Thoracic Duct: Anatomy and Function

Overview of the Thoracic Duct

• The thoracic duct is the largest lymphatic vessel in the body.
• Lymphatic vessels carry lymph throughout the body, similar to how blood vessels carry blood.
• There are two major lymphatic ducts: the thoracic duct and the right lymphatic duct.
• The thoracic duct carries approximately 75% of the body's lymph.
• The right lymphatic duct carries approximately 25% of the body's lymph.

Course and Location

• The thoracic duct extends from the upper abdomen to the lower neck.
• It crosses the posterior border and is superior to the mediastinum.
• The mediastinum is the space in the chest between the lungs, divided into superior and inferior parts.
• The thoracic duct originates from the cisterna chyli.
• Cisterna chyli is located in the upper part of the abdomen.
• The thoracic duct enters the thorax through the aortic opening of the diaphragm.
• It ascends through the posterior mediastinum and then the superior mediastinum.
• In the neck, the thoracic duct forms an arch.
• It drains into the junction between the left subclavian vein and the left internal jugular vein.
• The arch is located at the level of the seventh cervical vertebra.

Relations

• Relations of the thoracic duct are important to consider and can be divided into four areas: diaphragmatic, inferior mediastinal, superior mediastinal, and cervical (neck).
• General rule : the vertebral column is posterior in many regions, which is helpful to remember.

Relations on the Diaphragm

• Anterior: Diaphragm.
• Posterior: Vertebral column.
• Right: Azygos vein.
• Left: Aorta.

Relations in the Inferior Mediastinum

• Anterior: Esophagus.
• Posterior: Vertebral column.
• Right: Azygos vein.
• Left: Descending aorta.

Relations in the Superior Mediastinum

• Anterior: Aorta.
• Posterior: Vertebral column.
• Right: Pleura.
• Left: Pleura.

Relations in the Neck

• Anterior: Left common carotid artery.
• Posterior: Vertebral artery and vertebral column.

Tributaries

• The thoracic duct receives lymph from various tributaries before draining into the venous system.
• The following are tributaries that drain into the thoracic duct on it's left
  • Left jugular trunk.
  • Left subclavian trunk.
  • Left bronchomediastinal trunk.
• The three right equivalent trunks are the right jugular trunk, the right subclavian trunk, and the right bronchomediastinal trunk.

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