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The thoracic diaphragm, or simply the diaphragm (/ ˈ d aɪ ə f r æ m /; [1] Ancient Greek: διάφραγμα, romanized: diáphragma, lit. 'partition'), is a sheet of internal skeletal muscle [ 2 ] in humans and other mammals that extends across the bottom of the thoracic cavity .
The crus of diaphragm (pl.: crura), refers to one of two tendinous structures that extends below the diaphragm to the vertebral column. There is a right crus and a left crus, which together form a tether for muscular contraction. They take their name from their leg-shaped appearance – crus meaning leg in Latin.
The mean number of alveoli in a human lung is 480 million. [11] When the diaphragm contracts, a negative pressure is generated in the thorax and air rushes in to fill the cavity. When that happens, these sacs fill with air, making the lung expand. The alveoli are rich with capillaries, called alveolar capillaries.
The contracting diaphragm pushes the abdominal organs downwards. But because the pelvic floor prevents the lowermost abdominal organs from moving in that direction, the pliable abdominal contents cause the belly to bulge outwards to the front and sides, because the relaxed abdominal muscles do not resist this movement (Fig. 7).
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]
The picture displays the mediastinum on sagittal plane, thoracic diaphragm at the bottom, the heart (cor), behind sternum and ribs (to the left on the picture (this is the anterior/front) and to the right (posterior/back)), you have the thoracic vertebrae.
For example, a subphrenic abscess beneath the right diaphragm might cause a patient to feel pain in the right shoulder. Irritation of the phrenic nerve (or the tissues it supplies) leads to the hiccup reflex. A hiccup is a spasmodic contraction of the diaphragm, which pulls air against the closed folds of the larynx.
The free edge of a ruptured diaphragm may curl and become perpendicular to the chest wall, a sign known as a dangling diaphragm. A herniated organ may constrict at the location of a rupture, a sign known as the collar sign. If the liver herniates through a rupture on the right side, it may produce two signs known as the hump and band signs.