The Heart Pumps Blood, Not the Lungs: Circulatory System Basics
The heart is the pump; the lungs are the gas exchanger. This distinction is fundamental to cardiovascular physiology.
Circulatory Pathway
- Right heart: RA → RV → Pulmonary artery → Lungs (O₂ uptake, CO₂ release).
- Left heart: LA → LV → Aorta → Systemic arteries → Capillaries (O₂ delivery, CO₂ pickup) → Veins → RA.
Why the Lungs Don't Pump
- Pulmonary circulation is low pressure (mean PAP 15 mmHg vs. systemic MAP 90 mmHg).
- Lungs lack contractile tissue; flow driven by RV pressure.
- Lung vessels are thin-walled, distensible, and highly compliant for gas exchange.
Heart as Dual Pump
- Right ventricle: Volume pump (thin wall, crescent shape).
- Left ventricle: Pressure pump (thick wall, circular).
- Both eject same volume (≈70 mL/beat) in series.
Clinical Correlate
Right heart failure (cor pulmonale) from lung disease (COPD, PE) → RV dilation → tricuspid regurgitation → systemic venous congestion. Left heart failure → pulmonary venous hypertension → pulmonary edema.
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