Understanding Pulmonary Circulation: Blood Flow from Heart to Lungs

Pulmonary circulation carries deoxygenated blood from the right heart to the lungs for gas exchange and returns oxygenated blood to the left heart.

Pathway

1. Right ventricle → main pulmonary artery
2. Bifurcates → right & left pulmonary arteries
3. Lobar → segmental → subsegmental arteries → arterioles
4. Pulmonary capillary network surrounding alveoli
5. Gas exchange: CO₂ out, O₂ in (diffusion across alveolar-capillary membrane)
6. Oxygenated blood → pulmonary venules → 4 pulmonary veins → left atrium

Key Features

• Low pressure (~15 mmHg systolic), high compliance, low resistance.
• Recruits/distends vessels with increased flow (exercise).
• Hypoxic pulmonary vasoconstriction matches perfusion to ventilation.

Systemic Circulation (Contrast)

Left ventricle → aorta → arteries → arterioles → systemic capillaries (O₂ delivery, CO₂ pickup) → venules → venae cavae → right atrium. High pressure, high resistance.