Macrocytic Anaemia and Its Causes

Questions and Answers

What is the reactive center of the vitamin B12 molecule attached to in cyanocobalamin?

Cyano group (-CN)

How is vitamin B12 mainly combined in the stomach for absorption?

With glycoprotein intrinsic factor (IF)

What directs the endocytosis of the cubilin IF–B12 complex into the ileal cell for absorption?

Amnionless proteins

Which protein is responsible for releasing dietary B12 for binding to intrinsic factor (IF) in the stomach?

Haptocorrin Signup and view all the answers

What is the maximum amount of B 12 that can be absorbed from a single oral dose via the IF–cubam mechanism?

1–2 μg Signup and view all the answers

What is the characteristic abnormality seen in the bone marrow erythroblasts in megaloblastic anaemias?

Delayed maturation of the nucleus relative to the cytoplasm Signup and view all the answers

Which vitamin deficiency is most commonly associated with defective DNA synthesis causing megaloblastic anaemias?

Vitamin B12 Signup and view all the answers

What may cause an elevated MCV as an artefact reported by an automated cell counter in macrocytic anaemia?

Red cell agglutination Signup and view all the answers

What is the underlying defect responsible for the asynchronous maturation of the nucleus in megaloblastic anaemias?

Defective DNA synthesis Signup and view all the answers

Apart from vitamin deficiencies, what else may cause an identical haematological appearance to megaloblastic anaemias?

Abnormalities induced by drugs Signup and view all the answers

What is the main plasma-binding protein responsible for delivering Vitamin B12 to the bone marrow and other tissues?

Transcobalamin II (TC) Signup and view all the answers

Where does Vitamin B12 become attached to the plasma-binding protein transcobalamin (TC)?

Ileal cell Signup and view all the answers

What is the characteristic abnormality seen in the bone marrow erythroblasts in megaloblastic anemias?

Asynchronous maturation of the nucleus Signup and view all the answers

Study Notes

Vitamin B12 and Absorption

In cyanocobalamin, the reactive center of the vitamin B12 molecule is attached to a cyanide group.
Vitamin B12 is mainly combined with intrinsic factor (IF) in the stomach for absorption.
The cubilin receptor directs the endocytosis of the cubilin-IF-B12 complex into the ileal cell for absorption.

Vitamin B12 Release and Absorption

Gastric acid and pepsin release dietary B12 from food for binding to intrinsic factor (IF) in the stomach.
The maximum amount of B12 that can be absorbed from a single oral dose via the IF-cubam mechanism is 1.5-2.0 μg.

Megaloblastic Anemias

The characteristic abnormality seen in the bone marrow erythroblasts in megaloblastic anemias is asynchronous maturation of the nucleus.
Vitamin B12 deficiency is most commonly associated with defective DNA synthesis, causing megaloblastic anemias.
Apart from vitamin deficiencies, other conditions like inherited disorders of DNA synthesis may cause an identical hematological appearance to megaloblastic anemias.

Vitamin B12 Transport

The main plasma-binding protein responsible for delivering Vitamin B12 to the bone marrow and other tissues is transcobalamin (TC).
Vitamin B12 becomes attached to the plasma-binding protein transcobalamin (TC) in the ileal cells.

Macrocytic Anemia

In macrocytic anemia, an elevated MCV may be reported as an artefact by an automated cell counter due to the presence of cytoplasmic fragments or Howell-Jolly bodies.