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The diaphragm is the most important muscle of respiration, [3] and separates the thoracic cavity, containing the heart and lungs, from the abdominal cavity: as the diaphragm contracts, the volume of the thoracic cavity increases, creating a negative pressure there, which draws air into the lungs. [4]
This compresses the abdominal cavity, raises the ribs upward and outward and thus expands the thoracic cavity. This expansion draws air into the lungs. When the diaphragm relaxes, elastic recoil of the lungs causes the thoracic cavity to contract, forcing air out of the lungs, and returning to its dome-shape. [1]
The lungs which are located in the thoracic cavity, are protected from physical damage by the rib cage. At the base of the lungs is a sheet of skeletal muscle called the diaphragm. The diaphragm separates the lungs from the stomach and intestines.
The lungs are not capable of inflating themselves, and will expand only when there is an increase in the volume of the thoracic cavity. [6] [7] In humans, as in the other mammals, this is achieved primarily through the contraction of the diaphragm, but also by the contraction of the intercostal muscles which pull the rib cage upwards and outwards as shown in the diagrams on the right. [8]
structures of the respiratory system, including the diaphragm, trachea, bronchi and lungs [1] structures of the digestive system, including the esophagus, endocrine glands, including the thymus gland, structures of the nervous system including the paired vagus nerves, and the paired sympathetic chains, lymphatics including the thoracic duct.
"Hiccups are recurrent, uncontrollable contractions or spasms of the diaphragm that cause the larynx and vocal cords to close suddenly, which forces air into the lungs and creates the 'hic' sound ...
The lungs expand and contract during the breathing cycle, drawing air in and out of the lungs. The volume of air moved in or out of the lungs under normal resting circumstances (the resting tidal volume of about 500 ml), and volumes moved during maximally forced inhalation and maximally forced exhalation are measured in humans by spirometry. [12]
Air enters the lungs as the diaphragm strongly contracts, but unlike during traditional relaxed breathing the intercostal muscles of the chest do minimal work in this process. The belly also expands during this type of breathing to make room for the contraction of the diaphragm. [3]