Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
ISBN: 9781337794909



Cardiopulmonary Anatomy & Physiolo...

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

At birth, the number of alveoli represents; about how much of the total adult gas exchange units?

A. 10 percent

B. 20 percent

C. 30 percent

D. 40 percent

Summary Introduction


The respiratory system is one of the vital biological systems, of which the lungs are the most important component. The alveoli present within the lungs are the basic unit of ventilation. They form the end part of the respiratory system and are the site of gas exchange with the blood. These are exclusively found as a part of the mammalian lungs. The alveoli are formed in the fetus during the alveolar stage of lung development.


Explanation for the correct answer:

Option (a) is,‘10 percent.’ The alveolar period begins by about 32 weeks of gestation and continues throughout the childhood for up to 8 to 12 years. The alveoli continue to grow and proliferate during this period. The number of alveolar capillary units increases to nearly 300 million at the end of the alveolar phase. There are about 2 million primitive alveoli at the time of birth and this accounts for 10% of the adult gas exchange units. Hence, option (a) is the correct answer.

Explanation for the incorrect answer:

Option (b) is, ‘20 percent.’ The number of alveoli is around 24 million at birth and this represents 10% of the adult gas exchange units...

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