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Lymphatic vessels
Last reviewed: 06.07.2025
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Lymphatic vessels (vasa lymphatica) are formed by the fusion of lymphatic capillaries. The walls of lymphatic vessels are thicker than the walls of lymphocapillaries. Intraorgan and often extraorgan lymphatic vessels have only a thin connective tissue membrane (non-muscular vessels) outside the endothelium. The walls of larger lymphatic vessels consist of three membranes: the endothelium-covered inner membrane (tunica interna), the middle muscular membrane (tunica media), and the outer connective tissue membrane (tunica externa, s.adventitia).
Lymphatic vessels have valves (valvulae lymphaticае). The presence of valves gives these vessels a characteristic bead-like appearance). The valves of the lymphatic vessels, adapted to pass lymph in only one direction - from the "periphery" towards the lymph nodes, trunks and ducts, are formed by folds of the inner shell with a small amount of connective tissue in the thickness of each valve. Each valve consists of two folds of the inner shell (valve), located opposite each other. The distance between adjacent valves is from 2-3 mm in intraorgan lymphatic vessels to 12-15 mm in larger (extraorgan) vessels. Nearby intraorgan lymphatic vessels anastomose with each other, forming networks (plexuses), the loops of which have different shapes and sizes.
From the internal organs and muscles, the lymphatic vessels, as a rule, come out next to the blood vessels - these are the so-called deep lymphatic vessels (vasa lymphatica profunda). The superficial lymphatic vessels (vasa lymphatica superficialia), located outside the superficial fascia of the human body, are located next to the subcutaneous veins or near them. These vessels are formed from the lymphatic capillaries of the skin, subcutaneous tissue. In mobile places, in places of bends of the body (near joints), the lymphatic vessels bifurcate, forming roundabout (collateral) paths that ensure a continuous flow of lymph when the position of the body or its parts changes, as well as when the patency of some lymphatic vessels is impaired during flexion-extension movements in the joints.
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