Anatomy and Physiology II Practice Test

The primary function of the diaphragm during respiration is centered around its role in the mechanics of breathing. When the diaphragm contracts, it moves downward, which increases the volume of the thoracic cavity. This increase in volume creates a negative pressure in the thoracic cavity relative to the atmospheric pressure, allowing air to flow into the lungs; this process is known as inhalation. During exhalation, the diaphragm relaxes and moves upward, which decreases the volume of the thoracic cavity and helps push air out of the lungs. This action of the diaphragm is crucial for efficient breathing, making it the main muscle involved in this process.

Other options, while related to functions of other systems or processes, do not pertain to the diaphragm's primary role in respiration. Filtering air is primarily the function of the nasal passages and respiratory mucosa. Producing vocal sounds involves other structures like the vocal cords in the larynx. Assisting in swallowing is mainly the function of the esophagus and associated muscles rather than the diaphragm itself. Thus, the correct answer emphasizes the diaphragm's essential role in changing the volume of the thoracic cavity to facilitate breathing.