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O, and CO_. Exchangr

RESPIRATORY PHYSIOLOGY

Figurę 5.19 0₂ and CO, Exchange

As blood flows Ihrough thp alveolar capillary, Oj diffuses from ihe alvcolus into Ihe red blood celi. where ii binds io hemoglobin. Al ihe same limę, CO? diffuses out of ihe red blood celi and inlo the alveo-lus. Normally, blood lraverses ihe entire length ot the capillary in 0.75 second. With increased cardiac output, the transit time is reduced. Fuli equilibration of blood with alveolar O., and CO^ still occurs with transit timcs as Iow as 0.5 second. In some disease st.r-there is thickening of the alveolar<apillary wali. This reslricts the dr fusion of O. and CO. and can preveni fuli equilibration of blood w the ahreolar gases during the time recjuirod for the blood to travel lengtli oi the capillary (dashed lines labeled as abnormal).

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