Makindo Medical Notes

Anatomy of the Diaphragm

The diaphragm is a dome-shaped, musculotendinous structure that separates the thoracic cavity from the abdominal cavity. It plays a crucial role in respiration.

1. Structure

• Dome Shape: The diaphragm has a convex superior surface facing the thoracic cavity and a concave inferior surface facing the abdominal cavity.
• Central Tendon: The diaphragm consists of a central tendon where muscle fibres converge. The tendon is non-contractile and acts as the anchor for diaphragmatic muscle contractions.
• Muscle Portions:
  • Sternal Part: Attaches to the xiphoid process of the sternum.
  • Costal Part: Attaches to the inner surfaces of the lower six ribs and costal cartilages.
  • Lumbar Part: Anchors to the lumbar vertebrae through the right and left crura, which are extensions that help attach the diaphragm to the vertebral column.
• Openings:
  • Aortic Hiatus (T12): Allows passage of the aorta, thoracic duct, and azygos vein.
  • Oesophageal Hiatus (T10): Allows passage of the oesophagus and vagus nerves.
  • Caval Opening (T8): Allows passage of the inferior vena cava and some branches of the phrenic nerve.

2. Innervation

• The diaphragm is innervated by the phrenic nerve, which originates from the C3, C4, and C5 spinal nerves (C3, 4, 5 keep the diaphragm alive).
• It also receives some sensory innervation from the lower intercostal nerves.

3. Blood Supply

• Arterial Supply: Supplied by the superior phrenic artery (branch of the thoracic aorta), the musculophrenic artery, and the pericardiophrenic artery (branches of the internal thoracic artery).
• Venous Drainage: Drains into the brachiocephalic veins, azygos vein, and inferior vena cava.

Physiology of the Diaphragm

1. Role in Respiration

• The diaphragm is the primary muscle of respiration.
• Inhalation: During contraction, the diaphragm flattens, increasing the vertical dimension of the thoracic cavity, reducing intrathoracic pressure, and allowing air to flow into the lungs.
• Exhalation: During relaxation, the diaphragm returns to its dome shape, decreasing the thoracic cavity volume and forcing air out of the lungs.

2. Other Functions

• Pressure Regulation: The diaphragm also contributes to intra-abdominal pressure, aiding in functions such as defecation, urination, and childbirth.
• Oesophageal Function: The oesophageal hiatus, located in the diaphragm, helps prevent gastroesophageal reflux by acting as part of the lower oesophageal sphincter.