The human red blood cell
There are more red blood cells (erythrocytes) in our bodies
than any other sort of cell. In fact, there are an amazing
25 trillion (*) (that is 25000000000000) on average in an adult!
They are very simple cells, little more than bags containing
the hemoglobin (*) molecules so essential to our lives. It is the
hemoglobin molecules that carry oxygen from the lungs to the
rest of the body. Red blood cells actually loose many components
of a normal cell (such as a nucleus) during development and are
doomed to short life of about 120 days. Thus we must produce
200 billion (*) new red blood cells every day.
Photograph by J Houseman.
From BIODIDAC archive.
Red blood cells must travel to every corner of the body and the
smallest blood vessels, the capillaries, are so narrow that
single red blood cells have to bend and fold to fit through.
Only fairly recently, studies of the cell membrane and internal
structures have shown how these cells can undergo such deformations
and then spring back to their normal shape.