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Structure and function of the pulmonary circulation 

Structure and function of the pulmonary circulation
Structure and function of the pulmonary circulation

Nicholas W. Morrell

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date: 05 March 2021

The normal pulmonary circulation distributes deoxygenated blood at low pressure and high flow to the pulmonary capillaries for the purposes of gas exchange. The structure of pulmonary blood vessels varies with their function—from large elastic conductance arteries, to small muscular arteries, to thin-walled vessels involved in gas exchange.

Pulmonary vascular resistance is about one-tenth of systemic vascular resistance, with the small muscular and partially muscular arteries of 50–150 µm diameter being the site of the greatest contribution to resistance. In the normal pulmonary circulation, a large increase in cardiac output causes only a small rise in mean pulmonary arterial pressure because pulmonary vascular resistance falls on exercise. Pulmonary blood flow is heterogeneous: gravity causes increased blood flow in the more dependent parts of the lung; within a horizontal region—or within an acinus—blood-flow heterogeneity is imposed by the branching pattern of the vessels.

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