Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

Lymphatic VesselsThe function of the lymphatic vessels is to return lymph from the interstitial fluid 1 to the bloodcirculatory system where it may be purified and recharged with nutrients and oxygen. In general,lymphatic vessels resemble veins in structure, but have thinner walls, many more valves, and lymphnodes located at intervals along their course. The valves are usually semilunar pairs with free edgesin the direction of current flow. In case of blockage, the valves are often unable to withstand muchincrease in pressure and reverse (retrograde) flow may occur.Lymphatics originating in the villi (finger-like projections) of the small intestine are called lactealsand the fluid found in them after digestion is called chyle. 2 This fluid is milky in appearance fromabsorbed fats.The lymphatic capillaries originate as microscopic blind-end vessels which are located in theintercellular spaces and are widely distributed throughout the body. Small lymphatics merge withlarger ones and they, in turn, with still larger vessels until they join (much like the branches of a tree)to form the main lymphatic trunks: the right lymphatic duct and the thoracic duct. Lymph from theentire body, except the right upper quadrant, drains eventually into the thoracic duct which flows intothe left subclavian vein at the point where it joins the left internal jugular vein. Lymph from theupper right quadrant of the body empties into the right subclavian vein by way of the right lymphaticduct.Since most of the body lymph returns to the bloodstream via the thoracic duct, this vessel is muchlarger than the right lymphatic duct--but it is much smaller than the large veins which it resemblesin structure. The thoracic duct varies in length from 35 to 48 era. It originates as a dilated structure,the cisterna chyli, in the lumbar region of the abdominal cavity, and ascends by a winding course tothe root of the neck where it joins the left subclavian vein. Diagrammatic representation of lymphaticdrainage is shown for different parts of the body in Figures 8A and 8B.1interstitial fluid--The extra-cellular fluid which bathes the cells and is drained away as lymph.2chyle--The milky fluid taken up by the lacteals from the food in the small intestinedigestion. It passes into the thoracic duct at the cisterna chyli.during57