BIOLOGY Volume 2 - A Guide to General Biology - 2004

14. TRANSPORT IN ANIMALS

14.8. Functions of blood in mammals

14.8.3. Carbon monoxide and hemoglobin

The affinity of iron(II) in Hemoglobin for carbon monoxide (CO) is approximately 250 times greater than for oxygen. Therefore, even in the presence of very small amounts of CO, hemoglobin preferentially binds to it, forming a highly stable compound called carboxyhemoglobin. Under these conditions, oxygen can no longer bind to hemoglobin, and its transport by the Blood ceases. In an atmosphere with a high concentration of carbon monoxide, a person quickly loses consciousness, and unless the victim is exposed to fresh air in time, death from asphyxia is inevitable. A CO concentration of just 0.1% (a partial pressure of approximately 0.6 mm Hg) can be fatal. Carboxyhemoglobin has a cherry-red color, which often imparts a characteristic hue to the Skin of Carbon monoxide poisoning victims. The patient must be provided with breathing air consisting of nearly pure oxygen with a small admixture of carbon dioxide. The latter stimulates the respiratory center in the Medulla Oblongata, causing accelerated breathing, which helps eliminate carbon monoxide from the Lungs. Nearly pure oxygen is administered because its partial pressure in normal air is insufficient to displace carbon monoxide from carboxyhemoglobin, i.e., to restore the supply of physiologically active hemoglobin in the blood.

Two widespread environmental sources of carbon monoxide are automobile exhaust fumes and tobacco smoke.