Pulmonary Artery Anatomy: Deoxygenated Blood to Both Lungs

The pulmonary artery carries deoxygenated blood from the right ventricle to both lungs—not just the left lung. This is a fundamental principle of cardiopulmonary circulation.

Pulmonary Circulation Pathway

1. Right ventricle contracts
2. Pulmonary valve opens
3. Main pulmonary artery (trunk) → 5 cm long
4. Bifurcation at T4/T5 level:
   • Right pulmonary artery (RPA): Longer, wider; passes under aortic arch
   • Left pulmonary artery (LPA): Shorter; connects to ligamentum arteriosum
5. Branch into lobar, segmental, subsegmental arteries
6. Pulmonary capillaries (alveolar gas exchange)
7. Pulmonary veins (4) → left atrium (oxygenated blood)

Key Features

• Only artery carrying deoxygenated blood (fetal: umbilical arteries)
• Low pressure: Mean PAP 15 mmHg (vs. systemic 95 mmHg)
• Thin walls: Less smooth muscle, more compliance
• Distensible: Recruits capillaries during exercise

Clinical Relevance

• Pulmonary embolism: Thrombus lodges in pulmonary arteries → V/Q mismatch, right heart strain
• Pulmonary hypertension: Mean PAP >20 mmHg; WHO Groups 1-5
• Congenital: Pulmonary atresia, stenosis, anomalous origin
• Imaging: CT pulmonary angiography (CTPA) gold standard for PE
• Catheterization: Right heart cath measures pressures, calculates PVR

Common Misconception Correction

The original statement "transports blood to the left lungs" is anatomically incorrect. The pulmonary trunk bifurcates to supply both right and left lungs. Each lung receives approximately 55% (right) and 45% (left) of cardiac output, reflecting lung size difference.

Understanding bilateral pulmonary perfusion is essential for interpreting V/Q scans, planning lung resection, and managing pulmonary vascular disease.