The lymphatic system is part of the vascular system and an important part of the immune system, composed of a large network of lymphatic vessels that carry a clear fluid called lymph directionally towards the heart. The lymphatic system was first described in the seventeenth century independently by Olaus Rudbeck and Thomas Bartholin. Unlike the circulatory system, the lymphatic system is not a closed system. The human circulatory system processes an average of 20 litres of blood per day through capillary filtration, which removes plasma while leaving the blood cells. Roughly 17 litres of the filtered plasma is reabsorbed directly into the blood vessels, while the remaining three litres remain in the interstitial fluid. One of the main functions of the lymph system is to provide an accessory return route to the blood for the surplus three litres.
A lymph node or lymph gland is an ovoid or kidney-shaped organ of the lymphatic system and the adaptive immune system. Lymph nodes are widely present throughout the body and are linked by the lymphatic vessels. They are major sites of B and T cells and other white blood cells. Lymph nodes are important for the proper functioning of the immune system, acting as filters for foreign particles and cancer cells, but they do not have a detoxification function.
Lymph is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to the central circulation. Interstitial fluid – the fluid which is between the cells in all body tissues – enters the lymph capillaries. This lymphatic fluid is then transported via progressively larger lymphatic vessels through lymph nodes, where substances are removed by tissue lymphocytes and circulating lymphocytes are added to the fluid, before emptying ultimately into the right or the left subclavian vein, where it mixes with central venous blood.
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.
Lymphadenopathy or adenopathy is disease of the lymph nodes, in which they are abnormal in size or consistency. Lymphadenopathy of an inflammatory type is lymphadenitis, producing swollen or enlarged lymph nodes. In clinical practice, the distinction between lymphadenopathy and lymphadenitis is rarely made and the words are usually treated as synonymous. Inflammation of the lymphatic vessels is known as lymphangitis. Infectious lymphadenitis affecting lymph nodes in the neck is often called scrofula.
Lymphadenectomy or lymph node dissection is the surgical removal of one or more groups of lymph nodes. It is almost always performed as part of the surgical management of cancer. In a regional lymph node dissection, some of the lymph nodes in the tumor area are removed; in a radical lymph node dissection, most or all of the lymph nodes in the tumor area are removed.
Inguinal lymph nodes are lymph nodes in the human groin. Located in the femoral triangle of the inguinal region, they are grouped into superficial and deep lymph nodes. The superficial have three divisions: the superomedial, superolateral, and inferior superficial.
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 external iliac lymph nodes are lymph nodes, from eight to ten in number, that lie along the external iliac vessels.
The tracheobronchial lymph nodes are lymph nodes that are located around the division of trachea and main bronchi.
Cervical lymph nodes are lymph nodes found in the neck. Of the 800 lymph nodes in the human body, 300 are in the neck. Cervical lymph nodes are subject to a number of different pathological conditions including tumours, infection and inflammation.
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 preaortic lymph nodes lie in front of the aorta, and may be divided into celiac lymph nodes, superior mesenteric lymph nodes, and inferior mesenteric lymph nodes groups, arranged around the origins of the corresponding arteries.
The inferior mesenteric lymph nodes consist of:
The internal iliac lymph nodes surround the internal iliac artery and its branches, and receive the lymphatics corresponding to the distribution of the branches of it, i. e., they receive lymphatics from all the pelvic viscera, from the deeper parts of the perineum, including the membranous and cavernous portions of the urethra, and from the buttock and back of the thigh. The internal iliac lymph nodes also drain the superior half of the rectum, above the pectinate line.
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 celiac lymph nodes are associated with the branches of the celiac artery. Other lymph nodes in the abdomen are associated with the superior and inferior mesenteric arteries. The celiac lymph nodes are grouped into three sets: the gastric, hepatic and splenic lymph nodes.
Lymphography is a medical imaging technique in which a radiocontrast agent is injected, and then an X-ray picture is taken to visualize structures of the lymphatic system, including lymph nodes, lymph ducts, lymphatic tissues, lymph capillaries and lymph vessels. Lymphangiography is the same procedure, used only to visualize the lymph vessels. The X-ray film or image of the vessels and nodes is called a lymphogram or a lymphangiogram.
