Pulmonary vs. Systemic Circulation Pressure

Steps:

• Identify the two circulations: pulmonary (lungs) from right ventricle, systemic (body) from left ventricle.
• Recall that pulmonary circulation requires low pressure to protect thin alveolar walls for gas exchange.
• Compare pressures: pulmonary artery ~25/10 mmHg, systemic aorta ~120/80 mmHg.
• Confirm the key difference is pressure, not distance, speed, or volume.

Why A is correct:

• Pulmonary circulation operates at lower pressure (mean ~15 mmHg) per the physiology of gas exchange, preventing damage to delicate lung capillaries, as defined by cardiovascular hemodynamics.

Why the others are wrong:

• B: Pulmonary path is shorter (heart to lungs) than systemic (whole body).
• C: Blood velocity is similar or slightly higher in lungs due to vessel diameter, not a defining difference.
• D: Blood volume flow (cardiac output) is equal in both circuits (~5 L/min).

Final answer: A