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.

Blood: composition and functions. We know it contains red blood cells but what else is blood made of. Also, what is it for? What functions does it perform?