Learning Objective

Describe the structure, function, lifespan, metabolism, and clinical features of erythrocytes, including reticulocytes and common morphological terms.

Erythrocytes (Red Blood Cells, RBCs)

Structure

• Anucleate and lack organelles.
• Biconcave shape → increases surface area-to-volume ratio for rapid gas exchange.
• Diameter ~7–8 µm; flexible to pass through microvasculature.

Function

• Carry O₂ from lungs to tissues.
• Carry CO₂ from tissues to lungs (via Cl⁻/HCO₃⁻ antiporter in RBC membrane).
• Export HCO₃⁻ to facilitate CO₂ transport to the lungs.

Lifespan

• Healthy adults: ~120 days.
• Neonates: 60–90 days.

Activity

Metabolism

• Glucose is the primary energy source:
  • 90% via glycolysis → ATP for membrane integrity and ion pumps.
  • 10% via hexose monophosphate (HMP) shunt → generates NADPH for protection against oxidative stress.

Clinical and Laboratory Terms

• Erythrocytosis / Polycythemia: Increased hematocrit (Hct).
• Anisocytosis: RBCs of varying sizes.
• Poikilocytosis: RBCs of varying shapes.
• Reticulocyte: Immature RBC; reflects erythroid proliferation.
  • Polychromasia (bluish staining) on Wright-Giemsa → residual ribosomal RNA.

Activity