文档介绍：. Gas transport
Oxygen is transported by the blood in both physically dissolved and hemoglobin-bond forms.
Carbon monoxide binds the same site on hemoglobin as oxygen does and is dangerous to life.
Carbon dioxide (CO2) is transported in three forms: physically dissolved, bicarbonate, and carbaminohemoglobin
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Oxygen Transport in the Blood
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Hemoglobin (Hb)
Each Hb molecule consists of four globular protein (globin, 珠蛋白) subunits.
Each subunit posed of a protein chain tightly associated with a non-protein heme(血红素) group.
Oxygen binds to iron (Fe2+) on heme.
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Two Forms of Oxygen Exist in the Blood
Physically dissolved: 2%
Dissolved O2 (ml/dL) = (ml/dL/mmHg) X Pa O2 (mmHg)
Combined with Hb: 98%
Both physically dissolved and chemically bond are important.
Oxyhemoglobin (HbO2): Hemoglobin binds to oxygen.
Deoxyhemoglobin (Hb): Hemoglobin that does not bind with oxygen.
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Oxygen Binds to Hemoglobin
The binding of oxygen to hemoglobin is reversible and very quick.
The reaction of this biding is oxygenation but not oxidation (ferrous remains as ferrous).
Each hemoglobin molecule can bind four oxygen molecules.
Each gram of hemoglobin can bind up ~ ml of O2 (depending on methemoglobin levels).
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Positive Cooperativity
Changes in the affinity of hemoglobin as each essive O2 molecule binds to a heme site.
Binding of the first O2 molecule increases the affinity for the second O2 molecule, and so forth.
The affinity for the forth O2 molecule is the highest.
This change in affinity facilitates the loading of O2 in the lungs and the unloading of the O2 at the tissues.
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Quantitative Description of O2 Binding to Hb
Oxygen capacity is the maximum of oxygen that hemoglobin can carry per 100 ml blood .
Hb-bound oxygen content is the amount of oxygen actually carried by hemoglobin per100 ml blood.
Oxygen saturation (SO2) is the percentage saturation of hemoglobin with oxygen th