Definition of Hemoglobin

HemoglobinHemoglobin is a combined protein within erythrocytes (red blood cells) that is crucial to the oxygen-carbon dioxide exchange.

Two proteins come together to form hemoglobin: heme, a reddish pigment that contains iron, and globin.

Hemoglobin bonds loosely with oxygen and carbon dioxide molecules, depending on which is in higher concentration.

In the lungs, oxygen molecules have the higher concentration and bind with the hemoglobin. As the blood carries the erythrocytes deeper into the body where oxygen concentrations are lower, the bond becomes less stable.

When the erythrocytes reach the capillary beds where the concentration of carbon dioxide is higher than the concentration of oxygen, the hemoglobin releases its oxygen molecules and replaces them with carbon dioxide molecules and carries the carbon dioxide back to the lungs where the exchange repeats.

Cigarette Smoking and Carbon Monoxide Level

Cigarette smoke contains high levels of carbon monoxide. Heavy smokers may have blood concentrations of carbon monoxide of 7 to 9 percent.

Carbon monoxide binds more strongly with hemoglobin than oxygen or carbon dioxide, forming a tight bond (the compound carboxyhemoglobin) that blocks hemoglobin from binding with either. Only small amounts of carbon monoxide inhaled into the lungs can interfere with the oxygen-carbon dioxide exchange significantly enough to cause poisoning (hypoxia) or death.

Carbon monoxide begins to cause symptoms of oxygen deprivation when its blood concentration reaches 10 percent, impairs neurologic function at 30 percent, and can cause death at 50 percent. A gas commonly present in the environment, carbon monoxide is a byproduct of incomplete combustion.

See also ANEMIA; HEMOCHROMATOSIS; INHALED TOXINS; SICKLE CELL DISEASE; SMOKING AND HEALTH; THALASSEMIA.

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