GI13 - Large Intestines & IBD (Crohns & UC), IBS

Question 1

4 features of the structure of the large intestines

Divisions
Relationship w/ Peritoneum
Mesenteries
Large Intestines vs Small Intestines

Answer 1

1.) Divisions - caecum/appendix –> ascending –> transverse –> descending –> sigmoid –> rectum –> anus

2. ) Peritoneum - different relations to the peritoneum
   - ascending and descending colon are retroperitoneal
   - rectum has 3 divisions: upper 1/3 is intraperitoneal, middle 1/3 retroperitoneal, lower 1/3 has no peritoneum
3. ) Mesenteries - transverse and sigmoid have their own
   - transverse has the transverse mesocolon
   - sigmoid colon also has its own which can twist leading to sigmoid volvulus
4. ) Large Intestines vs Small Intestines
   - LI is shorter but wider
   - LI has haustra (sacculations) caused by contraction of teniae coli (bands of longitudinal muscle)
   - LI has epiploic appendices (small, fat filled pouches)

Question 2

4 functions of the large intestines

Answer 2

1. ) Water Absorption - removes water from indigestible food, this turns chyme into a semi solid
2. ) Temporary Storage - can temporarily store faeces in the transverse/descending colon
3. ) Fermentation - produces short chain FAs
   - majority of nutrients dont come from blood
   - FAs derived from fermentation of dietary fibre
   - by-products are CO2, methane, hydrogen gas
4. ) Microbiome - contains lots of commensal bacteria
   - microbes important for synthesis of certain vitamins (vitamin K)

Question 3

3 features of the blood supply to the large intestines

Midgut Arterial Supply
Hindgut Arterial Supply
Venous Drainage

Answer 3

1. ) Midgut Component - superior mesenteric artery (L1)
   - caecum/appendix –> 2/3 along tranverse colon
   - ileocolic supplies the caecum
   - right colic supplies the ascending colon
   - middle colic supplies the transverse colon (2/3)
2. ) Hindgut Component - inferior mesenteric artery (L3)
   - 2/3 transverse colon –> 1/3 rectum
   - left colic supplies the descending colon
   - sigmoid supplies the sigmoid colon
   - superior rectal (IMA continuation) supplies the rectum
3. ) Venous Drainage
   - midgut drains into the superior mesenteric vein
   - hindgut drains into the inferior mesenteric vein
   - upper 1/3 of rectum into the superior rectal vein (IMV)
   - lower 2/3 of rectum drains into systemic venous system (site of portosystemic anastomosis)

Question 4

3 features of water absorption in the large intestines

Volume of Water
Ion Channels x4
Tight Junctions

Answer 4

1. ) Volume of Water
   - approx 1500 ml of water enter the colon every day
   - most absorption occurs in the proximal colon
2. ) Ion Channels
   - ENaC (aldosterone induced) on the apical membrane allows Na+ influx which is followed by water molecules
   - K+ efflux channels also on apical membrane to maintain the electrical gradient
   - Na-K ATPase on the basolateral membrane
   - K+ efflux channels also on basolateral membrane
3. ) Tighter Tight Junctions
   - allows bigger diffusion gradients
   - less back diffusion of ions

Question 5

Diagnosis of Crohn’s disease

Risk Factors x2
Signs and Symptoms x4
Examination x2
Investigations x 4

Answer 5

1.) Risk Factors - young adult, smoker

2. ) Signs and Symptoms
   - loose, non-bloody stools
   - weight loss/malnutrition: reduced appetite and affects the SI so affects absorption
   - RLQ pain: terminal ileum most commonly affected
   - joint pain: extra-intestinal problems
3. ) Examination
   - tender mass in RLQ
   - mild perianal inflammation/ulceration
4. ) Investigations
   - colonoscopy: gross pathological changes
   - CT/MRI: bowel wall thickening, obstruction
   - bloods: anaemia
   - barium enema: strictures and fistulas

Question 6

6 pathological features of Crohn’s disease

Skip Lesions
Transmural Inflammation
Ulceration
Hyperaemia
Gross Appearance
Microscopic Feature

