Hemoglobin, << HEE muh `gloh` buhn, >> is the pigment that transports oxygen in the blood. It is in the red blood cells and gives blood its red color. When the red cells file through the alveoli, or air sacs, of the lungs, they take up oxygen. The hemoglobin combines with the oxygen to form a compound called oxyhemoglobin. When the red cells travel through the rest of the body, they give up the oxygen to the tissues. In the tissues, the hemoglobin takes up carbon dioxide, and releases it in the alveoli of the lungs. The carbon dioxide is then exhaled.
Hemoglobin is a complex molecule that includes iron and a protein called globin. Anemia may result from a lack of hemoglobin or from hereditary abnormalities in the hemoglobin (see Anemia ). Some poisons combine with hemoglobin in a way that it can no longer combine with oxygen. Thus, aniline dyes and other chemicals cause the formation of methemoglobin, which cannot take up oxygen. The blood then turns bluish-brown. Carbon monoxide, a poisonous gas, mixes readily with hemoglobin, making the blood bright-red. But the gas keeps blood from taking up oxygen.
Scientists have identified many different kinds of hemoglobin. A person’s hemoglobin type is inherited. Hemoglobin A ranks as the most common type. One abnormal type, called hemoglobin S or sickle hemoglobin, causes the disease sickle cell anemia. Red blood cells that contain mostly hemoglobin S may become stiff and misshapen. These cells may then plug blood vessels. See Sickle cell anemia .
