What does the thoracic duct do?

Function

The thoracic duct drains all of the lymph from the body below the diaphragm. It runs from the cisterna chyli, a retroperitoneal sac that collects lymph from the intestinal trunk and the two lumbar trunks. The thoracic duct passes posteriorly alongside the aorta and enters the thorax as the abdominal aorta passes through the aortic hiatus of the diaphragm. Within the thorax it passes alongside the oesophagus and empties into the venous system either at the left jugular or subclavian veins.

The thoracic duct transports filtered plasma proteins and excess tissue fluids back into the bloodstream. It transports lymph from all the body tissues below the diaphragm, except the right upper limb and some of the organs of the right hemithorax.

Most of the absorbed fat from the small intestines is transported in the lymphatic vessels first before entering the venous circulation. These lymphatics join to form the intestinal trunk which eventually empties into the thoracic duct. The thoracic duct also contains chyle, a milky fluid that is absorbed from digestion.

The lymph nodes on the thoracic duct help filter the lymph of various debris, bacteria, and pathogens. If any bacteria manages to escape into the bloodstream after passing the lymph nodes, the spleen may filter it out.