Diaphragm

Function

The diaphragm is the engine of breathing: a musculotendinous dome whose contraction flattens it by 1.5 cm in quiet breathing (up to 7 cm in deep breaths), dropping intrathoracic pressure to draw ~500 ml of air into the lungs while raising intra-abdominal pressure — the same action that powers coughing, defecation and childbirth.

It works continuously: the two phrenic nerves (C3–C5) drive it about 20,000 times a day. Its openings conduct the IVC at T8, the oesophagus with vagal trunks at T10, and the aorta with the thoracic duct at T12 — the landmarks of abdominal level-keeping.

Blood supply

Pericardiacophrenic, musculophrenic and inferior phrenic arteries.

Nerve supply

Phrenic nerve (C3, C4, C5 — 'keep the diaphragm alive'); peripheral costal fibres share intercostal supply.

Clinical relevance

Hiatus hernia

The oesophageal hiatus widens with age and pressure, letting the stomach slide into the chest — reflux follows.

Diaphragmatic rupture

Blunt trauma tears the dome, usually on the left (the liver shields the right); late herniation of bowel strangulates.

Phrenic nerve palsy

The hemidiaphragm rises and paradoxically ascends on inspiration — sniff fluoroscopy reveals it.