Thoracic diaphragm
From Wikipedia, the free encyclopedia
| Diaphragm | |
|---|---|
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| Respiratory system | |
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| Under surface of the human diaphragm | |
| Latin | diaphragma |
| Gray's | subject #117 404 |
| Precursor | septum transversum |
| MeSH | A02.633.567.900.300 |
| Dorlands/Elsevier | d_15/12293509 |
- For other types of diaphragm, see Diaphragm.
In the anatomy of mammals, the diaphragm is a shelf of muscle extending across the bottom of the ribcage. The diaphragm separates the thoracic cavity (with lung and heart) from the abdominal cavity (with liver, stomach, intestines, etc.). In its relaxed state, the diaphragm is shaped like a dome. It is controlled by the phrenic nerve.
In order to avoid confusion with other types of diaphragm, it is sometimes referred to as the thoracic diaphragm. Any reference to the diaphragm is understood to refer to this structure.
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[edit] Function
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 external intercostals muscles 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 is also found in other vertebrates such as reptiles.
The diaphragm also helps to expel vomit, feces, and urine from the body by increasing intra-abdominal pressure.
[edit] Pathology
A hiatal hernia can result from a tear or weakness in the diaphragm near the gastroesophageal junction.
If the diaphragm is struck, or otherwise spasms, breathing will become difficult. This is called having the wind knocked out of you.
The diaphragm is sometimes deemed to consist of left and right hemidiaphragms. The two are visible as separate dome-like structures on chest X-ray. In addition, they are controlled separately by the left and right phrenic nerves; damage to one of these nerves leads to dysfunction or paralysis of the corresponding hemidiaphgram (and damage to both nerves can cause bilateral paralysis, severely impairing respiration).
A hiccup occurs when the diaphragm contracts periodically without voluntary control.
[edit] Anatomy
The Diaphragm is a dome-shaped musculofibrous septum which separates the thoracic from the abdominal cavity, its convex upper surface forming the floor of the former, and its concave under surface the roof of the latter. Its peripheral part consists of muscular fibers which take origin from the circumference of the thoracic outlet and converge to be inserted into a central tendon.
The muscular fibers may be grouped according to their origins into three parts:
| Part | Origin |
| sternal | two fleshy slips from the back of the xiphoid process. |
| costal | the inner surfaces of the cartilages and adjacent portions of the lower six ribs on either side, interdigitating with the Transversus abdominis. |
| lumbar | aponeurotic arches, named the lumbocostal arches, and from the lumbar vertebrae by two pillars or crura. |
There are two lumbocostal arches, a medial and a lateral, on either side.
[edit] Crura and central tendon
At their origins the crura are tendinous in structure, and blend with the anterior longitudinal ligament of the vertebral column.
The central tendon of the diaphragm is a thin but strong aponeurosis situated near the center of the vault formed by the muscle, but somewhat closer to the front than to the back of the thorax, so that the posterior muscular fibers are the longer.
[edit] Openings in the Diaphragm
The diaphragm is pierced by a series of apertures to permit of the passage of structures between the thorax and abdomen. Three large openings—the aortic, the esophageal, and the vena caval—and a series of smaller ones are described.
| opening | level | structures |
| caval opening | T8 | inferior vena cava, and some branches of the right phrenic nerve |
| esophageal hiatus | T10 | esophagus, the vagus nerves, and some small esophageal arteries |
| aortic hiatus | T12 | the aorta, the azygos vein, and the thoracic duct |
| two lesser aperture of right crus | greater and lesser right splanchnic nerves | |
| three lesser aperture of left crus | greater and lesser left splanchnic nerves and the hemiazygos vein | |
| behind the diaphragm, under the medial lumbocostal arches | gangliated trunks of the sympathetic | |
| areolar tissue between the sternal and costal parts | the superior epigastric branch of the internal mammary artery and some lymphatics from the abdominal wall and convex surface of the liver | |
| areolar tissue between the fibers springing from the medial and lateral lumbocostal arches | This interval is less constant; when this interval exists, the upper and back part of the kidney is separated from the pleura by areolar tissue only. |
The three main apertures can be remembered in order with the mnemonic "Come Enter the Abdomen" (caval, esophageal, and aortic).
[edit] Variations
The sternal portion of the muscle is sometimes wanting and more rarely defects occur in the lateral part of the central tendon or adjoining muscle fibers..
[edit] Additional images
 The phrenic nerve and its relations with the vagus nerve. |
 Thoracic portion of the sympathetic trunk. |
 Front view of the thoracic and abdominal viscera. |
 The duodenum and pancreas. |
 Topography of thoracic and abdominal viscera. |
 Organs of abdomen |
[edit] See also
[edit] External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.
