Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
ISBN: 9781337794909



Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
ISBN: 9781337794909
Textbook Problem

In the healthy lung, when the alveolus

decreases in size during a normal exhalation, the

1. surface tension decreases.

2. surfactant to alveolar surface area increases.

3. surface tension increases.

4. surfactant to alveolar surface area decreases.

A. 1 only

B. 3 only

C. 4 only

D. 1 and 2 only

Summary Introduction


The alveolar type II cells produce and store pulmonary surfactants. These are composed of proteins and phospholipids. The most important surface tension-lowering chemical is DPPC (dipalmitoyl phosphatidylcholine). It is amphipathic in nature, that is, it has a hydrophilic as well as a hydrophobic end. The hydrophilic end is toward the liquid phase and the hydrophobic end is toward the gaseous phase.


Justification for the correct answer:

Option (d) states that the surface tension reduces and the surfactant to alveolar surface area increases during normal exhalation. The alveolar size decreases during exhalation and the DPPC molecule toward the gas–liquid interface causes a decrease in the proportion to its ratio to surface area by surface tension. This means that the ratio of the surfactant to the alveolar surface increases. This also decreases the alveolar surface tension. Hence, option (d) is correct.

Justification for the incorrect answers:

Option (a) states that only the surface tension decreases during normal exhalation...

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