The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the circulatory system and the immune system. It is made up of a large network of lymph, lymphatic vessels, lymph nodes, lymphatic or lymphoid organs, and lymphoid tissues. The vessels carry a clear fluid called lymph towards the heart.
In human anatomy, the thoracic duct is the larger of the two lymph ducts of the lymphatic system. It is also known as the left lymphatic duct, alimentary duct, chyliferous duct, and Van Hoorne's canal. The other duct is the right lymphatic duct. The thoracic duct carries chyle, a liquid containing both lymph and emulsified fats, rather than pure lymph. It also collects most of the lymph in the body other than from the right thorax, arm, head, and neck. The thoracic duct usually starts from the level of the twelfth thoracic vertebrae (T12) and extends to the root of the neck. It drains into the systemic (blood) circulation at the junction of the left subclavian and internal jugular veins, at the commencement of the brachiocephalic vein.
The lymphatic vessels are thin-walled vessels (tubes) structured like blood vessels, that carry lymph. As part of the lymphatic system, lymph vessels are complementary to the cardiovascular system. Lymph vessels are lined by endothelial cells, and have a thin layer of smooth muscle, and adventitia that binds the lymph vessels to the surrounding tissue. Lymph vessels are devoted to the propulsion of the lymph from the lymph capillaries, which are mainly concerned with absorption of interstitial fluid from the tissues. Lymph capillaries are slightly larger than their counterpart capillaries of the vascular system. Lymph vessels that carry lymph to a lymph node are called afferent lymph vessels, and those that carry it from a lymph node are called efferent lymph vessels, from where the lymph may travel to another lymph node, may be returned to a vein, or may travel to a larger lymph duct. Lymph ducts drain the lymph into one of the subclavian veins and thus return it to general circulation.
The mediastinum is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esophagus, the trachea, the phrenic and cardiac nerves, the thoracic duct, the thymus and the lymph nodes of the central chest.
The periaortic lymph nodes are a group of lymph nodes that lie in front of the lumbar vertebrae near the aorta. These lymph nodes receive drainage from the gastrointestinal tract and the abdominal organs.
The right lymphatic duct is an important lymphatic vessel that drains the right upper quadrant of the body. It forms various combinations with the right subclavian vein and right internal jugular vein.
The tracheobronchial lymph nodes are lymph nodes that are located around the division of trachea and main bronchi.
The axillary lymph nodes or armpit lymph nodes are lymph nodes in the human armpit. Between 20 and 49 in number, they drain lymph vessels from the lateral quadrants of the breast, the superficial lymph vessels from thin walls of the chest and the abdomen above the level of the navel, and the vessels from the upper limb. They are divided in several groups according to their location in the armpit. These lymph nodes are clinically significant in breast cancer, and metastases from the breast to the axillary lymph nodes are considered in the staging of the disease.
The pararectal lymph nodes are lymph nodes that are in contact with the muscular coat of the rectum.
The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph nodes.
The jugular trunk is a lymphatic vessel in the neck. It is formed by vessels that emerge from the superior deep cervical lymph nodes and unite to efferents of the inferior deep cervical lymph nodes.
The superior deep cervical lymph nodes lie under the sternocleidomastoid muscle in close relation with the accessory nerve and the internal jugular vein.
Supraclavicular lymph nodes are lymph nodes found above to the clavicle, that can be felt in the supraclavicular fossa. The supraclavicular lymph nodes on the left side are called Virchow's nodes.
The submandibular lymph nodes, three to six in number, are lymph nodes beneath the body of the mandible in the submandibular triangle, and rest on the superficial surface of the submandibular gland.
The parasternal lymph nodes are placed at the anterior ends of the intercostal spaces, by the side of the internal thoracic artery.
The intercostal lymph nodes occupy the posterior parts of the intercostal spaces, in relation to the intercostal vessels.
The efferent vessels of the subclavicular group unite to form the subclavian trunk, which opens either directly into the junction of the internal jugular and subclavian veins or into the jugular lymphatic trunk; on the left side it may end in the thoracic duct.
The pretracheal lymph nodes are lymph nodes located anterior to the trachea in the neck.
Lymph trunk is a collection of lymph vessels that carries lymph, and is formed by confluence of many efferent lymph vessels. It in turn drains into one of the two lymph ducts.
The superior diaphragmatic lymph nodes lie on the thoracic aspect of the diaphragm, and consist of three sets – anterior, middle, and posterior.
