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Diaphragm: want to learn more about it?

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Diaphragm

The diaphragm is an unpaired, dome shaped skeletal muscle that is located in the trunk. It 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.

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 anatomy, function and structures which pass through it.

Key facts about the diaphragm
Origin Sternal part: Posterior aspect of xiphoid process
Costal part: Internal surfaces of lower costal cartilages and ribs 7-12
Lumbar part: Medial and lateral arcuate ligaments (lumbocostal arches), bodies of vertebrae L1-L3 (+intervertebral discs), anterior longitudinal ligament
Insertion Central tendon of diaphragm
Relations Pleural cavities, pericardial sac, liver, right kidney, right suprarenal gland, stomach, spleen, left kidney, left suprarenal gland
Openings Aortic hiatus (aorta, azygos vein, thoracic duct), esophageal hiatus (esophagus, vagus nerve), caval hiatus (inferior vena cava)
Mnemonic: I 8 10 EGGS AT 12
Greater, lesser, least splanchnic nerves, superior epigastric vessels
Innervation Phrenic nerves (C3-C5) (sensory innervation of peripheries via 6th-11th intercostal nerves)
Mnemonic:  C3, 4, 5 keeps the diaphragm alive!
Blood supply Subcostal and lowest 5 intercostal arteries, inferior phrenic arteries, superior phrenic arteries
Functions Depresses costal cartilages, primary muscle of breathing (inspiration)

Origin and insertion

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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Structure and relations

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. 

Thoracic surface of the diaphragm (diagram)

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.

Abdominal surface of the diaphragm (diagram)

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.

Abdominal surface of the diaphragm in a cadaver: The esophageal hiatus passes through the right crus of the diaphragm. The foramen of the inferior vena cava traverses through the central tendon, while the aortic hiatus passes behind the diaphragm.

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. 

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Mnemonic

An easy way to remember the location and structures passing through the diaphragm is by using this mnemonic: 'I 8 10 EGGs AT 12' (read: I ate ten eggs at twelve).

I 8 - IVC crosses the diaphragh at the level of T8

10 EGGs - EsophaGus + vaGus cross the diaphragh at the level of T10

AT 12 - Aorta + Azygos vein + Thoracic duct cross the diaphragm at the level of T12

Openings of the diaphragm and structures passing through
Caval opening (vena caval foramen) Inferior vena cava
Branches of the right phrenic nerve
Esophageal hiatus
Anterior and posterior vagal trunks, esophagus
Aortic hiatus Descending aorta
Azygos vein
Thoracic duct

Solidify your knowledge about the diaphragm, its surfaces, and openings by using these resources:

Innervation

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.

Mnemonic

Perhaps the most well known mnemonic amongst anatomy students actually concerns the innervation of the diaphragm. Learn ' C3, 4, 5 keeps the diaphragm alive!' and you will never forget the motor innervation again!

Learn more about the diaphragm anatomy with our custom quiz which covers the anatomy, blood supply, innervation and function of the diaphragm!

Blood supply

The respiratory diaphragm is a large complex muscle and thus its blood supply comes from various arteries. The costal margin of the diaphragm are supplied by the subcostal arteries and the five most inferior pairs of intercostal arteries.

Inferior phrenic arteries are closely related to the diaphragm and give off a few branches to supply it. They are the main source of vascular supply to the diaphragm. The left inferior phrenic artery ascends toward the left diaphragmatic crus associated with the inferior surface of the diaphragm. From here is passes posterior to the esophagus and runs anteriorly along the edge of the esophageal hiatus. The right passes behind the IVC and anteriorly along the vena cava hiatus. Each artery gives of medial branches, which anastomose with each other, musculophrenic and cardiophrenic arteries, and lateral branches, which inferior posterior intercostal and musculophrenic arteries, close to the thoracic wall.

The final source of blood supply are superior phrenic arteries. They supply the superior surface of the diaphragm.

Function

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.

Diaphragm: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

What do you prefer to learn with?

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

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