Red Blood Cell Circulation: Journey Through the Cardiovascular System

The Circuit

1. Right Heart – Deoxygenated RBCs enter right atrium → right ventricle.
2. Pulmonary Arteries – To lungs.
3. Pulmonary Capillaries – CO₂ offloaded, O₂ loaded (diffusion).
4. Pulmonary Veins – Oxygenated blood to left atrium.
5. Left Heart – Left atrium → left ventricle.
6. Aorta → Arteries → Arterioles – Distribution.
7. Systemic Capillaries – O₂ delivered to tissues; CO₂ picked up.
8. Venules → Veins → Vena Cava – Return to right heart.

RBC Adaptations

• Biconcave disc → high surface area/volume.
• Deformable (no nucleus) → squeezes through 3–4 µm capillaries.
• Hemoglobin (270M/cell) – carries 4 O₂ each.
• 120-day lifespan; recycled in spleen/liver.

Continuous Flow

~5 L blood circulates ~1 minute at rest. 25 trillion RBCs make ~250,000 trips in their lifetime.