What is the mechanism of megaloblastic anemia?

Megaloblastic anemia results from inhibition of DNA synthesis during red blood cell production. When DNA synthesis is impaired, the cell cycle cannot progress from the G2 growth stage to the mitosis (M) stage. This leads to continuing cell growth without division, which presents as macrocytosis.

What are the two main causes types of megaloblastic anemia?

The two most common causes of megaloblastic anemia are deficiencies of vitamin B12 and folate. These two nutrients are necessary for producing healthy RBCs.

Is megaloblastic anemia acquired?

Usually, megaloblastic anemia is due to acquired deficiency in vitamin B12 or folic acid. The deficiency can be related to inadequate dietary intake of these B vitamins or poor intestinal absorption.

What is the mechanism of pernicious anemia?

Pernicious anemia (PA) is megaloblastic anemia resulting from a deficiency of cobalamin (vitamin B12), which in turn is caused by a lack of intrinsic factor (IF). Intrinsic factor is a glycoprotein that binds cobalamin and thereby enables its absorption in the terminal ileum.

Which of the following steps of vitamin B12 absorption occur in the stomach?

In the small intestine, vitamin B-12 binds with intrinsic factor, which is made in the stomach.

Why does MCV increase in megaloblastic anemia?

These large polychromatophilic erythrocytes noted on the peripheral smear represent reticulocytes, immature RBCs that are larger than mature RBCs, and are indicative of increased erythropoiesis or RBC production and, if present in increased number, can raise the MCV.

Why does MCH increase in megaloblastic anemia?

Defects in nuclear maturation, as seen in megaloblastic anemias due to folate or B12 deficiency, result in large oval erythrocytes (macroovalocytes) with a normal hemoglobin content. The MCV and MCH are increased, while the MCHC remains normal.

Why does gastrin increase in pernicious anemia?

Those with pernicious anemia are at increased risk for gastric carcinoid tumors, and adenocarcinoma, due to hypochlorhydria. The hypochlorhydria associated with pernicious anemia induces hyperplasia of the G cells (the cell type responsible for producing gastrin) and hypergastrinemia.