Large Intestines / IBS Flashcards
Where do the large intestines run from and to?
From the caecum to the anal canal
What epithelium lines the large intestines?
Mainly columnar epithelium except the final 1/2 of the anal canal which is stratified squamous epithelium
What is the function of the large intestine?
- Removes water from indigestible gut contents
- Turns chyme into a semi solid
- Produces vitamins
- Acts as temporary storage until defecation
Where does colonic mucosa get the majority of its nutrients from?
From short chain fatty acids derived from fermentation of dietary fibre
How do the different parts of the large intestine lie within the peritoneum?
- Ascending and Descending colon are retroperitoneal
- Transverse colon is intraperitoneal and has its own mesentry
- Sigmoid colon has its own mesentery
- Rectum
- Upper 1/3 intraperitoneal
- Middle 1/3 retroperitoneal
- Lower 1/3 no peritoneum
Describe the arterial supply to the midgut
What is the marginal artery of the midgut?
The anastamoses of the distal ends of all the branches of the SMA that supply the midgut
Describe the Arterial supply of the hindgut
Branches off the Inferior Mesenteric Artery
- Left colic - descending colon
- Sigmoid arteries - descending colon and sigmod colon
- Superior rectal artery - upper 1/3 rectum
Describe the venous drainage of the abdomen
- Midgut - drains into superior mesenteric vein
- Hindgut - drains into inferior mesenteric vein
- Rectum
- upper 1/3 drains into superior rectal vein into IMC
- Middle and lower 1/3 drains into systemic venous system bypassing the liver
How does the Large intestine differ from the small intestine visually?
- Large intestine is shorter and wider
- Has crypts not villi
- Haustra - incomplete rings instead of plica circulares
How are haustra of the large intestine formed?
Incomplete external longitudinal muscles form 3 distinct bands (teniae coli)
Contraction of the teniae coli forms the sacculations known as haustra
How is water absorbed in the large intestine?
ENaC channels on the apical membrane take water into the colon cells
Water folows the the movement of Na+ and follows through tight junctions
Which hormones adds ENaC channels to the apical surface of the cells of the colon?
Aldosterone
Why are tight junctions in the large intestine much tighter than those in the small intestine?
- Allows a bigger gradient to form
- Don’t get any backflow of ions
How does the incidence of IBS change with age?
Peaks in young adults ~ 20 years and a smaller peak ~50 years
What are the key differences between Crohn’s Disease and Ulcerative Collitis?
Crohn’s Disease:
- Affects anywhere in GI tract
- Mainly involves the Terminal Ileum
- Transmural - through the entire wall of the bowel
- Skip lesions
Ulcerative Colitis:
- Begins in the rectum
- Continuous pattern
- Mucosal inflammation (shallow - not the whole wall)
What features would you see on endoscopy in someone with Crohn’s Disease?
- Cobblestone appearance
- Skip lesions
- Fistulae
- Strictures
- Mucosal oedema
- Red and inflammed
- Deep ulcers
What would you see microscopically in someone with Crohn’s disease?
Granuloma Formation
Central granuloma with epithelioid macrophages
What histological changes would you see in a patient with ulcerative colitis?
- Chronic inflammatory infilitrate of lamina propria
- Crypt abscesses
- Crypt distortion → irregular shaped glands, dark crowded nuclei
- Reduced number of goblet cells
What pathological changes would you see on colonoscopy of someone with ulcerative collitis?
- Pseudopolyps (develop after repeated episodes)
- Loss of Haustra
What Radiology features would you see on a barium follow through in Crohn’s disease?
Can sometimes see long strictures → string sign of kantour
What Radiology features would you see on a double contrast enema in Ulcerative Colitis?
- Lead pipe colon - loss of haustra
- Continuous lesions without skipping
- Mucosal inflammation causes granual appearance
