Biconcave disc

A biconcave disc can be described mathematically by

${\displaystyle z(r)=D{\sqrt {1-{\frac {4r^{2}}{D^{2}}}}}\left(a_{0}+{\frac {a_{1}r^{2}}{D^{2}}}+{\frac {a_{2}r^{4}}{D^{4}}}\right)}$

where z(r) is the height of the surface as a function of radius r, D is the diameter of the disc, and a₀, a₁, a₂ are coefficients describing the shape. The above model describes a smooth surface; actual cells can be much more irregular.

Erythrocytes are in the shape of a biconcave disc. An erythrocyte is also known as a red blood cell and transports oxygen to and from tissues. [1][3]