Diaphragm (anatomy)
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In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. Its Latin name is the"transversus thoracis". It separates the thoracic cavity (with lung and heart) from the abdominal cavity (with liver, stomach, intestines, etc.). In relaxed state, the diaphragm is shaped like a dome. It is critically important in respiration: in order to draw air into the lungs, the diaphragm contracts, thus enlarging the thoracic cavity and reducing intra-thoracic pressure. (The muscles between the ribs also participate in this enlargement.) When the diaphragm relaxes, air is exhaled by elastic recoil of the lung and the tissues lining the thoracic cavity.
The diaphragm also helps to expel vomit, feces, and urine from the body by increasing intra-abdominal pressure. A hiccup occurs when the diaphragm contracts periodically without voluntary control. A hiatal hernia is a tear in the diaphragm.
If the diaphragm is struck, or for other reasons, it may spasm briefly, making breathing difficult. This is called "being winded" or "having the wind knocked out of you". In some martial arts, practitioners are trained to do this.
There are three main apertures (or holes) in the diaphragm, one each for the inferior vena cava (the Foramen Venae Cavae), aorta (the Hiatus Aorticus) and oesophagus.