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The lymphatic system, or lymphoid system, is an organ system in vertebrates that is part of the immune system and complementary to the circulatory system.It consists of a large network of lymphatic vessels, lymph nodes, lymphoid organs, lymphatic tissue and lymph.
Lymph (from Latin lympha ' water ') [1] 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 be recirculated.
The lymph percolates through the lymph node tissue and exits via an efferent lymph vessel. An efferent lymph vessel may directly drain into one of the (right or thoracic) lymph ducts, or may empty into another lymph node as its afferent lymph vessel. [6] Both the lymph ducts return the lymph to the blood stream by emptying into the subclavian veins
Lymph enters the convex side of a lymph node through multiple afferent lymphatic vessels, and from there, it flows into a series of sinuses. Upon entering the lymph node, lymph first passes into a space beneath the capsule known as the subcapsular sinus , then moves into the cortical sinuses .
In peripheral organs, lymphatic vessels are responsible for conducting lymph between different parts of the body. In general, lymphatic drainage is important for maintaining fluid homeostasis as well as providing a means for immune cells to traffic into draining lymph nodes from other parts of the body, allowing for immune surveillance of bodily tissues.
The lymph transport, in the thoracic duct, is mainly caused by the action of breathing, aided by the duct's smooth muscle and by internal valves which prevent the lymph from flowing back down again. There are also two valves at the junction of the duct with the left subclavian vein, to prevent the flow of venous blood into the duct.
Upon entering the lumen of a lymphatic capillary, the collected fluid is known as lymph. Each lymphatic capillary carries lymph into a lymphatic vessel, which in turn connects to a lymph node, a small bean-shaped gland that filters and monitors the lymphatic fluid for infections. [1] Lymph is ultimately returned to the venous circulation.
When an efferent lymph vessel leaves a lymph node, it may carry lymph to another lymph node by becoming its afferent lymph vessel or unite with other efferent vessels to become a lymph trunk. The lymph trunks drain into the lymph ducts, which in turn return lymph to the blood by emptying into the respective subclavian veins. [1]