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Ch. 22 The Respiratory System
All textbooksMarieb, Hoehn 7th EditionCh. 22 The Respiratory SystemProblem 6
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Chapter 21, Problem 6

When the inspiratory muscles contract, a. the size of the thoracic cavity increases in diameter, b. the size of the thoracic cavity increases in length, c. the volume of the thoracic cavity decreases, d. the size of the thoracic cavity increases in both length and diameter.

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1
Identify the primary inspiratory muscles involved in breathing, which are the diaphragm and the external intercostal muscles.
Understand that when the diaphragm contracts, it moves downward, increasing the vertical dimension (length) of the thoracic cavity.
Recognize that the contraction of the external intercostal muscles elevates the ribs, increasing the lateral and anteroposterior dimensions (diameter) of the thoracic cavity.
Combine the effects of both muscle groups to determine how the overall size of the thoracic cavity changes during inspiration.
Conclude that the contraction of the inspiratory muscles results in an increase in both the length and diameter of the thoracic cavity, leading to an increase in its overall volume.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Respiratory Mechanics

Respiratory mechanics refers to the physical principles governing the movement of air into and out of the lungs. It involves the actions of the diaphragm and intercostal muscles, which, when contracted, expand the thoracic cavity, allowing air to flow into the lungs. Understanding these mechanics is crucial for analyzing how changes in thoracic cavity dimensions affect breathing.
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Thoracic Cavity Dynamics

The thoracic cavity is the chamber within the rib cage that houses the lungs and heart. When the inspiratory muscles contract, the thoracic cavity's volume increases, leading to a decrease in internal pressure, which facilitates air inflow. Recognizing how the dimensions of the thoracic cavity change during inspiration is essential for understanding respiratory physiology.
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Inspiration Process

Inspiration is the process of taking air into the lungs, primarily driven by the contraction of the diaphragm and intercostal muscles. This contraction increases the thoracic cavity's volume, resulting in a pressure gradient that draws air in. A clear grasp of the inspiration process is vital for interpreting the effects of muscle contraction on thoracic cavity size and respiratory function.
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