Anatomy of the Diaphragm

Diaphragm Structure

• The diaphragm is divided into a peripheral muscular part and a central tendinous part.
• The muscle fibers of the diaphragm arise from three parts: sternal, costal, and posterior vertebral or lumbar.
• The sternal part originates from the post surface of the xiphoid process and inserts into the central tendon.
• The costal part originates from the lower 6 ribs and costal cartilages and inserts into the central tendon.
• The posterior vertebral or lumbar part is divided into right and left crus, medial arcuate ligament, and lateral arcuate ligament.

Openings of the Diaphragm

• The diaphragm has several openings, including:
  • Aortic opening (T12): aorta, thoracic duct, and azygos vein
  • Esophageal opening (T10): esophagus, left and right vagus nerve, esophageal branch of left gastric vessels, and lymphatics from lower 1/3 of esophagus
  • Caval opening (T8): IVC, terminal branch of right phrenic nerve, and additional greater splanchnic nerve, lesser splanchnic nerve, and lowest splanchnic nerve

Innervation and Arterial Supply of the Diaphragm

• Motor innervation: phrenic nerves (C3, 4, 5)
• Sensory innervation: peripheral part (intercostal nerves T5-T11) and central part (phrenic nerve C3, 4, 5)
• Arterial supply: superior phrenic artery (branch of descending aorta), inferior phrenic artery (branch of abdominal aorta), pericardiacophrenic artery (branch of internal thoracic artery), and musculophrenic artery (branch of internal thoracic artery)

Actions of the Diaphragm

• Muscle of inspiration: pulls the central tendon down, increasing the vertical diameter
• Weight lifting muscle: takes a deep breath and fixes the diaphragm to rise the intra-abdominal pressure and support the vertebral column
• Muscle of abdominal straining: aids the contraction of anterior abdominal wall muscles and rises the intra-abdominal pressure to evacuate the pelvic content
• Thoraco-abdominal pump: descent of the diaphragm decreases the intra-thoracic pressure and increases the intra-abdominal pressure, compressing the blood in the IVC and forcing it upwards

Diaphragmatic Hernias

• Bochdalek's hernia: posterior
• Morgagni hernia: anterior

Relations of the Diaphragm

• Superior relations: pleura, base of the left and right lung, pericardium, and diaphragmatic surface of the heart
• Inferior relations: right lobe of the liver, right kidney, right suprarenal gland, left lobe of the liver, fundus of the stomach, left kidney, left suprarenal gland, and spleen