The diaphragm is an unpaired, dome shaped skeletal muscle that is located in the trunk which separates the thoracic and abdominal cavities from each other by closing the inferior thoracic aperture. The diaphragm is the primary muscle that is active in inspiration. Contraction of the muscle facilitates expansion of the thoracic cavity. This increases volume of the the cavity, which in turn decreases the intrathoracic pressure allowing the lungs to expand and inspiration to occur.
As you can see, the diaphragm is much more than just a sheath separating your thoracic and abdominal cavities. This article will examine this intricate and crucial muscle in detail, looking at its attachments, innervation, and structures which pass through it.
Anteriorly: xiphoid process and costal margin
Laterally: 11th and 12th ribs
Posteriorly: lumbar vertebrae via the crura
|Relations||Pleural cavities, pericardial sac, liver, right kidney, right suprarenal gland, stomach, spleen, left kidney, left suprarenal gland|
Aortic hiatus (aorta, azygos vein, thoracic duct), esophageal hiatus (esophagus, vagus nerve), caval hiatus (inferior vena cava) - 'I ATE TEN EGGS AT 12'
Greater, lesser, least splanchnic nerves, superior epigastric vessels
|Functions||Primary muscle of breathing, especially during inspiration|
The diaphragm is a musculotendinous sheet. It has three muscular parts (sternal, costal, and lumbar), each have their own origin and all insert into the central tendon of diaphragm. The diaphragm is shaped as two domes, with the right dome positioned slightly higher than the left because of the liver. The depression between the two domes is due to the pericardium slightly depressing the diaphragm.
The diaphragm has two surfaces: thoracic and abdominal. The thoracic diaphragm is in direct contact with the lungs and pericardium, while the abdominal diaphragm is in direct contact with the liver, stomach, and spleen.
Since one function of the diaphragm is to provide passageway for structures from the thorax to the abdomen, its surface has several openings: caval opening (vena caval foramen), esophageal hiatus, and aortic hiatus.
Anatomically, you can define hiatus as an opening, slit, or gap that allows structures to pass. These openings in the diaphragm allow the inferior vena cava, esophagus, vagus nerves, descending aorta, and other structures to pass through.
An easy way to remember the location and structures passing through the diaphragm is by using this mnemonic: 'I ate ten eggs at 12.' - I (IVC) ate (T8) ten (T10) eggs (esophagus + vagus) at (azygos + thoracic duct) 12 (T12).
|Caval opening (vena caval foramen)||
Inferior vena cava
Branches of the right phrenic nerve
Anterior and posterior vagal trunks
There is a certain pathological condition called hiatal hernia, when part of the stomach protrudes from the abdomen into the thorax through the esophageal hiatus. You can learn more about this condition by reading this interesting clinical case.
Solidify your knowledge about the diaphragm, its surfaces, and openings by watching these videos and then quizzing yourself.
The diaphragm is one of the main muscles of respiration. When the muscle fibers contract, the diaphragm is flattened. This increases the volume of the thoracic cavity vertically, which decreases intrapulmonary pressure, and air enters the lungs.
When the diaphragm relaxes, thoracic volume decreases, intrapulmonary pressure increases, and air flows out of the lungs. Learn more about the anatomy of breathing and respiratory organs with these resources.
When the diaphragm works with the anterolateral abdominal muscles, diaphragm contraction assists in increasing intra-abdominal pressure. This is needed in actions such as expelling vomit, defecation, micturition (urination), and parturition (childbirth). Another function of the diaphragm is to provide a passageway for certain structures from the thorax to the abdomen (inferior vena cava, esophagus, and aorta) as mentioned earlier.
The diaphragm is a musculotendinous structure with a peripheral attachment to a number of bony structures. It is attached anteriorly to the xiphoid process and costal margin, laterally to the 11th and 12th ribs, and posteriorly to the lumbar vertebrae. The posterior attachment to the vertebrae is by tendinous bands called crura. The crura are attached to the anterior aspect of the bodies of the 1st, 2nd and 3rd lumbar vertebrae. The muscle fibres, extending from their bony attachments, converge on a central tendon.
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Motor innervation of the diaphragm comes from the phrenic nerves (C3-C5). These nerves innervate the diaphragm from its abdominal surface after they penetrate it. Sensory innervation (pain and proprioception) at the central tendinous part is innervated by the phrenic nerves, while the peripheral muscular portions are innervated by 6th to 11th intercostal nerves.
A very common disorder of the diaphragm that affects most people at some point is hiccups. Hiccups occur due to involuntary, intermittent contraction of the muscle. They are usually caused by consumption of large volumes of food over a short amount of time.
Herniation may occur through the diaphragm. At the level of the esophageal hiatus, the stomach may herniate into the posterior mediastinum. A diaphragmatic hernia can be congenital. These occur as a result of abnormalities in the development of the diaphragm in the fetus. Abdominal organs may protrude into the thoracic cavity and disrupt the development of the lungs, causing problems in lung development and the functioning of the lungs after birth.
Diaphragmatic hernias can also be acquired. These usually occur as a result of blunt force trauma, such as in a road traffic accident or a severe fall. Surgery is required to repair a diaphragmatic hernia.