Polarized light micrograph of lyophilized bovine hemoglobin. Blood carries oxygen in the red blood cells or erythrocytes of all vertebrates, from the lungs to the body's tissues, and returns carbon dioxide from the tissues back to the lungs permitting aerobic respiration. Each erythrocyte contains approximately 280 million hemoglobin molecules. Two of the hemoglobinopathies caused by a mutation in the hemoglobin chain are sickle-cell anemia and thalassemia. Hemoglobin deficiency causes anemia and hypoxia (insufficient oxygen supply to tissues). In other cells, like some neurons, macrophages, alveolar cells, and mesangial cells, hemoglobin has a function as an antioxidant and a regulator of iron metabolism. Field of view size: 0.740 x 1.110 mm (0.0291 x 0.0437 in)