Large intestine/ iBD Flashcards
What is the large intestine made up of? What epithelium does it have?
Caecum Ascending colon Transverse colon Descending colon Sigmoid colon Rectum Anal canal
Simple Columnar (bar distal anus= simple squamous)
What are the functions of the large intestine?
Removes water from all the indigestible gut contents (proximal)
Produces vitamins
Microbiome
Temporary storage until defaecation (distal) T&D C -> rapid peristalsis
Ferments dietary fibre -> short chain fatty acids + CO2/ methane/ H2 gas
Explain the peritoneum of the large intestine
Ascending and descending colon are retro-peritoneal
Transverse colon has its own Mesentery (transverse mesocolon) intra-peritoneal
Sigmoid colon has own Mesentery (can form volvulus)
Rectum upper 1/3 intra-peritoneal
Middle 1/3 retroperitoneal
Lower 1/3 no peritoneum
What is the large intestine arterial supply to each part?
Midgut component - superior mesenteric artery: Ileo-colic -> Caecum Right colic -> AC Middle colic -> transverse colon (Jejunal and Ileal arteries)
Terminal branches of SMA form anastomoses network around periphery of bowel ‘marginal artery’
Hindgut component - IMA:
Left colic -> Dc
Sigmoid arteries -> SC
Superior rectal A -> upper 1/3 rectum
Venous drainage of the large intestine?
Midgut (caecum, AC, TC) -> superior mesenteric vein
Hindgut (DC, SC) -> IMV
Rectum: upper 1/3 -> Superior rectal vein (IMV), middle and lower -> systemic venous system = portosystemic anastomosis (thin walled)
Differences between structure large and small intestine
Large: shorter, wider, has crypts not villi, external longitudinal muscle is incomplete - 3 distinct bands (teniae coli) - haustra are sacculations caused by contraction of teniae coli (+ complete circular muscle), has epiploic appendices (fatty tags)
SI doesn’t
How does the colon absorb water?
ENaC channel on apical membrane (conc grad set up by NAK pump basolateral and K channel apical)
Induced by aldosterone
1500mls enter colon/ day, <100mls excreted faeces
Most absorption proximal colon
Tighter junctions, less back diffusion of ions
What is inflammatory bowel disease? What are the two most common types? Which age group is most affected?
Group of conditions characterised by idiopathic inflammation of the GI tract. Affect function of the gut.
Including:
Crohn’s disease
Ulcerative colitis (young adults)
20yrs (highest) and 60 peaks of IBD
Compare and contrast Crohn’s disease and ulcerative colitis? including presentation and cause
Crohn’s: affects anywhere GI tract (ileum normally involved), transmural (isolated area(s)) - skip lesions, affects deep tissue, 25% gross bleeding, perianal disease 75%, transmural inflammation (rare UC), granulomas, fibrosis
UC: begins rectum -> can involve entire colon, continuous pattern, mucosal inflammation (shallow), gross bleeding, perianal disease rare, no fistulaes, no malnutrition, crypt abscesses (rare C)
Both can present with:
Extra- intestinal problems- MSK pain (50%) e.g. arthritis, skin (30%) e.g. erythema nodosum/ pyoderma gangrenosum/ psoriasis, liver/ biliary tree e.g. primary sclerosing cholangitis, eye problems (5%)
Both caused by unclear mechanisms involving: genetic element, gut organisms altered interaction, immune response, trigger e.g. antibiotics, infections, diet
Smoking: cause of Crohn’s but settles UC
Crohn’s disease symptoms and gross/ microscopic pathological
- Unexplained weight loss
- Tender mass RLQ (terminal ileum inflammation)
- frequent, recurring diarrhoea
- low grade fever
- mildly anaemia
Pathology:
- skip lesions
- hyperaemia (XS blood supplied)
- mucosal oedema
- discrete superficial ulcers
- deeper ulcers
- transmural inflammation
- thickening wall -> narrowed lumen
- cobblestone appearance (ulcers between inflamed mucosa)
- fistulae (connections between 2 epithelial lined surfaces) (also occurs bladder/ vagina/ skin)
- granulosa formation = pathognomonic (v characteristic Crohn’s)
Investigating Crohn’s
Bloods - anaemia
CT/ MRI - bowel wall thickening, obstruction, extramural problems
Barium enema/ follow through (oral) - used less but good for demonstrating strictures/ fistulaes - string sign of Kantour (long stricture)
Colonoscopy or endoscopy - gross pathological changes e.g. skip lesions, cobblestone appearance (severe), fistulae, strictures
Ulcerative colitis symptoms and pathological changes
- Mildly tender abdomen
- no perianal disease (skin tag/ fistulae/ ulcers)
- normal temp (unless advanced)
- weight loss
- diarrhoea
Pathological:
- chronic inflammatory infiltrate of lamina propria
- crypt abscesses (neutrophilic exudate)
- crypt distortion (irregular shaped glands with dysplasia, darker crowed nuclei)
- friable mucosa
- reduced goblet cells
- pseudopolyps (inflammation then healing, non neoplastic, more common UCS)
- loss of haustra
Investigating Uc
Bloods - anaemia, serum markers
Stool cultures - blood
Colonoscopy
Plain abdo radiographs
Barium enema (mild cases) - double contrast enema lead pipe colon (no haustra)
CT/MRI (less useful for diagnosing uncomplicated Uc)
What is indeterminate colitis?
Has features of both ulcerative colitis and Crohn’s disease so cant be classified as one or the other (10% of IBD)
pharmacological Treatment options IBD
- Aminosalicylates - for flares and remission
- Corticosteroids - prednisolone flares only
- Immunomodulators fistulaes/ maintenance of remission
