Biconcave disc

In geometry and mathematical biology, a biconcave disc — also referred to as a discocyte[1] — is a geometric shape resembling an oblate spheroid with two concavities on the top and on the bottom.

A biconcave disc can be described mathematically by 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.