Colorectal Cancer - Anatomy

Question 1

GI Tract Layers

Answer 1

• 1) Mucosa: Epithellum, Lamina Propria, Muscularis Mucosae (most inner)
• 2) Submucosa (contains glands)
• 3) Muscularis: circular muscle, longitudinal muscle
• 4) Serosa (outer)

Question 2

Large Intestine Anatomy

Answer 2

• Appendix is attached to the Cecum
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon, attaches to the rectum and the anal canal

Question 3

Haustral Churning

Answer 3

• In large intestine

- Haustral churning - relax and distend while filling up, when stretched they squeeze contents into next haustra

Question 4

Peristalsis

Answer 4

• Large intestine

- Occurs at a slower rate than movement in the rest of the GI tract

Question 5

Mass Peristalsis

Answer 5

• Strong peristaltic wave initiated by the intake of food

- Begins in transverse colon and drives contents into the rectum

Question 6

Digestion in the small intestine

Answer 6

• Carbohydrates: bacteria ferment carbs and release hydrogen, carbon dioxide and methanic gas
• Proteins: bacteria convert remaining proteins into amino acids and break them down further into simpler substances, Indole, Skatole, Hydrogen Sulfide and fatty acids
• Bilirubin: bacteria decompose into simpler pigments, giving faeces its brown colour

Question 7

Osmosis in the large intestine

Answer 7

• Most water is absorbed in small intestine, large intestine still absorbs a lot
• Passively, via sodium active transport
• Only about 100mL water reaches the rectum per day

Question 8

Defacation

Answer 8

• faeces: water, inorganic salts, sloughed off epithelial cells, undigested food, bile, mucus

Question 9

Peritoneum

Answer 9

• Covers stomach, small intestine, large intestine

Question 10

What is the histology of the layers of the GI tract?

Answer 10

• Absorptive and goblet cells are located in long, straight, tubular intestinal glands which extend the fyll thickness of the mucosa
• Lymphatic nodules may extend through the muscularis mucosae into the submucosa
• The submucosa is composed of areolar connective tissue.
• The muscularis consists of an external layer of longitudinal smooth muscle and an internal layer of smooth circular muscle