As part of the lymphatic system, the thoracic duct is responsible for transporting nutrients and waste. It collects lymph from the two lower quadrants as well as the left upper quadrant of the body and returns it to the venous system. The thoracic duct directs lymph through lymph nodes, which are an important part of the immune system and provide information about possible diseases in the diagnostic process.
What is the thoracic duct?
The term ductus thoracicus is derived from the Latin word for duct and the Greek term for thorax. As the largest lymphatic trunk in the human body, it carries about three-quarters of all lymph from the two lower quadrants and the left upper quadrant of the body. The lymph is a pale yellow, watery fluid containing cells and lymphatic plasma. In German, the term Milchbrustgang is also used synonymously for the thoracic duct. This results from the milky, turbid quality of the lymph, which is produced after ingestion of food by the fats absorbed in the intestine. This fat-rich lymph is also referred to as chyle. The thoracic duct was first described medically in the 17th century in dogs, and a few years later in humans.
Anatomy and structure
The thoracic duct arises in the cisterna chyli, the lumbar cistern. This site is often dilated because the lymph of the lower extremities, pelvis, and abdomen converge here. The three lymphatic trunks leading from the lower quadrants of the body are the paired trunci lumbales and the unpaired truncus intestinalis. The thoracic duct receives the lymph from these three vessels before passing through the diaphragm on the right side behind the aorta. From there it passes upward along the spine through the thorax and then arcs in the neck to the left angle of the vein. The site of the orifice is located near the confluence of the internal jugular vein and subclavian vein to form the brachiocephalic vein. Just before the site of the orifice, the thoracic duct still receives the bronchomediastinal truncus, the subclavian truncus, and the jugular truncus. These three vessels collect the lymph of the left quadrant of the body. At the site of the orifice, a valve prevents venous blood from passing into the thoracic duct. Anatomically, the thoracic duct is similar to a blood vessel, but the lumen of the lymphatic vessels is larger for transporting proteins and clotted blood after injury
Function and Tasks
As part of the lymphatic vascular system, the thoracic duct complements the blood vascular system. It transports fluid that has not been reabsorbed by the blood vessels and returns it to the venous circulation. The lymphatic fluid in the thoracic duct transports proteins, fats, immune cells and water. After particularly high-fat meals, the fat concentration of the lymph is increased, causing the lymph to become cloudy and milky. In front of the mouth into the vein are lymph nodes, through which the thoracic duct conducts the lymph fluid. There it is cleansed of foreign bodies, tumor cells and pathogens. Lymph nodes are also an essential part of the human immune system. Depending on the presence of pathogens in the lymph fluid, they activate and multiply antibodies. These are subsequently released into the bloodstream to fight pathogens. If the activity is increased due to an infection or a tumor, the lymph node swells. This provides information about the presence and nature of the disease during medical examinations.
Diseases
Like all lymphatic vessels, the thoracic duct can be affected by congenital or acquired diseases. Lymphedema occurs when the reverse transport capacity is overwhelmed. The edema is an accumulation of fluid in the interstitial space. This can occur as a symptom of a concomitant disease such as right heart failure. Lymphangitis, colloquially known as sepsis, can also affect the ductus arteriosus. It is an inflammation of the lymph usually triggered by bacteria. The most externally conspicuous symptom is a red stripe on the skin emanating from the focus of inflammation. Enlarged lymph nodes appear in the corresponding area, and general symptoms such as fever may also occur. Chronic lymphangitis can also cause lymphedema over time due to a drainage disorder. Lymphangioma is similar to hemangioma in the vascular system.This is a rare, benign tumor disease. Lymphangioma usually occurs in early childhood, and is usually present at birth. Unlike hemangiomas, lymphangiomas do not regress on their own. Complete removal is required because recurrences form quickly if there is residue in the tissue. If the lymphangioma is not confined to a singular mass but is spread throughout the body, lymphangiomatosis is present. This disease causes the lymphatic vessels to proliferate into internal organs, bone, skin, or soft tissue. Lymphangiomatosis can result in fluid in the heart, abdominal cavity or lung cavity, as well as fever and internal bleeding. Other signs include massive pain and lymphedema. Prognosis depends largely on the location and spread of the disease. Lymphangiectasia also involves spindle-, sac-, or tube-shaped dilatation of the lymphatic vessels. It may be congenital as a concomitant of a syndrome or occur as part of an acquired disease. If rupture of the thoracic duct occurs due to trauma, lymphatic fluid leaks into the thoracic cavity. If several days of parenteral nutrition do not result in improvement, surgical repair of the rupture is required.
