Which statement about the diaphragm is true?

The diaphragm is indeed a muscle that plays a crucial role in respiration, specifically in separating the abdominal cavity from the thoracic cavity. This dome-shaped muscle is located at the base of the thoracic cavity. Its position acts as a divider, allowing for the separation of the structures and organs within the abdominal cavity from those within the thoracic cavity, which includes the lungs and heart.

When the diaphragm contracts during inhalation, it moves downward, increasing the volume of the thoracic cavity and allowing air to flow into the lungs. Conversely, when it relaxes, it moves upward, which helps expel air from the lungs during exhalation. However, the key aspect here is its anatomical role as a separator.

The other responses focus on different functions or roles of the diaphragm that don't accurately reflect its primary functions or anatomical characteristics. The diaphragm is primarily involved in inhalation rather than exhalation, and its role in gas exchange occurs indirectly via its function in ventilation rather than as a site for gas exchange. Gas exchange primarily occurs in the alveoli of the lungs, not in the diaphragm itself. Thus, the statement that accurately describes the diaphragm is its role as a separator between the abdominal and thoracic cavities.