Answer 6

1. ) Skip Lesions - can affect anywhere in the GI tract but can skip areas of the bowel
   - terminal ileum involved in most cases
   - rarely affects the rectum
2. ) Transmural Inflammation - extends to the bowel wall
   - thickening of bowel wall and narrowing lumen
   - leads to fistulas between bowel and nearby structures
3. ) Ulceration - discrete superficial ulcers aswell as deeper ulcers
4. ) Hyperaemia - bowel is red/inflammed
5. ) Gross Apperance - cobblestone appearance in severe cases
6. ) Microscopic Feature - granuloma formation
   - see pathological processes

Question 7

Diagnosis of ulcerative colitis

Risk Factors x2
Signs and Symptoms x4
Examination x3
Investigations x5

Answer 7

1.) Risk Factors - young adult, female

2. ) Signs and Symptoms
   - bloody stools w/ mucus: loss of mucosal layers
   - weight loss: reduced appetite
   - lower abdominal pain: not speficially RLQ
   - painful red eye: extra-intestinal problems
3. ) Examination
   - mildly tender abdomen
   - no perianal disease
   - normal temperature
4. ) Investigations
   - colonoscopy: looking for gross pathology
   - stool cultures: looking for frank blood or mucous
   - bloods: anaemia
   - barium enema: mild cases only
   - CT/MRI - only mucosa affected so less useful

Question 8

6 pathological features in ulcerative colitis

Continous Lesions
Mucosal Inflammation
Haustra
Goblet Cells
Crypts
Pseudopolys

Answer 8

1. ) Continous Lesions - begins in the rectum and works its way up the GI tract
   - pancolitis is when the entire colon is affected (rare)
2. ) Mucosal Inflammation - it is shallow so doesn’t affect the bowel wall and stays in the mucosal membranes
   - mucosa is friable (touching it makes it bleed)
3. ) Loss of Haustra - inflammation reduces the appearance of haustra on imaging
4. ) Reduced Number of Goblet Cells
5. ) Crypt Distortion and Abscesses
   - irregular shaped glands w/ dysplasia
   - neutrophilic exudate in crypts (abscess)
6. ) Pseudopolyps - develop after repeated episodes
   - inflammation then healing

Question 9

2 treatment options of inflammatory bowel diseases

Medical
Surgical

Answer 9

1. ) Medical - steroids to reduce inflammation
   - e.g. corticosteroid or immunomodulators
2. ) Surgical
   - Crohn’s: not curative, remove small pieces of bowel each time, multiple surgeries leads to adhesions
   - UC: curable by doing a colectomy

Question 10

4 extra-intestinal problems in inflammatory bowel diseases

MSK
Skin
Liver/Biliary Tree
Eye Problems

Answer 10

1. ) MSK Pain (up to 50%)
   - arthritis (large joints) or nail clubbing
2. ) Skin Problems (up to 30%)
   - psoriasis, erythema nodosum, pyoderma gangrenosum

3.) Hepatobiliary - e.g. primary sclerosing cholangitis

4. ) Eye Problems (up to 5%) - e.g. painful red eye
   - episcleritis, anterior uveitis, or iritis

Question 11

Irritable Bowel Syndrome

Diagnosis
Stool symptoms
Other Symptoms
Investigations
Management
Dietary Advice

Answer 11

Diagnosis - diagnosis of exclusion (rule out everything else)
- abdominal pain/bloating/change in bowel habits for >6 months

Stool Symptoms

• change in stools or frequency
• symptoms worse on ingestion, relieved by defaecation
• altered stool passage, mucus in stools

Other Symptoms

• lethargy, back pain, headaches, nausea
• bladder complained, dysparaeunia, faecal soiling

Investigations

• FBC (anaemia), ESR/CRP (inflammation), coeliacs
• further imaging if required

Management

• antispasmodics, loperamide for diarrhoea, TCAs for abdo pain
• CBT, hypnotherapy

Dietary Advice

• regular meals, increase intake of water oats and linseed
• restrict carbonated drinks, fruits, artificial sweeteners (fructose)