Shape and Size of Red Blood Cells. Normal red blood cells, shown in Figure 32-3, are biconcave discs having a mean diameter of
about 7.8 micrometers and a thickness of 2.5 micrometers at the thickest point and 1 micrometer or
less in the center. The average volume of the red blood cell is 90 to 95 cubic micrometers. The shapes
of red blood cells can change remarkably as the cells squeeze through capillaries. Actually, the red
blood cell is a ―bag‖ that can be deformed into almost any shape. Furthermore, because the normal cell
has a great excess of cell membrane for the quantity of material inside, deformation does not stretch
the membrane greatly and, consequently, does not rupture the cell, as would be the case with many
other cells.
