What is the diaphragm function?

   The diaphragm is the sheet of muscle and connective tissue that separates the chest cavity and the abdominal cavity. The diaphragm extends from the sternum, or breastbone, along the lower ribs, and downward to the lumbar vertebrae. The descending aorta, the esophagus, and the inferior vena cava pass through the diaphragm. The diaphragm contracts and relaxes during respiration. When relaxed, the diaphragm is dome-shaped. During inhalation its muscles contract, pulling it downward. At the same time the muscles of the chest contract, pulling the ribs upward and outward. This combined muscle action increases the volume of the chest cavity, decreasing the pressure within it. As a result, air passes into the lungs, expanding them to fill the chest cavity. When the diaphragm relaxes, it again moves upward. This, combined with the relaxation of the chest wall muscles, causes air to pass out of the lungs.