Large Intestine & Inflammatory Bowel Disease

Question 1

Describe the gross & microscopic anatomy of the large intestines and relate these it’s function

Answer 1

• Columnar epithelium
• No folds (plicae circulares), no villi, some microvilli
• Has crypts
• Much shorter and wider than the small intestine
• External longitudinal muscle is incomplete
  
  • 3 distinct bands - teniae coli
    Have haustra which are sacculations caused by contraction of teniae coli
    
    • Draw-string like interaction
  • The teniae coli are shorter than the intestine, so intestine forms sac-like structures called haustra

Question 2

Describe the functions of the large intestine

Answer 2

• Absorption of water from the indigestible gut contents
  
  • Turns chyme into a semi solid
  • Facilitated by EnaC, which is sensitive to aldosterone
  • Occurs mainly in the ascending and transverse colon
  • Strong tight junctions to prevent water from escaping back into the lumen
  • Water absorption occurs transcellularly
• Production of certain vitamins
• Acts as temporary storage until defecation
  
  • Faeces stored in descending colon

Question 3

Describe the motility of the colon and rectum

Answer 3

• Haustral contractions are slow segmenting, uncoordinated movements that occur every 25 min
• One haustrum distends and fills with chyme
• Teniae coli contract which pushes the contents to the next haustrum

Question 4

Define mass movement

Answer 4

Waves of intense contractions within the large intestine which cause movement of large masses of chyme from one portion to the next

Question 5

Explain the gastro-colic reflex

Answer 5

• Increase in motility of large intestine in response to stretching of stomach
• Movement of faeces into rectum
• As fecal material collects in the rectum, it increases the pressure instead giving the urge to defecate

Question 6

Describe the causes of intestinal inflammation and infection

Answer 6

• Genetic
• Gut organisms
• Immune response
• Smoking - associated with Crohn’s

Question 7

Describe the presentation of Crohn’s

Answer 7

• Affects 15-30 and 60+
• Affects anywhere in GI tract
  
  • Ileum involved in most cases
• Non-bloody loose stools
• Weight loss
• Right lower quadrant pain
• Associated with smoking

Question 8

Describe the presentation of ulcerative colitis

Answer 8

• Affects young adults
• Begins in rectum and moves proximally
  
  • Can extend to involve entire colon
• Multiple bloody stools per day
• Weight loss
• Mild lower abdominal pain/cramping
• Painful red eye

Question 9

What are extra-intestinal problems that occur form Crohn’s and UC

Answer 9

• MSK pain - arthritis
• Skin - erythema nodosum - bruise like swelling due to inflammation of fat cells
  
  • Psoriasis
• Liver/biliary tree
• Eye problems

Question 10

How would you investigate for Crohn’s

Answer 10

• Blood test - anaemia
• CT/MRI scans - bowel wall thickening, obstruction from strictures
• Barium enema/follow through
  
  • Barium swallowed and then tracked throughout GI tract as Crohn’s can affect anywhere along the GI tract
  • Identify fistula and strictures
• Colonoscopy - can’t investigate small intestine due to constant muscle contractions

Question 11

How would you investigate for UC

Answer 11

• Blood test - anaemia, serum markers
• Stool cultures
• Plain abdominal radiographs
• Barium enema - in mild cases
• CT/MRI scans
• Colonoscopy

Question 12

Describe the changes to the intestines that occur in Crohn’s

Answer 12

• Transmural - inflammation through the wall
  
  • Thickening of bowel wall - scarring due to constant inflammation and healing
  • Narrowing of lumen
  • Constant healing can result in fistula formation
    
    • Eg. From bowel to vagina/bladder
    • Bowel contents move into abnormal area
• Skip lesions - patterns of patches of affected gut then patches of unaffected gut
• Hyperaemia - excess blood in vessels supplying organ causing red swelling
• Mucosal oedema
• Discrete superficial ulcers and deeper ulcers
• Cobblestone appearance - regenerating tissue and oedematous mucosa with deep ulcers in-between
• Granuloma formation

Question 13

Describe the changes to the intestines in UC

Answer 13

• Chronic inflammatory infiltrate of lamina propria
• Crypt abscesses - crypt distortion
• Continuous pattern of ulceration
• Mucosal inflammation
• Goblet cells
• Pseudopolyps - islands of mucosa
• Loss of haustra

Question 14

Distinguish between Crohn’s and UC

Answer 14

• Crohn’s anywhere along GI tract, UC in colon/rectum
• UC involves gross bleeding
• Crohn’s has perianal disease
• Crohn’s has fistula formation
• Crohn’s potentially causes malnutrition
• Crohn’s has transmural inflammation, UC localised to mucosa
• Crohn’s has granulomas
• Crohn’s causes fibrosis
• UC has crypt abscess formation
• Crohn’s mucosal involvement in skip lesions while UC continuous

Question 15

Describe the common treatment options that are available for inflammatory bowel disease

Answer 15

• Anti-inflammatory drugs
  
  • Aminosalicylates - specific for Crohn’s and ulcerative colitis
  • Corticosteroids
  • Immunomodulators
• Surgical
  
  • Crohn’s
    
    • Not curative
    • Strictures/fistulas from inflammation
    • As little bowel removed as possible - need to maintain surface area for water reabsorption as already compromised in inflamed small intestine
  • Ulcerative colitis
    
    • Curable - colectomy