Thoracic diaphragm

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Diaphragm
Respiratory system
Latin	diaphragma
Gray's	subject #117 404
Artery	Pericardiacophrenic artery, Musculophrenic artery, Inferior phrenic arteries
Vein	Superior phrenic vein, Inferior phrenic vein
Nerve	phrenic and lower intercostal nerves
Precursor	septum transversum, pleuroperitoneal folds, body wall [1]
MeSH	Diaphragm
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 abdominopelvic 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.

Contents 1 Function 2 Pathology 3 Anatomy 3.1 Crura and central tendon 3.2 Openings in the Diaphragm 3.3 Variations 4 Additional images 5 See also 6 References 7 External links

[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.

Diaphragmatic injuries result from either blunt or penetrating trauma. A traumatic diaphragmatic rupture is more commonly diagnosed on the left side, perhaps because the liver obliterates the defect or protects it on the right side. In addition, the appearance of bowel, stomach or a nasogastric (NG) tube is more easily detected in the left side of the chest. Right diaphragmatic ruptures are rarely diagnosed in the early post-injury period. The liver often prevents herniation of other abdominal organs into the chest. This, however, may not be representative of the true incidence of laterality and autopsy studies have revealed that left- and right-sided ruptures occur almost equally. Blunt trauma produces large radial tears measuring 5–15 cm, most often at the posterolateral aspect of the diaphragm. In contrast, penetrating trauma usually create only small linear incisions or perforations, which are less than 2 cm in size and may often take some time, even years, to develop into diaphragmatic hernias. If a laceration of the left diaphragm is suspected, a NG tube should be inserted. If the tube appears in the thoracic cavity on the chest film, the need for special contrast studies can be eliminated. Minimally invasive endoscopic procedures (thoracoscopy) may be helpful in evaluating the injury to the diaphragm in indeterminate cases. Abdominal computed tomography scan is usually not helpful because of its poor visualisation of the diaphragm. Magnetic resonance imaging is more accurate in visualising the anatomy of the diaphragm. It is very sensitive and specific and so is the investigation of choice. Surgical repair is necessary, even for small tears, because the defect will not heal spontaneously.

[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 cava—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 (see also foramina of Morgagni)		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

Inferior view of the human diaphragm	The phrenic nerve and its relations with the vagus nerve.	Plan of right sympathetic cord and splanchnic nerves.	Thoracic portion of the sympathetic trunk.
The position and relation of the esophagus in the cervical region and in the posterior mediastinum. Seen from behind.	Front view of the thoracic and abdominal viscera.	The duodenum and pancreas.	Topography of thoracic and abdominal viscera.
Organs of abdomen	Peritoneopericardial diaphragmatic hernia in a cat.	Hiatal hernia	Probably the first dictionary definition of "diaphragm"

[edit] See also

• midriff

[edit] References

1. ^ Embryology at UNC mslimb-012

[edit] External links

• GPnotebook 483393594
• LUC dph

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.