Author Question: An area of the lung has no ventilation but is normally perfused by the pulmonary circulation. Which ... (Read 52 times)

OSWALD · **on:** Jul 16, 2018

An area of the lung has no ventilation but is normally perfused by the pulmonary circulation. Which of the following statement(s) is/are correct?

1. Blood exiting the pulmonary capillary will have a PO2 = 40 and a PCO2 = 46.
2. The area represents an alveolar shunt.
3. The is 0.
a. 2 and 3 only
b. 1 and 3 only
c. 2 only
d. 1, 2, and 3

Question 2

Regarding pulmonary blood flow in the upright lung, which of the following statements is true?

a. The apexes receive approximately 20 times more blood flow than the bases.
b. The bases receive approximately 20 times more blood flow than the apexes.
c. The greatest blood flow is found at the apexes of the lungs.
d. The pulmonary circulation is a high-pressure system.

joanwhite · **Reply #1 on:** Jul 16, 2018

Answer to Question 1

ANS: D
With no ventilation to remove carbon dioxide and restore fresh O2, the makeup of gases in these areas is like that of mixed venous blood (PO2 = 40 mm Hg; PCO2 = 46 mm Hg). The / is 0. Ve-nous blood entering areas with / ratios of 0 cannot pick up O2 or unload carbon dioxide and leave the lungs unchanged. For such areas to be distinguished from true anatomical shunts, exchange units with / values of 0 are called alveolar shunts. Although small anatomical shunts are normal, alveolar shunts are not.

Answer to Question 2

ANS: B
Farther down the lung, perfusion increases linearly in proportion to the hydrostatic pressure so the lung bases receive nearly 20 times as much blood flow as do the apexes.