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Zone of microcirculation

A structural unit of microcirculation zone is capillaron: arteriole, venule, A-V-anastomosis and up to 20 capillaries united by metarteriole. A blood flow covers arteriole, metarteriole and about 20% capillaries. Sphincters of other capillaries are closed there is no blood flow in them. As a signal to relaxation of capillary sphincters is accumulation of acidic products and histamine coming from the tissues.

The main function of capillaron is carrying out a correlation between demands of cells and their blood supply, i.e. a function of metabolism the constituent part of which is nutrition of tissues.

Since it is so, the walls of the true capillary (capillary membrane) do not contain muscular layer and consist of only one layer of endothelium.

By virtue of constant functional activity of capillary sphincters, a continuous inflow and outflow of blood occurs in the capillaries that got the name of vasomotion.

Endothelial capillary membranes consist of endothelial cells that in acidic media or in Ca⁺⁺ deficit start to disconnect, forming slits. These changes explain an increased permeability of capillary membrane. Endothelium has a tone to resist the strain. This tone is regulated by corticosteroids, and histamine, on the contrary, leads to a depression of endothelium tone.

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