodium moves into epithelial cell via epithelia sodium channel (ENaC).
Water follows the sodium into cell through aquaporins.
What is inflammatory bowel disease?
A group of conditions characterised by idiopathic inflammation of the GI tract.
What are the two most common types of inflammatory bowel disease?
Crohn’s disease
Ulcerative colitis
Who is most commonly affected by Crohn’s disease?
15-30 yr olds and 60+ yr olds
Who is most commonly affected by ulcerative colitis?
Young adults
Give examples of types of inflammatory bowel disease other than Crohn’s disease or ulcerative colitis.
Diversion colitis
Pouchitis
Microscopic colitis
What are the differences between Crohn’s disease and ulcerative colitis?
Crohn’s disease:
- affects anywhere in the GI tract
- ileum involved in most cases
- transmural (deep inflammation, through the wall)
- skip lesions (unaffected areas of mucosa in between affected areas)
Ulcerative colitis:
- begins in the rectum, move proximally
- can extend to involve entire colon
- continuous
- superficial mucosal inflammation
What problems can inflammatory bowel disease cause outside of the intestines?
MSK pain - arthritis
Skin - erythema nodosum, pyoderma gangrenosum, psoriasis
Liver/biliary tree - primary sclerosis cholangitis (PSC)
Eye problems
What are the possible causes of inflammatory bowel disease?
Not entirely clear. Multifactoral with a genetic element.
- genetics
- altered interaction with gut organisms
- immune response (possibly to antibiotics, infections, smoking, diet)
How would Crohn’s disease present?
Loose non-bloody stools
Weight loss
Right lower quadrant pain
What gross pathological processes are visible in a bowel with Crohn’s disease?
Cobblestone appearance
Hyperaemia (increase blood flow to tissues)
Mucosal oedema
Discrete superficial ulcers,
Deep ulcers
Transmural inflammation (can lead to thickening of the bowel wall due to scar tissue and narrowing due to strictures)
Fistulae (e.g. between bowel and bladder)
What microscopic finding is pathognomonic of Crohn’s disease?
Granuloma formation
What investigations would you use to help diagnose Crohn’s?
Colonoscopy - look for ‘cobblestone’ appearance and ulcers
Bloods - anaemia
CT/MRI scans - bowel wall thickening, obstruction, extramural problems
Barium enema/follow through - strictures/fistulae
How would ulcerative colitis present?
Bloody stools Weight loss Mild lower abdominal pain/cramping Normal temp No perianal disease
What pathological changes occur in ulcerative colitis?
Chronic inflammation of the lamina propria
Crypt abscesses
Pseudopolyps (islands of regenerating mucosa)
Loss of haustra
What investigations would you use to help diagnose ulcerative colitis?
Colonoscopy Bloods - anaemia, serum markers Stool cultures Plain abdominal radiographs Barium enema CT/MRI
What is meant by intermediate colitis?
IBD that cannot be classified into UC or Crohn’s even after diagnostic evaluation. Has characteristics of both.
What medical treatments are used for Crohn’s disease and ulcerative colitis?
- Aminosalicylates (e.g. sulfasalazine) - for flares and remission
- Corticosteroids (e.g. prednisolone) - for flares only
- Immunomodulators (e.g. azathioprine) - for fistulas and maintenance of remission
Can surgery cure Crohn’s disease?
No, as you can’t remove every skip lesion without removing too much of the small intestine.
Can surgery cure ulcerative colitis?
Yes, through a colectomy.
In what cases would a colectomy be considered to treat ulcerative colitis?
If the inflammation is not settling, there are precancerous changes or a toxic megacolon.
What is toxic megacolon?
Toxic megacolon is the clinical term for an acute toxic colitis with dilatation of the colon. The dilatation can be either total or segmental. It is a complication of ulcerative colitis, and more rarely Crohn’s disease.
