Question

1. A genetic inability to produce intrinsic factor affects what cells? And leads to a deficiency of what nutrient? Why?

2. Compare/contrast the roles of HCl and Bile.

Answer 1

1. Intrinsic factor is a glycoprotein that is produced by the parietal cells of the stomach, which also produce HCl. Intrinsic factor is required for absorption of vitamin B12 by the small intestine. Receptors for intrinsic factor are expressed on mucosal cells of the small intestinal ileum.

Intrinsic factor (IF) binds to vitamin B12 or cobalamin in the duodenum. This IF will then binds to cubam receptors on the ileum mucosa and allow vitamin B12 to be absorbed. The vitamin B12-IF is then taken in by the enterocytes via receptor mediated endocytosis. IF is then cleaved from vitamin B12 by lysosomal enzymes, from where it is transported to plasma membrane and target tissues. Hence, deficiency of IF causes malabsorption of vitamin B12 in small intestine. This affects red blood cell maturation leading to pernicious anemia.

2.

HCl	Bile
Hydrochloric acid is produced by the parietal cells of the stomach.	Bile is produced by the liver by hepatocytes.
HCl is acidic and lowers the pH of stomach.	Bile is alkaline as it contains bile acids, pigments, cholesterol and lecithin.
HCl acts in the stomach, and is required to convert pepsinogen to pepsin.	Bile is carried to the gall bladder by bile ducts. Bile is released in the small intestine, where it causes emulsification of fat. It is also required for transport of triglycerides to the enterocytes. It is also required for absorption of fat soluble vitamins.
Its main function is to activate pepsin for protein digestion.	It is required for enhancing lipase action for breakdown of lipids.
Gastrin is responsible for secretion of HCl in stomach.	Secretion of bile into small intestine from gall bladder occurs in response to secretin.
It is a single molecule.	It is made up of different components- bile acids, pigments, cholesterol and lecithin.
Bile can be regurgitated into stomach, where it is neutralizes HCl. HCl does not neutralize bile.	Bile will neutralize any HCl that enters the small intestine.
HCL has no action of bilirubin.	Bile is required for excretion of bilirubin, a breakdown product of red blood cells. Toxic compound such as copper, zinc and mercury are excreted through bile.

Comparison:

1. Both bile and hydrochloric acid (HCl are required for digestion.

2. Secretion of both bile and HCl are under control of hormones.

3. Both bile and HCl cause destruction of any foodborne bacteria that enter the small intestine or stomach.

4. Both maintain the pH of the organs they act on.