MCAT Biology Question 89: Answer and Explanation

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Question: 89

14. In emphysema, the alveolar walls are destroyed, decreasing the recoil of the lung tissue. Which of the following changes may be seen in a patient with emphysema?

  • A. Increased residual volume
  • B. Decreased total lung capacity
  • C. Increased blood concentration of oxygen
  • D. Decreased blood concentration of carbon dioxide

Correct Answer: A

Explanation:

The intrinsic elastic properties of the lung are important during exhalation as the passive recoil of lung tissue helps decrease lung volume. With decreased recoil, the patient will have difficulty exhaling completely, increasing the residual volume. The total lung capacity would be expected to increase in this case because there would be less recoil opposing inhalation, eliminating choice (B). With decreased alveolar surface area, one would expect decreased gas exchange, which would decrease blood concentrations of oxygen while increasing blood concentrations of carbon dioxide, eliminating choices (C) and (D).

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