Chapter 4, Problem 7RQ

### Cardiopulmonary Anatomy & Physiolo...

7th Edition
Des Jardins + 1 other
ISBN: 9781337794909

Chapter
Section

### Cardiopulmonary Anatomy & Physiolo...

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

# The normal transit time for blood through the alveolar-capillary system is aboutA. 0.25 secondB. 0.50 secondC. 0.75 secondD. 1.0 second

Summary Introduction

Introduction:

The major function of the respiratory system is the exchange of gases. This exchange of gases takes place between alveolar space and capillaries. The oxygen inspired is exchanged with carbon dioxide being carried by the deoxygenated blood. This exchange takes place when carbon dioxide from the capillaries moves to alveolar spaces and oxygen moves from the alveolar space to capillaries. This exchange keeps taking place until an equilibrium is attained.

Explanation

Justification/ Explanation for the correct answer:

Option (C) is 0.75 seconds. The transit time in resting position, signifying the normal condition for blood to move through the alveolar capillary system is 0.75 seconds. When blood enters the system, the gaseous exchange between oxygen and carbon dioxide takes place. This exchange takes place in one-third of the transit time available. The oxygen pressure gradient within this system is 60 mm Hg and that of carbon dioxide is 6 mm Hg. This difference allows a faster diffusion and exchange of the gases. Hence, option (B) is correct.

Option (A) is 0.25 seconds. This is not the transit time for blood in the alveolar-capillary system, in resting conditions...

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