Lymphatic valve

Lymphatic vessels are thin-walled endothelial channels that collect interstitial fluid from tissues and transport it as lymph toward the venous circulation, forming a unidirectional drainage system that integrates fluid balance with immune surveillance.

They begin as microscopic lymphatic capillaries, which are present in most tissues except the central nervous system, bone marrow, and avascular structures. These blind-ended capillaries consist of overlapping endothelial cells that function as one-way valves, allowing the entry of interstitial fluid and immune cells. From there, lymph flows into superficial lymphatic vessels located in the subcutaneous tissue, which accompany superficial veins and drain the skin and fascia. Deep lymphatic vessels, running alongside arteries and deep veins, drain muscles and internal organs. Both superficial and deep vessels converge into larger lymphatic trunks, which ultimately empty into the thoracic duct and the right lymphatic duct, draining into the left and right subclavian veins, respectively. Structurally, lymphatic vessels contain valves to maintain unidirectional flow and a layer of smooth muscle that contracts rhythmically to propel lymph. Functionally, they help maintain fluid balance, transport immune cells and antigens to lymph nodes, and absorb dietary fats in the form of chylomicrons via specialized intestinal lymphatic vessels called lacteals. Recently identified meningeal lymphatic vessels also contribute to interstitial fluid clearance in the central nervous system.

Clinical note: Obstruction of lymphatic vessels can lead to lymphedema.