“Red Cell in the Blood Stream” shows a single red cell floating down the river of plasma.  The deformability and biconcave shape of the red cell is essential to its function. The red cell is about  7.5 to 8.5μm in diameter and 1.5 to 2.0 μm in thickness. They lack a nucleus. There are about 20–30 trillion red cells in the body representing 25% of cells in the body.  In contrast there are 7.4 billion people in the world

Hemoglobin is the functional marvel in the red cell.  The hemoglobin in the red cells take up oxygen in the lungs and transport it to the cells via the capillaries.  The approximately 8μm cells have to  fit into the approximately 5μm capillary.  The red cells deform and release oxygen into the tissues .