Red Blood Cell Picture; this image is 500 pixels across the
is 4096 x 4096 pixels.
Erythrocytes are discoid cells that lack a nucleus and are filled with haemoglobin (hemoglobin) an iron containing pigment that binds with oxygen and carbon dioxide. The red colour of haemoglobin is what makes blood red. Haemoglobin binds very powerfully to carbon monoxide. Carbon monoxide therefore displaces oxygen and accounts for the danger of this gas. The circulation of the blood, powered by the heart, is what delivers oxygen (bound to haemoglobin in the red blood cells) to all parts of the body. Red blood cells are deformable, allowing them to squeeze through capillaries, the tiny blood vessels where gas exchange with the tissues occurs. A lower than normal concentration of RBCs is called anaemia (anemia) and has many causes.