The diaphragm is a fibromuscular or musculotendinous structure that separates the thoracic cavity from the abdominal cavity.
It is pierced by the structures that will pass between the chest and the abdomen.
It is developed from an inner transverse layer of body wall muscles.
Function:
The diaphragm helps in the inspiration and expiration of air in and out of the lungs.
At the time of inspiration, the diaphragm contracts, increasing the pulmonary volume, thereby reducing the intrapulmonary pressure to less than the atmospheric pressure, and air moves into the lungs.
At the time of expiration, the diaphragm relaxes, reducing the pulmonary volume and thereby increasing the intrapulmonary pressure slightly more than the atmospheric pressure.
This leads to the expulsion of air from the lungs.