Partial gastrectomy, the surgical removal of a portion of the stomach often performed to address gastric tumors or ulcers, can lead to the development of anemia in patients despite adequate dietary intake. The anemia observed post-surgery is generally due to malabsorption arising from the altered gastric physiology.

Causes of Anemia After Partial Gastrectomy

Several physiological changes occur after partial gastrectomy that contribute to anemia:

1. Reduced Gastric Acid Secretion and Iron Absorption

• Reduced Acid (HCl) Secretion:
  The stomach’s parietal cells produce hydrochloric acid, crucial for maintaining an acidic environment. After partial gastrectomy, the secretion of gastric acid decreases substantially.

• Impact on Iron Absorption:
  Acidic conditions in the stomach are essential to convert dietary ferric iron (Fe3+) into the more absorbable ferrous form (Fe2+). Reduced acid secretion impairs this conversion and, consequently, decreases the absorption of non-heme iron in the duodenum and proximal jejunum, leading to iron deficiency anemia.

2. Decreased Intrinsic Factor Secretion and Vitamin B12 Absorption

• Intrinsic Factor:
  Secreted by parietal cells, intrinsic factor is a glycoprotein essential for vitamin B12 absorption in the terminal ileum.

• Effect of Gastrectomy:
  Partial removal of the stomach reduces the number of parietal cells, decreasing intrinsic factor availability. This deficiency hampers vitamin B12 absorption, resulting in megaloblastic anemia (pernicious anemia).

3. Other Factors

• Folic Acid Absorption:
  While folic acid absorption primarily occurs in the proximal small intestine, its absorption is not directly influenced by gastric secretions. Hence, lower gastric acid does not significantly inhibit folic acid absorption.

• Protein Digestion:
  Partial gastrectomy may affect protein digestion to some extent due to altered gastric enzyme secretion but is generally not a direct cause of anemia.

Evaluating the Provided Explanations

• A. Lower gastric secretion inhibits folic acid absorption: Incorrect. Folic acid absorption is not markedly affected by gastric acid.

• B. Protein digestion was disturbed in partial gastrectomy: While partially true, it is not a primary cause of anemia.

• C. Lower HCl secretion from stomach reduced iron absorption: Correct. Reduction in stomach acid decreases iron absorption, causing iron deficiency anemia.

• D. Lower secretion of intrinsic protein factor from stomach reduced VitB absorption: Correct. Decreased intrinsic factor impairs vitamin B12 absorption, leading to megaloblastic anemia.

Summary Table of Anemia Causes Post-Gastrectomy

Conclusion

Among the possible explanations, the causes of anemia after partial gastrectomy best correspond to:
C. Lower HCl secretion reduces iron absorption
D. Lower intrinsic factor secretion reduces vitamin B12 absorption

Therefore, the correct answer is:
(3) C and D