The curved structure that separates the chest cavity from the abdominal cavity is called the diaphragm. This muscular wall plays a vital role in respiration. When the diaphragm contracts, it moves downward, enlarging the chest cavity and decreasing the pressure inside, allowing air to flow into the lungs. Conversely, when it relaxes, the diaphragm moves upward, pushing air out of the lungs. The diaphragm is essential not only for breathing but also for supporting the organs in the abdominal cavity.