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Why is blood pressure lower in the pulmonary circulation than in the systemic circulation?

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Illustration of a human heart cross-section showing four chambers-left and right atria and ventricles-with labeled major blood vessels. An inset highlights cardiac muscle tissue, showing myocytes and intercalated disks. — human cardiovascular system The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.

Blood pressure is significantly lower in the pulmonary circulation than in the systemic circulation primarily to protect the delicate tissues of the lungs during gas exchange.1

The systemic circuit is much longer and requires higher pressure to distribute blood throughout the entire body, a task performed by the thick, muscular wall of the left ventricle. In contrast, the pulmonary circuit is shorter and serves only the lungs; operating at lower pressures allows for efficient gas exchange without causing damage to the alveolar capillary networks. Because of these differing functional requirements, the pulmonary arteries are structurally thinner and more flimsy than the systemic arteries, which must withstand much higher internal pressures. In humans, the pressure within the aorta is approximately six times higher than that found in the pulmonary artery.213