How does a mammal’s diaphragm help it breathe?

The diaphragm is a dome-shaped, muscular structure that serves as the primary muscle of respiration in mammals, separating the thoracic and abdominal cavities.1

It facilitates breathing through an aspiration (suction) pump mechanism:

• Inspiration: When the diaphragm contracts, it moves downward, which increases the internal height and volume of the thoracic cavity. This expansion lowers the internal pressure within the lungs relative to the atmosphere, causing air to flow inward.12
• Expiration: Breathing out occurs primarily through the relaxation of the diaphragm. As the muscle relaxes, the natural elasticity of the lung tissue and the chest wall generates the force necessary to expel air from the lungs.12

Beyond its role in quiet breathing, the diaphragm is also essential for expulsive actions such as coughing, sneezing, and vomiting. During periods of intense physical activity, the diaphragm works in conjunction with other muscles, such as the intercostal muscles, to support increased respiratory demands.12