What is the main role of the diaphragm in respiration?

The primary role of the diaphragm in respiration centers around its function as a muscle that facilitates breathing. When the diaphragm contracts, it moves downwards, effectively increasing the volume of the thoracic cavity. This increase in volume leads to a decrease in pressure within the thoracic cavity relative to atmospheric pressure, allowing air to flow into the lungs. This process is vital for inhalation; without the diaphragm's contraction to expand the cavity, sufficient air would not be drawn into the lungs.

While other options mention various respiratory functions, they do not accurately describe the diaphragm's main role. Filtering air pertains more to the nasal passages and mucous membranes, pushing air out involves abdominal muscles and lung elasticity rather than the diaphragm's primary action, and supporting the upper respiratory tract structures relates to different anatomical components, not directly to the diaphragm's function in breathing mechanics.