GI Tract (incl. CRC)

Question 1

What are the 3 main cell types found in the colon?

Answer 1

> Goblet
Columnar
Endocrine

All derived from the same pluripotent stem cell

Question 2

What are the two common pre-cancerous lesions found in the colon?

Answer 2

> Hereditary Non-Polyposis Colorectal
Autosomal dominant genetic condition affecting DNA damage repair ability

> Familial Adenomatous Polyposis
Autosomal dominant APC mutation, leading to over-activation of the canonical WNT pathway (via increased beta-catenin) and hyperproliferation, leading to numerous polyp formations

Question 3

What lifestyle factors affect CRC risk?

Answer 3

CRC risk is closely linked to diet. Fish & fibre decrease risk, whereas red meat consumption increases risk.

Question 4

What tissue type does colorectal cancer mainly affect?

Answer 4

Glandular tissue (adenomas/adenocarcinomas)

Question 5

What role does WNT signalling play in CRC?

Answer 5

Disrupted WNT signalling (e.g. due to APC mutation leading to FAP) can cause hyperproliferative pre-cancerous lesions throughout the colon, increasing the risk of developing an invasive adenocarcinoma.

Question 6

What are the 4 layers that comprise the epithelium found throughout the GI tract?

Answer 6

1. Mucosal layer - Most epithelial, supports the lumen
2. Sub-mucosal layer - Collagenous tissue, supports mucosa
3. Muscularis Propria - Smooth muscle, involved in peristalsis
4. Adventitia - Supporting tissue

Question 7

What are the 4 mucosal types found throughout the GI tract?

Answer 7

1. Protective
2. Secretory
3. Absorptive
4. Absorptive/protective

Question 8

What is the most common pre-cancerous lesion affecting the oesophagus, and how does it present?

Answer 8

Barret’s Oesophagus

Metaplastic lesion on the oesophagus due to chronic acid reflux from the stomach. Metaplastic change of the normal squamous epithelium to columnar epithelium (which resembles small intestine/head of stomach). Chronic irritation/inflammation can lead to dysplasia, then carcinoma.

Question 9

What is the most common pre-cancerous lesion affecting affecting the stomach, and how does it present?

Answer 9

Chronic gastritis, often derived from Helicobater pylori infection

Helicobacter pylori colonise below the epithelium (below protective mucous). Induces a chronic inflammatory immune response, which increases the chance of metaplasia and finally dysplasia/neoplasia.

Question 10

What can cause acute gastritis?

Answer 10

Alcohol intake, NSAIDs use, bile reflux.

Question 11

There are four types of carcinoma of the stomach, what are they?

Answer 11

1. Polypoid - protrusion in to lumen
2. Fungating - an ulcerating polypoid
3. Ulcerated - lesion resembling a peptic ulcer
4. Infiltrative - diffuse spread of mucosa/submucosa

Question 12

What is the most common cause of malabsorption in the small intestine?

Answer 12

Coeliac Disease

Atrophy of the villi of the small intestine due to an immune response to GLIADIN, a glycoprotein found in gluten.

Question 13

There are two types of IBD - what are they, and how do they differ?

Answer 13

Crohn’s Disease - affects any part of GI, inflammation occurs across all layers, frequent remission/relapse.

Ulcerative Collitis - inflammatory disease of colorectal mucosa, extends across whole of colonic epithelium, mucosal infiltration of inflammatory cells.

Question 14

Is there any progression from IBD?

Answer 14

There is an increased risk of CRC occurring in patients with IBD - with 15% of deaths in patients with IBD caused by CRC.