Heart and Lungs: The Cardiopulmonary Partnership

How the Heart and Lungs Collaborate

The cardiovascular and respiratory systems form a unified circuit delivering O₂ to tissues and removing CO₂.

1. Pulmonary Circulation (Right Heart → Lungs → Left Heart)

1. Deoxygenated blood enters right atrium via superior/inferior vena cava.
2. Flows through tricuspid valve to right ventricle.
3. RV contracts → blood ejected through pulmonary valve into pulmonary arteries.
4. In pulmonary capillaries, CO₂ diffuses out, O₂ diffuses in (gas exchange).
5. Oxygenated blood returns via pulmonary veins to left atrium.

2. Systemic Circulation (Left Heart → Body → Right Heart)

1. Blood passes mitral valve to left ventricle.
2. LV contracts → blood ejected through aortic valve into aorta.
3. Arteries → arterioles → systemic capillaries: O₂ delivered to cells, CO₂ picked up.
4. Deoxygenated blood returns via veins to vena cavae → right atrium.

Continuous Coordination

• Frank-Starling law: RV and LV outputs match beat-to-beat.
• Ventilation-perfusion matching: Local hypoxic vasoconstriction directs blood to well-ventilated alveoli.
• Chemoreflexes: Carotid/aortic bodies sense PO₂, PCO₂, pH → adjust breathing and heart rate.

Clinical Integration

Heart failure → pulmonary edema (impaired LV emptying). Lung disease (COPD) → pulmonary hypertension → right heart failure (cor pulmonale). Treating one organ often benefits the other.