Hemoglobin is a protein-based component of red blood cells which is primarily responsible for transferring oxygen from the lungs to the rest of the body. Hemoglobin is actually the reason red blood cells appear red, although oxygen-rich blood is noticeably brighter than the depleted blood returning to the heart and lungs. Fresh hemoglobin is produced in the bone marrow as needed.

The creation of hemoglobin is controlled by a complicated genetic code. Because unborn babies obtain their oxygenated blood from their mothers and not their own lungs, two separate substances called hemoglobin alpha and hemoglobin gamma combine with several nitrogen atoms and one iron atom. This allows the fetus to receive oxygen-rich blood without respiration. Once the infant is born, however, the body replaces hemoglobin gamma with a new variant called hemoglobin beta. The combination of these two substances continues for a lifetime.

Essentially, hemoglobin develops a hunger for oxygen molecules. When the blood is carried into the lungs, hemoglobin proteins containing iron atoms attract whatever oxygen is available. This oxygenated blood then travels throughout the entire bloodstream, releasing oxygen into the muscles and organs. The spent red blood cells are transferred to the gastrointestinal system for disposal and new red blood cells with hemoglobin take their place in the bloodstream.

This ongoing system of hemoglobin proteins obtaining oxygen from the lungs and delivering it to the cells is based on ideal conditions, however. Sometimes the alpha or beta proteins produced by the genetic code are not perfectly formed, as in the case of sickle cell anemia. One of the components is shaped like a sickle, causing an imperfect bond to form.

Anemia means that the red blood cells lack sufficient levels of iron. Without an iron atom, the damaged hemoglobin pigment cannot attract oxygen in the lungs very effectively, if at all. The result can be a slow wasting process leading to complete body dysfunction.

Hemoglobin can also be compromised by blood conditions such as diabetes or cancer. Many standard blood tests included a general check of hemoglobin levels. The amount of glucose in the bloodstream may vary from hour to hour, but an examination of hemoglobin often provides a more accurate reading for diabetics.

Another difficulty with hemoglobin is its affinity for gases other than oxygen. Hemoglobin is 200 times more attracted to carbon monoxide than oxygen, for example. This means that someone breathing in carbon monoxide from automobile exhaust could be replacing the oxygen in their lungs with a poison. If enough hemoglobin is exposed to carbon monoxide, the result could be the same as asphyxiation. Cigarette smokers who regularly breath in carbon monoxide could compromise as much as 20% of their total lung oxygen supply.

This attraction to other gases can actually be beneficial under controlled circumstances. Hemoglobin is also attracted to gases used during anesthesia proceedings before surgery. The nitrous oxide or other breathable anesthetic is carried into the brain through the hemoglobin, which allows the surgical team to control the patient's level of consciousness. As oxygen is reintroduced into the patient's lungs, the hemoglobin refreshes itself and the other gases become waste products.