Chest Wall, Diaphragm

Master answer

Anatomy of the Diaphragm

• Insertion
  • Anterior
    • Xiphoid process
    • Costal cartilage of ribs 6~12
  • Posterior
    • Lateral arcuate ligament (overlies quadratus lumborum)
    • Medial arcuate ligament (overlies psoas major)
    • Right and left crux (blends with anterior longitudinal ligament from vertebral bodies L1~3 on right, L1~2 on left)
    • Median arcuate ligament (between right and left crux, overlying aorta)
  • Central tendon – blends with pericardium superiorly and fibrous capsule of liver inferiorly
• Openings
  • Caval orifice (T8) – Within central tendon – Passage of the IVC
  • Oesophageal hiatus (T10) – Within sling of right crura – Passage of oesophagus and vagus nerve
  • Aortic hiatus (T12) – Posterior to median arcuate ligament between right and left crura – Passage of aorta, azygous vein and thoracic duct
• Innervation
  • Motor – Phrenic nerve (C3~5)
  • Sensory – Phrenic and inferior intercostal nerves
• Blood supply
  • Branches of the lower intercostal arteries, superior phrenic arteries
  • Inferior phrenic artery (branch of aorta) from inferior surface

Function of the Diaphragm

• On inspiration
  • Diaphragm contracts
    • Dome of diaphragm flattens and descends
    • Pushes lower thoracic ribs outwards
    • Increases AP diameter and superior-inferior distance of thorax → increased thoracic volume → Negative intrathoracic pressure → inspiration of air
    • Caval orifice dilates → increases venous return (Liver compressed squeezing hepatic blood reservoir, increased intraabdominal pressure due to descending diaphragm)
    • Aortic hiatus constricts → prevents arterial blood regurgitation
    • Oesophageal hiatus constricts → aids lower oesophageal sphincter and prevents regurgitation of gastric contents
• On expiration
  • Diaphragm relaxes
    • Elastic recoil of lung causes deflation and expiration

Sakurai 2016

Answer by Sakurai