What is the function of the diaphragm in the respiratory system?

The correct answer is that the diaphragm separates the chest cavity from the abdominal cavity. This muscle plays a crucial role in breathing, as its contraction and relaxation influence the volume of the thoracic cavity. When the diaphragm contracts, it moves downward, increasing the chest cavity's volume and allowing the lungs to expand; this creates a negative pressure that draws air into the lungs. Conversely, when the diaphragm relaxes, it moves back up, reducing the chest cavity's volume, which helps expel air from the lungs. Thus, the diaphragm is essential not only in separating the two cavities but also in facilitating the process of inhalation and exhalation.

Other options do not accurately describe the function of the diaphragm. For instance, filtering oxygen from the atmosphere is a function of the respiratory system primarily involving the nasal passages and the lungs, while protection against infection is the role of the immune system and anatomical structures like the pleura. Assisting in the expulsion of food pertains primarily to muscular contractions within the esophagus and is not related to the diaphragm’s role in respiration.