red blood cell

The structure of a human red blood cell. Their concave surfaces give them a large surface area for the transportation of haemoglobin.

Most common type of blood cell, and responsible for transporting oxygen around the body. They contain haemoglobin, a red protein, which combines with oxygen from the lungs to form oxyhaemoglobin. When transported to the tissues the oxyhaemoglobin splits into its original constituents, and the cells are able to release the oxygen. There are about 6 million red cells in every cubic centimetre of blood.

The red cell is a highly specialized cell with a distinctive shape. In mammals they are in the shape of a disc with a depression in the face of the disc and lose their nucleus before they work as oxygen transporters in order to make maximum space for haemoglobin. In other vertebrates they are oval and nucleated. They are manufactured in the bone marrow. In humans, red cells last for only four months before being destroyed in the liver. Haemoglobin contains iron, which is why this mineral must be included as part of a balanced diet. However, the liver can store and re-use iron from old red cells.