Which of the following are effects of surface tension forces in ...

[2125004343]

Which of the following are effects of surface tension forces in the air-filled lung?
 
  1. It increases the elastic recoil of the lung (promoting collapse).
  2. It makes the lung harder to inflate than if it were filled with fluid.
  3. It decreases the lung's elasticity as volume increases.
  a. 1 and 2 only
  b. 2 and 3 only
  c. 1 and 3 only
  d. 1, 2, and 3

Question 2

During normal tidal ventilation, the transpulmonary pressure gradient (Palv  Ppl) reaches its maximum value at what point in the cycle?
 
  a. Midinspiration
  b. End-expiration
  c. End-inspiration
  d. Mid-expiration

[cuttiesgirl16]

Answer to Question 1

ANS: A
Less pressure is needed to inflate a fluid-filled lung to a given volume. This phenomenon indi-cates that a gas-fluid interface in the air-filled lung changes its inflation-deflation characteristics. The recoil of the lung is therefore a combination of tissue elasticity and these surface tension forces in the alveoli. During inflation, additional pressure is needed to overcome surface tension forces.

Answer to Question 2

ANS: C
At this point, called end-inspiration, alveolar pressure has returned to 0 and the transpulmonary pressure gradient reaches its maximal value (for a normal breath) of approximately 10 cm H2O.

[2125004343]

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