Diaphragmatic Openings and Nerves

Diaphragmatic Openings

• Two openings in the right crus: transmit greater and lesser splanchnic nerves
• Three openings in the left crus: transmit greater and lesser splanchnic nerves, and hemiazygous vein
• Opening for sympathetic trunks: under the medial arcuate ligament
• Opening for subcostal nerves and vessels: under the lateral arcuate ligament
• Opening for the left phrenic nerve: located in the left dome of the diaphragm

Movements of the Diaphragm

• The level of the domes of the diaphragm varies according to the phase of respiration, posture, and size and degree of distention of the abdominal viscera
• The diaphragm is the chief muscle of inspiration, and expiration is largely passive
• When the diaphragm contracts, its domes are pulled inferiorly, increasing the volume of the thoracic cavity and decreasing intrathoracic pressure, resulting in air being taken into the lungs

Movement of the Diaphragm and Circulation

• Movements of the diaphragm are also important in circulation
• When the diaphragm contracts, intra-abdominal pressure increases, and intrathoracic pressure decreases, compressing the abdominal viscera, widening the caval opening, and dilating the IVC

Crura of the Diaphragm

• The right crus is larger and longer than the left crus and can arise from the first three or four lumbar vertebrae
• The left crus can arise from the first two or three lumbar vertebrae
• Some of the muscle fibers of the right crus pass up to the left crus and surround the esophageal orifice in a sling-like loop, acting as a sphincter to prevent regurgitation of stomach contents into the thoracic part of the esophagus

Arcuate Ligaments of the Diaphragm

• The diaphragm is attached on each side to the medial and lateral arcuate ligaments
• The medial arcuate ligament is a thickening of the fascia covering the psoas major
• The lateral arcuate ligament is on the quadratus lumborum

Diaphragmatic Openings

• The diaphragm has three major openings: foramen for inferior vena cava, foramen for esophagus, and foramen for aorta
• Additional smaller openings include sternocostal triangle, openings for splanchnic nerves, hemiazygous vein, phrenic nerve, subcostal neurovascular structures, and sympathetic trunks

Neurovascular Supply of the Diaphragm

• Arterial supply: mainly from the inferior phrenic arteries, which arise directly from the abdominal aorta
• Venous drainage: superior surface of the diaphragm is drained by pericardiacophrenic and musculophrenic veins, and the right side is drained by the superior phrenic vein
• Innervation: motor nerve supply is by the right and left phrenic nerves (C3, 4, 5), and sensory nerve supply is by the phrenic nerve (C3-C5) and lower intercostal nerves (T5-T11) and subcostal nerves (T12)