Carboxyhemoglobin is a stable complex of carbon monoxide and hemoglobin (Hb) that forms in red blood cells upon contact with carbon monoxide (CO). 


Small concentrations of CO hinder the ability of Hb to deliver oxygen to the body, because carboxyhemoglobin forms more readily than does oxyhemoglobin (HbO2). 



Carbon monoxide has a 200 times greater affinity to heme proteins than oxygen.



CO is produced in normal metabolism and is also a common chemical. 



Tobacco smoking raises the blood levels of COHb by a factor of several times from its normal concentrations.



Hemoglobin contains four heme groups each capable of reversibly binding to one oxygen molecule.



Oxygen binding to any of these sites causes a conformational change in the protein, facilitating binding to each of the other sites. 



Carbon monoxide binds to hemoglobin at the same sites as oxygen, but approximately 210 times more tightly.[



Carboxyhemoglobin cannot be released as easily as oxygenThe slow release rate of carbon monoxide causes an accumulation of CO-bound hemoglobin molecules as exposure to carbon monoxide continues. 



Fewer hemoglobin particles are available to bind and deliver oxygen, thus causing the gradual suffocation associated with carbon monoxide poisoning.



Less hemoglobin available to transport oxygen from the lungs to the rest of the body resulting in death-known as carboxyhemoglobinemia or carbon monoxide poisoning.



In lesser  amounts COHb leads to oxygen deprivation of the body causing tiredness, dizziness, and unconsciousness.



COHb has a half-life in the blood of 4 to 6 hours. 



The half-life of COHB can be reduced to 70 to 35 minutes by then administration of pure oxygen.



Treatment in a hyperbaric chamber is a more effective manner of reducing the half-life of COHb.



COHb increases the risk of having thromboembolic disease.



Pregnant smokers may give birth to babies of a lower birth mass: 


fetal hemoglobin takes up carbon monoxide more readily than in an adult, therefore the fetus of a smoker will suffer from mild hypoxia, potentially retarding its development.



Carbon monoxide is produced   naturally by the action of heme oxygenase 1 and 2 on the heme from hemoglobin breakdown, producing a certain amount of carboxyhemoglobin in normal persons, even if they do not breathe carbon monoxide.







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