Anatomy of the Diaphragm

The Diaphragm

• The diaphragm is the principle muscle of respiration, forming the floor of the thoracic cavity and the roof of the abdominal cavity.
• It consists of a peripheral muscular part and a central tendinous part.

Relations of the Diaphragm

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

Parts of the Diaphragm

• Sternal part: originates from the posterior surface of the xiphoid process and inserts into the central tendon.
• Costal part: originates from the lower 6 ribs and costal cartilages and inserts into the central tendon.
• Posterior vertebral or lumbar portion:
  • Right crus: arises from the bodies of lumbar vertebrae 1-3 and the corresponding intervertebral discs.
  • Left crus: arises from the sides of the first two lumbar vertebrae and the corresponding intervertebral discs.
  • Medial arcuate ligament: connects the medial borders of the right and left crura.
  • Lateral arcuate ligament: extends from the tip of the transverse process of L1 to the lower border of the 12th rib.

Actions of the Diaphragm

• Muscle of inspiration: pulls the central tendon down, increasing the vertical diameter of the thoracic cavity.
• Weight lifting muscle: fixes the diaphragm to rise the intra-abdominal pressure, supporting the vertebral column and preventing flexion during lifting.
• Muscle of abdominal straining: aids the contraction of anterior abdominal wall muscles, rising the intra-abdominal pressure to evacuate the pelvic content.
• Thoraco-abdominal pump: descent of the diaphragm decreases intra-thoracic pressure, increasing intra-abdominal pressure, compressing blood in the IVC and forcing it upwards.

Openings of the Diaphragm

• Aortic Opening (T12): aorta, thoracic duct, and azygos vein.
• Esophageal Opening (T10): esophagus, left and right vagus nerves, esophageal branch of left gastric vessels, and lymphatics from the lower 1/3 of the esophagus.
• Caval Opening (T8): IVC, terminal branch of the right phrenic nerve.

Additional Features

• Greater, lesser, and lowest splanchnic nerves pierce the crura.
• Sympathetic trunk passes posterior to the medial arcuate ligament.
• Superior epigastric vessels pass between the sternal and costal portions of the diaphragm.
• Left phrenic nerve pierces the left dome of the diaphragm.

Weak Points of the Diaphragm

• Lumbocostal trigone
• Sternalcostal trigone
• Esophageal opening
• Aortic opening
• Caval opening

Arterial Supply of the Diaphragm

• Superior phrenic artery (branch of the descending aorta)
• Inferior phrenic artery (branch of the abdominal aorta)
• Pericardiacophrenic artery (branch of the internal thoracic artery)
• Musculophrenic artery (branch of the internal thoracic artery)

Innervation of the Diaphragm

• Motor innervation: phrenic nerves (C 3, 4, 5)
• Sensory innervation:
  • Peripheral part: intercostal nerves (T5-T11)
  • Central part: phrenic nerve (C3, 4, 5)

Diaphragmatic Hernias

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