In capillaries white blood cells tend to flow with a lower velocity than red blood cells. This is
due to the larger volume of the white cells and their spherical shape as compared to that of
the red cells with their biconcave disk shape, as well as to the smaller deformation of the
white cell during flow in narrow blood vessels. As a result, red blood cells often accumulate
upstream of a white cell in a capillary with a single file of cells, whereas downstream of the
white cell a red cell depleted region is formed. When the white cell enters a postcapillary …