Hemoglobin is a red protein found in the red blood cells of vertebrates that carries oxygen from the lungs to body tissues. Hemoglobin also carries carbon dioxide from body tissues back to the lungs.
One hemoglobin molecule in a mammal can carry up to four oxygen molecules. Hemoglobin also carries nitric oxide, an important regulatory molecule, and releases nitric oxide when it releases oxygen. Hemoglobin saturated with oxygen is called oxyhemoglobin, and hemoglobin without any oxygen is known as deoxyhemoglobin. Oxyhemoglobin is formed during physiological respiration when oxygen binds to the heme component of hemoglobin. This occurs in the pulmonary capillaries of the lungs.
The oxygen then travels through the blood stream to cells where it is used as a terminal electron acceptor in the process of oxidative phosphorylation to produce adenosine triphosphate, or ATP. Hemoglobin contains about 70 percent of the iron found in mammals. Iron is vital to blood production and proper immune function.
Blood loss is the most common cause of iron deficiency. Donating blood results in the loss of 200 to 250 milligrams of iron.The iron level of the donor is checked before each donation to ensure it is safe for the donor to give blood.