The structure that separates the chest cavity from the abdominal cavity is the diaphragm. The diaphragm is a dome-shaped muscle that plays a crucial role in the respiratory process. When you inhale, the diaphragm contracts and moves downward, creating a vacuum that allows air to flow into the lungs. Conversely, when you exhale, the diaphragm relaxes and moves back to its original position, pushing air out of the lungs. In addition to facilitating breathing, the diaphragm also acts as a physical barrier between the thoracic cavity, which contains the heart and lungs, and the abdominal cavity, which houses organs such as the stomach and intestines.