Library · Physiology
Mechanics of breathing
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The diaphragm is the sheet of muscle that separates the chest from the abdomen, and it is the most important muscle of inspiration, that is, of drawing air in.
When it contracts, the diaphragm pulls down on its central tendon, the firm part at its center, and increases the height of the chest. The chest cavity enlarges, the pressure inside drops below the pressure outside, and air flows in because of that difference. Nothing pushes it: it comes in on its own.
The muscles of the chest wall help by moving the ribs, and with that movement they also change the volume of the cavity.
Think of a bellows: when it opens, air flows in on its own. When the effort stops, air flows out and what stays in the lungs is the functional residual capacity, the volume that remains after a passive exhalation.
In brief
The diaphragm is the most important muscle of inspiration: when it contracts, it enlarges the chest cavity and lowers the pressure inside the thorax.
It pulls down on its central tendon, increases the vertical diameter of the chest, and that negative pressure draws air in.
A bellows: when it opens, air flows in on its own.
The chest wall muscles help by moving the ribs, which changes the volume of the cavity.
What remains in the lungs after a passive exhalation is the functional residual capacity.
Sources (3)
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Thorax: Diaphragm, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingAnatomy, Thorax, StatPearlsPublished
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Pulmonary Compliance, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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