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, resulting in the net diffusion of carbon dioxide into the capillaries. However, themetabolic activity of many tissues is quite variable, which is reflected in a variable tissue venous PO2and PCO2, which means that, once blood reaches the right ventricle, it is referred to as mixed venous blood, with a PO2of 40 mm Hg and a PCO2of 46 mm Hg. When physical activity increases, PO2decreases as PCO2increases. The partial pressures of alveolar gases are determined by the partial pressures of gases in the inspired air (determined primarily by altitude),minute ventilation, and the rate of tissue metabolic activity. Thus, the crucial factor in determining alveolar partial pressure is the alveolar ventilation relative to metabolic activity (oxygen consumption and carbon dioxide production). When alveolar ventilation increases relative to metabolic activity, alveolar PO2increases and PCO2decreases. In contrast, an increase in metabolic activity relative to alveolar ventilation will decrease PO2and increase PCO2.Diff: 5 Page Ref: 48126
3) The solubility of oxygen in solution is relatively low, necessitating the presence of hemoglobin to carry oxygen to active tissues. Hemoglobin exhibits several unique characteristicsthat make it well suited for the transport of oxygen. Describe the structure of hemoglobin and themechanisms that can alter the affinity of hemoglobin for oxygen.