Erythropoiesis - Pernicious Anemia

Question 1

What causes pernicious anemia?

Answer 1

Failure to absorb Vitamin B12 from the gastrointestinal tract.

Question 2

What is the basic abnormality of pernicious anemia?

Answer 2

Atrophic gastric mucosa that fails to produce normal gastric secretions.

Question 3

What is intrinsic factor?

Answer 3

A glycoprotein secreted by the parietal cells of the gastric glands.

Question 4

How does intrinsic factor facilitate the absorption of vitamin B12 by the gut?

Answer 4

1. It binds tightly with vit. B12 and protects it from digestion by GI secretions.
2. In the bound state, intrinsic factor binds to specific receptor sites on the brush border membranes of the mucosal cells in the ileum.
3. Vit. B12 is transported into blood during the next few hours by process of pinocytosis, carrying the intrinsic factor and the vitamin together through the membrane.

Question 5

Why does lack of intrinsic factor cause a decrease in the availability of vitamin B12?

Answer 5

Due to the faulty absorption of vit. B12.

Question 6

What happens after vit. B12 is absorbed from the gastrointestinal tract?

Answer 6

First stored in large quantities in the liver.

Then released slowly as needed by the bone marrow.

Question 7

What is the minimum amount of vit. B12 required each day to maintain normal RBC maturation?

How many years of defective vit. B12 absorption are usually required to cause maturation failure anemia?

Answer 7

1-3 micrograms

(normal storage in liver and other body tissues is about 1000 times this amount)

3 to 4 years.