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The membrane of the red blood cell RBC is easily deformed by shearing forces while maintaining its local area nearly unchanged. This type of response is due to the structure of the membrane which is composed of a lipid bilayer supported by a scaffolding of cytoskeletal proteins. Normal human RBCs in quiescent plasma assume a biconcave discoid shape with an average diameter of 8 m, thickness of 2 m, surface area of 140 m2, and volume of 90 m3. 1 Equilibrium of forces determines the quiescent shape and it has been shown that changing the properties of the membrane leads to different quiescent shapes. 2 The surface area to volume ratio of the normal cell is 40% greater than that of a sphere with the same volume. Excess surface area not only improves the RBCs efficiency in loading and unloading solutes, but also allows the cell to deform easily as it passes through the circulatory system where it may …