Page 14, Turbulence & Rheology, Dr. D. Penney

Capillary Flow (continued..)

Blood viscosity increases in capillaries, unlike the decrease due to the Fahraeus-Lindqvist effect observed in arterioles. Erythrocytes are unable to pass through tubes having a diameter less than 2.7 um. The limit of deformation of red blood cells is reached at this value since the plasma membrane does not stretch, thus there are no capillaries smaller than 2.7 um. Pushing an erythrocyte through a smaller opening causes it to rupture. Myocardial capillaries, among the smallest, are approximately 4 um in diameter.

The sieve-like network of the spleen has openings of approximately 2.7 um, a mechanism of eliminating "old" erythrocytes. Healthy red cells can pass through these openings, but the old cells or cells with defective membranes rupture. This is the major mechanism for removing erythrocytes from the circulation.

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