The systemic and pulmonary circulations are quite different in several respects (Table 7.00). The systemic circulation serves many tissues, thus it has variable requirements and exerts many controls. Due to the high vascular resistance, substantial perfusion pressure is required and long hydrostatic columns are involved, in some cases from the head to the toes. In contrast, the pulmonary circulation serves only one organ; thus, it has essentially a single function, gas exchange. There is little control of this circulation (not none) as compared to the systemic circulation. Since the lung is all located near the heart, short hydrostatic columns are involved, and low resistance is encountered, thus requiring low perfusion pressure.
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