Evolution of the spleen

Figure 21.1 Site of erythropoietic tissue in fetus and throughout life.

Figure 21.1 Site of erythropoietic tissue in fetus and throughout life.

Fetal Splenic CirculationFetal Splenic Circulation
Figure 21.2 The circulation ofthe spleen. O, open system; C, closed system (see text).

of a fibroblast-like reticular meshwork containing numerous macrophages and erythrocytes. The cords and sinuses communicate by narrow inter-endothelial spaces in the sinus wall (open system).

A few arteries enter the sinuses directly and connect via the collecting vein to the trabecular vein (closed system).

There is thus both a rapid and a slow transit component in the splenic circulation. The rapid transit is of the order of 1-2 min; the slow mixing, which occurs notably when there is splenomegaly (see later), has a circulation time of 30-60 min or even longer. In normal subjects, the blood flows through the spleen as rapidly as through other organs, at a rate of about 5% of the blood volume per minute, so that each day the blood has repeated passages through the spleen. During the flow, by a process of plasma skimming, the plasma and the leucocytes pass preferentially to the white pulp, while the red cells remain in the axial stream of the central artery. The passage of cells into the sinuses is controlled by their ability to squeeze through the interendo-thelial spaces, assisted by contraction of the reticular cells.

The red cells are normally flexible, whereas cells with abnormal membranes, or with inclusions that render them relatively inflexible, remain in the cords where they either become conditioned for later transit or are destroyed.

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  • christopher
    What is the circulation of spleen?
    3 years ago

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