Week 1

Question 1

Layers of GI Tract

Answer 1

1. Epithelium.
2. Lamina Propria.
3. Muscularis Mucosae.
4. Sub mucosa
5. Muscularis Propria.
6. Serosa/Adventitia.

5. Inner circular muscle. Outer longitudinal. Myenteric/Auerbachs plexus is between two layers.
6. Intraperitoneal // Ascend/Descend colon.

Question 2

Histology of Small Intestine

Answer 2

Columnar Epithelium (goblet + enterocytes (absorptive)).
Paneth Cells- Base of crypts. Secrete eosinophilic lysozyme-rich granules (anti microbial peptides) to regulate flora.
Brunner’s Gland (prox. duodenum submucosa).
Peyer’s Patches (lymphoid tissue).

Brunners secretes alkaline fluid (+ mucin) to protect mucosa from acidic stomach contents.

Question 3

Histology of Large Intestine

Answer 3

Simple Columnar Epithelium.
Smooth surface - Crypts (test tube shape, equal spacing).
- Goblet cells
- Absorptive coloncytes
- Endocrine cells
- Paneth cells ( R colon).

Absorptive coloncytes - absorb water back into system.

Question 4

Diseases of Small Intestine

Answer 4

1. Luminal
2. Mucosal
3. Post Mucosal

1. Infections & bacterial overgrowth.
2. Decrease SA.
   Degradation of absorptive SA.
3. Lymphangiectasia

Question 5

1. Luminal Diseases

Small intestine

infections vs Bacterial overgrowth

Answer 5

Infections:
* Giardiasis (bloating + steatorrhea)
* TB
* Ancylcostoma (round worm)
* Tropheryma Whippelii (villious atrophy)
* Cryptosporidium/microsporidium/isopera associated with AIDS

Bacterial overgrowth:
* High folate, low B12
* Jejunal diverticulosis
* Blind loop syndrome
* Motility disorders (diabetes/scleroderma)

Question 6

2. Mucosal Diseases

Coeliac Disease

Small intestine

Answer 6

Type 4 HS.
Gluten enteropathy.
Subtotal villous atrophy.
Crypt hyperplasia.
Auto antibodies - Anti Tissue transglutaminase (Endomysial antibodies).
HLA-DQ2 - 90%
HLA-DQ8 - (10%)

Fe & Folate Deficiency + osteomalacia (vit D def)

Terminal ileal surgery results in bile salt & B12 malabsorption - resulting in megaloblastic anaemia, dementia, optic atrophy.

Question 7

3. Post Mucosal Disease

Small intestine

Answer 7

Lymphangiectasia (Waldmans Disease).
Dilation of lymph vessels > ↑ protein loss.

Question 8

Crohn’s Disease

Answer 8

Aka regional enteritis.
Skip lesions/Aphthous Ulcer.
Cobble stone appearance.
Noncaseating granulomas (hallmark of Crohns)

Can affect anywhere but common: terminal ileum, ileocecal valve, cecum.

path:
1. NOD2 mutation: activation of NF-κB > overstimulation of immune system.
- ATG16L1 (Autophagy related 16-like-1) and IRGM (immune related GTPase M).
2. Mucosal immune response: Polymorphorism in IL-23 confer protection against CD and UC.
Defects in Treg (IL-10 producing) result in severe/early onset colitis.
3. Epithelial defects: defects in intestinal epithelial tight functions in CD.

Question 9

Ulcerative Colitis

Answer 9

Limited to large intestine + rectum. Extends only into mucosa + submucosa.
Idiopathic barrier dysfunction.

Question 10

Other causes of Malabsorption

Answer 10

1. Biliary Disease:
   * Obstructed biliary drainage
   - Intrahepatic
   - Extrahepatic
   * ADEK malabsorption
   - Coagulopathy
   - Osteomalacia
   - Ataxia
   - Night blindness
2. Pancreatic Disease:
   - Chronic pancreatitis (alcohol)
   - Tumours (duct obstruction/Zollinger-Ellison syndrome (Too much gastric acid)).
   -

Question 11

IBD Treatment

Answer 11

Monotherapy for flares:
Budesonide (steroid).
5-ASA (sulfazine/Mesalazine).

Maintance Crohns:
Methotrexate.
Azathioprine.
Maintance UC:
5-ASA.

Question 12

Extra Intestinal complications of IBD

Extra manifestations

Answer 12

Arthritis.
Erythema Nodosum (on shins).
Pyoderma Gangrenosum (lower limbs).
Sclerosing Cholangitis.
Aphthous stomatitis (mouth ulcers ass. w/ Crohns).