Introduction

At high altitude, low oxygen availability (hypoxia) triggers adaptive responses to improve oxygen delivery, including increased red blood cell (RBC) production. Understanding these compensatory mechanisms is essential for appreciating acclimatization and managing altitude sickness. This article evaluates four proposed changes related to RBC production during high-altitude hypoxia and identifies which is not true.

Analysis of Statements

A. The transcription factors, HIFs, are produced.

• True.
  Hypoxia-inducible factors (HIFs) are key transcription regulators in the cellular response to low oxygen. They promote erythropoietin (EPO) gene expression, which in turn stimulates RBC production.

B. Erythropoietin secretion is increased.

• True.
  EPO secretion by the kidneys increases in response to hypoxia-mediated HIF activation. Elevated EPO stimulates bone marrow to produce more RBCs, increasing oxygen transport capacity.

C. Myoglobin content is decreased.

• False.
  Myoglobin content in muscle typically increases or remains stable to enhance oxygen storage and facilitate oxygen diffusion during hypoxia. Decrease in myoglobin is not an adaptive response to hypoxia.

D. Cytochrome oxidase is decreased.

• False.
  Cytochrome oxidase (complex IV of the electron transport chain) generally increases or its activity is maintained to optimize mitochondrial respiration under hypoxic conditions. A decrease is not characteristic of acclimatization.

Summary Table

Identifying the Incorrect Statements Combination

• The incorrect statements are C and D.

Conclusion

The option containing both incorrect statements about RBC changes during high altitude acclimatization is:

(4) C and D