Layers of GI Tract
- Epithelium.
- Lamina Propria.
- Muscularis Mucosae.
- Sub mucosa
- Muscularis Propria.
- Serosa/Adventitia.
- Inner circular muscle. Outer longitudinal. Myenteric/Auerbachs plexus is between two layers.
- Intraperitoneal // Ascend/Descend colon.
Histology of Small Intestine
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.
Histology of Large Intestine
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.
Diseases of Small Intestine
- Luminal
- Mucosal
- Post Mucosal
- Infections & bacterial overgrowth.
- Decrease SA.
Degradation of absorptive SA. - Lymphangiectasia
- Luminal Diseases
Small intestine
infections vs Bacterial overgrowth
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)
- Mucosal Diseases
Coeliac Disease
Small intestine
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.
- Post Mucosal Disease
Small intestine
Lymphangiectasia (Waldmans Disease).
Dilation of lymph vessels > ↑ protein loss.
Crohn’s Disease
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.
Ulcerative Colitis
Limited to large intestine + rectum. Extends only into mucosa + submucosa.
Idiopathic barrier dysfunction.
Other causes of Malabsorption
- Biliary Disease:
* Obstructed biliary drainage
- Intrahepatic
- Extrahepatic
* ADEK malabsorption
- Coagulopathy
- Osteomalacia
- Ataxia
- Night blindness - Pancreatic Disease:
- Chronic pancreatitis (alcohol)
- Tumours (duct obstruction/Zollinger-Ellison syndrome (Too much gastric acid)).
-
IBD Treatment
Monotherapy for flares:
Budesonide (steroid).
5-ASA (sulfazine/Mesalazine).
Maintance Crohns:
Methotrexate.
Azathioprine.
Maintance UC:
5-ASA.
Extra Intestinal complications of IBD
Extra manifestations
Arthritis.
Erythema Nodosum (on shins).
Pyoderma Gangrenosum (lower limbs).
Sclerosing Cholangitis.
Aphthous stomatitis (mouth ulcers ass. w/ Crohns).
