[Campbell Biology P.996] According to Figure 42.29 and the text, which of the following stat... | Practice Question

According to Figure 42.29 and the text, which of the following statements about partial pressures of O2 PO2 and CO2 PCO2 is correct?

  • A: The PO2 in exhaled air (6) is higher than the PO2 in inhaled air (1), indicating O2 uptake.
  • B: Blood returning to the heart from systemic tissues (represented by 4 before entering 5) has a lower PO2 and higher PCO2 compared to blood leaving the lungs (3).
  • C: The partial pressure of O2 in alveolar spaces (2) is lower than in the blood entering the alveolar capillaries (5), facilitating O2 diffusion into the blood.
  • D: After gas exchange in the lungs, the blood in the pulmonary veins (3) has a PO2 equal to that of inhaled air (1).

Explanation

Blood returning from systemic tissues deoxygenated blood has a low PO2 less than 40 mm Hg at point 4, 40 mm Hg at point 5 and high PCO2 greater than 45 mm Hg at point 4, 45 mm Hg at point 5 . In contrast, blood leaving the lungs oxygenated blood at point 3 has a high PO2 104 mm Hg and lower PCO2 40 mm Hg . This comparison accurately reflects the gas exchange process in the body and lungs.