How does the diaphragm change the size of the chest cavity during inhalation?

The diaphragm is a dome-shaped muscle that serves as the primary driver of respiration. During inhalation, the diaphragm contracts, which increases the internal height of the thoracic cavity.1

This expansion of the chest cavity lowers the internal pressure within the lungs, creating a pressure gradient that draws air into the respiratory system through a process known as inspiration. While the lungs naturally tend to collapse due to their elastic recoil, the contraction of the diaphragm and the chest wall effectively overcomes this inward pull, allowing the lungs to inflate. When the diaphragm subsequently relaxes, the natural elasticity of the lung tissue and the thoracic cage causes the chest cavity to return to its resting state, facilitating expiration.12