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OJCO, Exchange

RESPIRATORY PHYSIOLOGY

Oxygen Transport

Alveoli Red blood oflung    celi

Plasma

8ody

tissues

Oxyhemoglobin Dissociation Curve

(al pH 7.4, Pco₂ 40 mm l ig, 37° C)

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Effects of PcOj, pH, and Temperaturę on O2 Dissociation Curve

C0₂ Fquilibrium Curves

(for normal arlerial and venous blood)

Pro-j imm Hgl

Carbon Dioxide Transport

Body J- Perkin-

tissues ^MS-^MrA

^cmy

Alveoli of lung

Figurę 5.21    0₂/C0> Exchange_

During each breath, O, and CO, are exchanged across the alvcolar-pulmonary capillary membranę <see Figurę 5.19). Almost all of ihe O., carried lo ihe tissues is bound to hemoglobin (Hb); only a smali amount is dissolved and iransported in plasma. As shown in the oxy-hemoglobin dissociation curve, the binding of O., to Hb is dependent on the parlial pressure of O, (Po₂). The pcrccnt saturation of Hb (So,) is about 97.5% when the Po_? is 100 mm Hg. In the three middle panels, the effects of CO,, pH, and temperaturę on Ihe oxyhemoglo-bin dissociation curve are shown. Hb binding of O., is decreased, and ihereby off-loading of O, to the tissues is inereased by inerease-: Pco., ihypercapnia), decreased pH (acidosisi, or inereased body tern perature (fever). CO, from the tissues is transported largely in the form of HCO,-. A smali amount is transported in the dissolved form and somc is carried in the form of carbaminohemoglobin. The bot-tom leń panel shows thal Ihe CO, eąuilibrium (dissociation) curve i-much steeper than that for O,, which is włty ihe Pco, difference between arterial and mixed venous blood is smali (about 5 mm Hg¹

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