The Large Intestine Flashcards
Describe the cellular structure of the large intesine and what the luminal surface looks like
Large intestine has a simple columnar epithelium with numerous crypts of Lieberkuhn
Luminal surface does not have any villi but instead has haustra (folds) formed by the contraction of teniae coli - external longitudinal muscle spilt into three bands
How does the colonic mucosa obtain its nutrients
Majority of colonic nutrients come from fermentation of dietary fibre
Fermentation produces short chain fatty acids which are uesd by the mucosa
What is the arterial supply to the colon
SMA gives off:
- Ileo-coli - caecum
- Right colic - ascending colon
- Middle colic - proximal 2/3 transverse colon
IMA gives off:
- Left colic - descending and distal 1/3 transverse colon
- Sigmoid - descending colon
- Superior rectal - upper 1/3 rectum
What is the marginal artery
Continuous arterial arcade along the inner border of the colon formed by anastomoses between the terminal branches of the superior and inferior mesenteric arteries
What veins drain the colon
Superior mesenteric vein drains caecum, ascending and proximal 2/3 transverse colon
Inferior mesenteric vein drains sigmoid, distal 1/3 transverse and descending colon
What are the functions of the colon
Water reabsorption
Temporary storage
Final electrolyte absorption and some bile salt absorption
What is the gastrocolic reflex
A relfex generate by eating that causes movement in the GI tract
Stimulates contractions in the large intestine that causes bowel movement
What are the functions of the bacteria in the colon
Synthesis of vitamins
Breakdown of primary to secondary bile acids
Conversion of bilirubin to non-pigmented metabolites
How is water reabsorbed in the colon and what adaptations aid water reabsorption
Water reabsorption is facilitated by ENaC - create an osmotic gradient for water to follow
Tight junctions between cells aids water reabsorption as it allows for a large ion gradient to form and prevents diffusion of ions back into the lumen
What is inflammatory bowel disease
Group of conditions characterised by idiopathic inflammation of the GI tract
Typically affects younger pepole and those aged 40-60
What are some extra-intestinal probelms that IBD can cause
MSK pain - arthritis
Skin - psoriasis, erythema nodosum, pyoderma gangrenosum
Liver/billary tree pathology - PSC
Eye problems
What is Crohn’s disease
Inflammation of the colon
Affects anywhere in the colon but normally affects ileum, typically terminal ileum
CD is transmural inflammation -> goes through the bowel
Has skip lesions -> has patches of inflammation and patches of normal bowel
How can a patient with Crohn’s disease present
History of loose stools - non-bloody
Weight loss
Right lower quadrant pain
Tender mass in RLQ
Some joint pain
Smoker
Mild perianal inflammation/ulceration - may have fistula
Low grade fever
Mildly anaemic
What gross pathology can be seen in Crohn’s disease
Skip lesions
Hyperaemia
Mucosal oedema
Superficial and/or deep ulcers
Transmural inflammation causing thickening of bowel wall and narrowing of the lumen
Cobblestone appearance
Fistulae - between bowel and bowel/bladder/vaagina/skin
What investigations can be done with Crohn’s disease
Bloods - anaemia and raised CRP
CT/MRI - wall thickening, obstruction, extramural problems
Barium enema/follow through
Colonoscopy
Radiology using barium follow through - look for strictures and/or narrowing
What is ulcerative colitis
Inflammation of the colon that begins in the rectum -> extends proximally to involve entire colon
Has continuous pattern
Only causes mucosal inflammation -> superficial
Can cause backwash ileitis if it spreads to the terminal ileum
How can a patient with ulcerative colitis present
History of bloody stools
Weight loss
Mild lower abdominal pain/cramping
Painful red eye
Mildly tender abdomen
No perianal disease
Normal temperature
What pathological changes occur in ulcerative colitis
Chronic inflammatory infiltrate of lamina propria
Crypt abscesses - neutrophilic exudate in crypts
Crypt distortion - due to repeated inflammation and healing
Reduced goblet cell number and reduce bacteria
Pseudopolyps - after repeated episodes of inflammation and healing
Loss of haustra
Friable mucosa - easy bleeding
What investigations can be performed for a patient with suspected ulcerative colitis
Bloods - anaemia and serum markers
Stool culture
Colonoscopy
Plain abdominal radiograph - can show loss of haustra, mucosal inflammation (appears granulated)
Barium enema
CT/MRI - used to look for toxic megacolon
What are the treatments for IBD
Stepwise approach used with pharmacological treatment:
- Aminosalicytes - flares and remission.
- Corticosteroids for flares
- Immunomodulators for fistulas and long term control
Surgery:
- Crohn’s - remove affected parts of the bowel
- UC - remove whole bowel
What features can be seen under the microscope in Crohn’s Disease
Granulomas
Organised collection of epithelioid macrophages
