Capillary blood flow

At any given moment, not all capillaries supplied by a single metarteriole are perfused simultaneously. Similarly, blood flow is not continuous in any given capillary. Thus capillary blood flow is intermittent, with alternating periods of perfusion and periods of collapse every few minutes. This intermittence in capillary blood flow is caused by a phenomenon called vasomotion which is due to intermittent contraction of the metarteriole and of the pre-capillary sphincter.

Despite the intermittence of capillary blood flow, considering the enormous number of capillaries in certain tissues, the function of the capillary network can be assessed by a mean value. Thus mean values of capillary output, capillary pressure and substance transfer through the capillary wall can be determined.

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