What is the primary function of the diaphragm in respiration?

The primary function of the diaphragm in respiration is to contract and relax, which leads to changes in lung volume. When the diaphragm contracts, it moves downward, increasing the thoracic cavity's volume. This expansion lowers the pressure in the lungs below atmospheric pressure, causing air to flow in (inhalation). Conversely, when the diaphragm relaxes, it moves back upward, decreasing the thoracic cavity's volume and increasing lung pressure, which facilitates air expulsion (exhalation). This fundamental mechanism of altering lung volume is crucial for effective breathing and is central to the process of ventilation in the respiratory system.

The other choices involve functions associated with respiration but do not accurately describe the primary role of the diaphragm. While regulating airflow and controlling breathing rate are important aspects of respiratory physiology, they are not directly performed by the diaphragm itself. Gas exchange, which occurs in the alveoli of the lungs, is independent of diaphragm function and relates more to the diffusion of gases rather than the mechanical processes of ventilation driven by diaphragmatic movement.