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Development and age-related features of lymphatic vessels
Last reviewed: 06.07.2025
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The lymphatic system was first discovered in bony fish in the form of intestinal-mesenteric lymphatic vessels and their expansions - lymphatic sinuses between the internal organs, between the pericardium and gill sacs, near the fins. In amphibians and reptiles, contractile organs develop - lymphatic hearts, connecting on one side with the lymphatic sinuses and vessels, and on the other - with veins. In birds, lymphatic hearts are present only in the embryonic period; in waterfowl, lymph nodes (lumbar and cervical) appear for the first time. The number of lymph nodes increases in mammals, they develop valves in the lymphatic vessels.
In humans, at the 6th week of intrauterine development, slit-like spaces bounded by mesenchymal cells, which later transform into endothelial cells, are formed from the mesoderm separately from the circulatory system, but near the developing large veins. By merging the slit-like spaces, a system of channels is formed that grow and transform into lymphatic sacs. The right and left lymphatic sacs appear first, and somewhat later, the subclavian lymphatic sacs. A chain of sacs located near the dorsal wall of the embryo's body gives rise to the main lymphatic vessel - the thoracic duct, which opens into the left jugular sac at the 9th week of development. The jugular and subclavian lymphatic sacs located on the right and left connect with the veins in the neck. The lymphatic vessels of the pelvis and lower extremities develop from the paired iliac lymphatic sacs.
Age-related features of lymphatic vessels.
Lymphatic capillaries in newborns, as well as in adolescence and youth, have a comparatively larger diameter than in adults; the contours of the capillaries are smooth. Lymphatic capillaries form dense fine-meshed networks. In adults, lymphatic capillaries have a smaller diameter, become narrower, and some capillaries turn into lymphatic vessels. In the lymphatic networks, unclosed loops appear, as well as protrusions and swellings of the capillary walls. In old and senile age, the phenomena of lymphatic capillary reduction are expressed more clearly.
The lymphatic vessels of newborns and children in the first years of life have a characteristic bead-like pattern due to the presence of constrictions (narrowing) in the area of the valves, which are not yet fully formed. The valve apparatus of the lymphatic vessels reaches its maturity by 13-15 years of age.
In childhood and adolescence, adjacent lymphatic vessels are connected to each other by numerous transverse and obliquely oriented anastomoses, as a result of which lymphatic plexuses are formed around arteries, veins, and gland ducts. In people aged 40-50, signs of lymphatic vessel reduction appear. The contours of the vessels become uneven, in places there are protrusions of the walls, the number of anastomoses between the lymphatic vessels decreases, especially between the superficial and deep ones. Some vessels become empty. The walls of the lymphatic vessels in elderly and senile people thicken, their lumen decreases.
The thoracic duct in newborns and older children is correspondingly smaller in size than in an adult, its walls are thin. The thoracic duct reaches its maximum development in adulthood. In elderly people and old people, connective tissue grows in the walls of the thoracic duct with some atrophy of the smooth (involuntary) muscles.
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