Large Intestines / IBS

Question 1

Where do the large intestines run from and to?

Answer 1

From the caecum to the anal canal

Question 2

What epithelium lines the large intestines?

Answer 2

Mainly columnar epithelium except the final 1/2 of the anal canal which is stratified squamous epithelium

Question 3

What is the function of the large intestine?

Answer 3

• Removes water from indigestible gut contents
• Turns chyme into a semi solid
• Produces vitamins
• Acts as temporary storage until defecation

Question 4

Where does colonic mucosa get the majority of its nutrients from?

Answer 4

From short chain fatty acids derived from fermentation of dietary fibre

Question 5

How do the different parts of the large intestine lie within the peritoneum?

Answer 5

• 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

Question 6

Describe the arterial supply to the midgut

Answer 6

Question 7

What is the marginal artery of the midgut?

Answer 7

The anastamoses of the distal ends of all the branches of the SMA that supply the midgut

Question 8

Describe the Arterial supply of the hindgut

Answer 8

Branches off the Inferior Mesenteric Artery

• Left colic - descending colon
• Sigmoid arteries - descending colon and sigmod colon
• Superior rectal artery - upper 1/3 rectum

Question 9

Describe the venous drainage of the abdomen

Answer 9

• 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

Question 10

How does the Large intestine differ from the small intestine visually?

Answer 10

• Large intestine is shorter and wider
• Has crypts not villi
• Haustra - incomplete rings instead of plica circulares

Question 11

How are haustra of the large intestine formed?

Answer 11

Incomplete external longitudinal muscles form 3 distinct bands (teniae coli)

Contraction of the teniae coli forms the sacculations known as haustra

Question 12

How is water absorbed in the large intestine?

Answer 12

ENaC channels on the apical membrane take water into the colon cells

Water folows the the movement of Na⁺ and follows through tight junctions

Question 13

Which hormones adds ENaC channels to the apical surface of the cells of the colon?

Answer 13

Aldosterone

Question 14

Why are tight junctions in the large intestine much tighter than those in the small intestine?

Answer 14

• Allows a bigger gradient to form
• Don’t get any backflow of ions

Question 15

How does the incidence of IBS change with age?

Answer 15

Peaks in young adults ~ 20 years and a smaller peak ~50 years

Question 16

What are the 2 main types of inflammatory bowel disease?

Answer 16

• Crohn’s Disease
• Ulcerative Colitis

Question 17

What are the key differences between Crohn’s Disease and Ulcerative Collitis?

Answer 17

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)

Question 18

What extra- intestinal problems are associated with inflammatory bowel disease?

Answer 18

• MSK Pain (Arthritis)
• Skin - Erythema nodosum, pyoderma gangernosum, psoriasis
• Primary Sclerosing Cholangitis of the biliary tree
• Eye problems

Question 19

What causes inflammatory bowel disease?

Answer 19

• Genetic element
• Unbalance gut colony
• Immune response
• Potentially triggered by; antibiotics, infection, smoking, diet

Question 20

How would someone with Crohn’s disease present?

Answer 20

• Young patient
• Frequent loose stools
• Non- Bloody stools
• RLQ pain (inflammed terminal ileum)
• Mild perianal inflammation ulceration
• Mildy anaemic

Question 21

What peri-anal disease would you seen in Crohn’s disease?

(specific to Crohn’s, not seen in UC)

Answer 21

• Haemmoroids
• Skin Tags
• Anal Fissure
• Peri- anal abscess

Question 22

What features would you see on endoscopy in someone with Crohn’s Disease?

Answer 22

• Cobblestone appearance
• Skip lesions
• Fistulae
• Strictures
• Mucosal oedema
• Red and inflammed
• Deep ulcers

Question 23

What would you see microscopically in someone with Crohn’s disease?

Answer 23

Granuloma Formation

Central granuloma with epithelioid macrophages

Question 24

How would you investigate someone with suspected Crohn’s Disease?

Answer 24

• Bloods - check for anaemia
• CT/ MRI - looking for bowel wall thickening, obstruction, extra mural problems
• Barium Enema - identifies strictures / fistulae

Question 25

How would someone with ulcerative colitis typically present?

Answer 25

* Young (mid 20s) * Freqeunt passing of **bloody stools** * **Mucus in stools** * Weight loss * Lower abdominal pain/ cramping * Painful Red Eye * **No perianal disease**

Question 26

What histological changes would you see in a patient with ulcerative colitis?

Answer 26

* Chronic inflammatory infilitrate of lamina propria * **Crypt abscesses** * **Crypt distortion** → irregular shaped glands, dark crowded nuclei * **Reduced number of goblet cells**

Question 27

What pathological changes would you see on colonoscopy of someone with ulcerative collitis?

Answer 27

* Pseudopolyps (develop after repeated episodes) * Loss of Haustra

Question 28

What tests would you do if you suspected someone has ulcerative colitis?

Answer 28

* **Bloods** - check for anaemia and serum markers * **Stool cultures** * **Colonoscopy** * **Barium Enema** (mild cases only) * Plain abdominal radiographs

Question 29

What is intermediate colitis?

Answer 29

In 10% of cases Crohn's Disease and Ulcerative Colitis cannot be separated , despite diagnostic evaluation

Question 30

What Radiology features would you see on a barium follow through in Crohn's disease?

Answer 30

Can sometimes see long strictures → **string sign of kantour**

Question 31

What Radiology features would you see on a double contrast enema in Ulcerative Colitis?

Answer 31

* **Lead pipe colon** - loss of haustra * Continuous lesions without skipping * Mucosal inflammation causes granual appearance

Question 32

What is pancolitis?

Answer 32

Inflammation of the entire colon

Question 33

What drugs can you give to treat IBD?

Answer 33

1. Aminosalicylates 2. Corticosteroids 3. Immunomodulators

Question 34

How can you surgically manage crohn's and ulcerative colitis?

Answer 34

**Crohn's** * surgery not curative * Remove strcutres and fistulas * Conservative - remove as luttle bowel as possible **UC** * surgery can be curable (colectomy) * Remove entire colon * Used if inflammation not settling, precancerous changes of toxic megacolon at risk of perforation