Lungs and Ventilation Pathway LO5

5. Describe the basic structure of the diaphragm, and identify its neurovascular supply.

The diaphragm is the muscular division between the thoracic and abdominopelvic cavities. The muscular fibers of the diaphragm originate circumferentially from the thoracic outlet/inferior thoracic aperture (an uneven ring following the inferior margins of the 11th and 12th ribs, the costal cartilages, and the xiphisternal junction), and insert on the central tendon.

There are 3 major apertures of the diaphragm:

    • Caval opening (at T8)
        • Contents: inferior vena cava, right phrenic n., & lymphatics
    • Esophageal hiatus (at T10)
        • Contents: esophagus, anterior & posterior vagal trunks, esophageal branch of left gastric a., & lymphatics
    • Aortic hiatus (at T12)
        • Contents: descending aorta, thoracic duct, & branch of the azygos v.

There are 2 smaller, bilateral hiatuses within the crura that transmit the greater and lesser splanchnic nerves.

Innervation: The phrenic nn. provide efferent innervation to the diaphragm ("C3, 4, & 5 keep the diaphragm alive"), while afferent innervation is distributed by the phenic nn. and the 6th-7th intercostal nn.

Vascular supply: The dominant blood supply to the diaphragm is from the inferior phrenic aa., but also receives supply from the superior phrenic aa., inferior 5 intercostal aa., and the subcostal aa.