GI 1: Digestion And Absorption: Stomach

Question 0

HCL
What is its function?
We’re is it secreted?

Answer 0

Function:

• denatures proteins, making them more susceptible to degradation (increased surface area)
• activates enzymes: pepsinogen(inactive) ➡ pepsin (active)
• kills bacteria

Secreted by parietal cells
-parietal cells obtain chloride from interstitial fluid in exchange for bicarbonate (which is produced from carbon dioxide and water via carbonic acid)

Question 1

Gastric fluids comprise of?

Answer 1

HCL
Proteolytic enzyme
Mucus 
Intrinsic factor 
Lipase

Question 2

Digestive enzymes: pepsin (protease)
Secreted by?
Function?

Answer 2

Secreted by chief cells into stomach lumen
-activated by H+ and pepsin
Pepsin ➡➡➡➡(H+)➡➡➡ pepsin + peptide
-acts on peptide bonds (only partial digestion of proteins occurs in the stomach)

Question 3

Digestive enzymes: lipases
Secreted by?
Function?

Answer 3

• secreted in saliva and stomach
• most important source of lipase in adults is pancreas (pancreatic secretions into small intestine)
• gastric lipase is secreted by parietal cells

Gastric lipase is most important in young animals, limited activity in adults because pH is too low (acidic) in gastric fluid
-very active on milk TAG

Question 4

Intrinsic factor
Secreted by?
Function?

Answer 4

• secreted by parietal cells

- glycoprotein➡ specifically binds to vitamin B12 making it less susceptible to proteolysis

Question 5

Mucus
Secreted by?
Function?

Answer 5

-secreted by mucus cells 
Function: 
-protects epithelial lining from enzymatic attack 
-lines and lubricates GI tract
-resistant t proteolysis

Question 6

Digestion in stomach of young mammals.

Describe the role of the stomach for colostrum and milk digestion in neonates?

Answer 6

High consumption of milk:

• major milk protein is casein
• casein + renin (protease) ➡ milk clot
• renin is the most active for first few days then is replaced by pepsin

Clotting slows down passage of milk through GIT

• this promotes greater enzymatic digestion and absorption of nutrients
• many milk replacers don’t clot ➡ diarrhoea

Amount of casein determines clot formation and suckling frequency
-humans has low casein➡ less milk clotting ➡ increased suckling frequency relative to calves

This clot is slowly dissolved by digestive enzymes

• lactose is digested in small intestine
• in calves the slow release of these provides constant supply of nutrients over 10 hours
• in humans the clot is less rigid due to lower casein content ➡ less time in stomach ➡ more digestion of milk occurs in small intestine

Parietal cells (HCL, gastric lipase, intrinsic factor) have minimal activity immediately after birth

• stomach has high pH and low protease activity
• this allows y-globins (colostrum) to reach small intestine in tact to be absorbed ➡ important antibodies need to be absorbed here