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Structure

Diaphragm

Not medically reviewed · Content last updated · 2 min read ·

This is the date the draft was written, not a medical review date.

The diaphragm is a dome-shaped musculotendinous sheet that separates the thoracic and abdominal cavities. It is the principal muscle of inspiration.

Terminologia Anatomica (Latin): Diaphragma · Open in the 3D atlas

Location

It attaches to the xiphoid process, the lower six costal cartilages and ribs, and the lumbar vertebrae through the crura. The right dome normally lies slightly higher than the left, reaching about the level of the fifth intercostal space in quiet expiration.

Structure

A central tendon is surrounded by muscle fibres of sternal, costal and lumbar parts; the right crus arises from L1 to L3 and the left from L1 to L2, and the median arcuate ligament crosses the aorta. The caval opening (about T8) transmits the inferior vena cava and right phrenic branches, the oesophageal hiatus (about T10) the oesophagus and vagal trunks, and the aortic hiatus (about T12) the aorta, thoracic duct and often the azygos vein.

Blood supply

The superior surface is supplied by the pericardiacophrenic and musculophrenic arteries and the superior phrenic arteries, and the inferior surface mainly by the inferior phrenic arteries from the abdominal aorta, with contributions from the lower intercostal arteries.

Innervation

Motor supply, and sensation from the central part, come from the phrenic nerve (C3 to C5); the peripheral part receives sensory fibres from the lower intercostal and subcostal nerves. Irritation of the central diaphragm is therefore referred to the shoulder tip (C4 dermatome).

Function

On contraction the domes descend and flatten, increasing the vertical dimension of the thorax and lowering intrathoracic pressure to draw air in; expiration at rest is passive. It also raises intra-abdominal pressure during cough, defecation and parturition and helps to prevent gastro-oesophageal reflux.

Clinical correlations

Hiatus hernia involves herniation of the stomach through the oesophageal hiatus, and congenital diaphragmatic hernia (most often posterolateral, Bochdalek, on the left) causes pulmonary hypoplasia. Phrenic nerve injury produces an elevated, paralysed hemidiaphragm, and irritation of the diaphragm by subphrenic or pleural disease causes shoulder-tip pain. Hiccup results from spasmodic diaphragmatic contraction.

Common exam points

  • Apertures: caval opening T8 (IVC, right phrenic branches), oesophageal hiatus T10 (oesophagus, vagal trunks), aortic hiatus T12 (aorta, thoracic duct, azygos vein).
  • Motor and central sensory supply by the phrenic nerve (C3, C4, C5): C3, 4, 5 keep the diaphragm alive.
  • Peripheral sensation from lower intercostal and subcostal nerves; central irritation refers pain to the shoulder tip.
  • Right crus arises from L1 to L3, left crus from L1 to L2; median arcuate ligament lies over the aorta.
  • Hiatus hernia and Bochdalek hernia are the key herniations; phrenic palsy elevates the hemidiaphragm.

References

  1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. Elsevier — Tier 3 (textbook)
  2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. Wolters Kluwer, 8th edition (2018) — Tier 3 (textbook)
  3. Hall JE, Hall ME. Guyton and Hall Textbook of Medical Physiology. Elsevier, 14th edition (2020) — Tier 3 (textbook)

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