In atrophic gastritis with macrocytic anemia, which gastric cell type is absent?

• A. Parietal cells
• B. Chief cells
• C. Mucous cells
• D. G cells

Answer: (A)

Autoimmune destruction of the acid-secreting parietal cells in the stomach's fundic glands is the key event. Parietal cells produce gastric acid and intrinsic factor, and intrinsic factor is essential for vitamin B12 absorption from the gut. When these cells are lost, intrinsic factor falls, B12 cannot be absorbed effectively, and over time you develop pernicious anemia with a macrocytic (megaloblastic) blood picture due to impaired DNA synthesis in hematopoietic cells. The loss of parietal cells also explains the low acid state. Other gastric cell types, like mucous-secreting cells and G cells, aren’t the primary targets of this autoimmune process, so they’re not characteristically absent.