The lymphatic circulation begins with blind ending (closed at one end) highly permeable superficial lymph capillaries, formed by endothelial cells with button - like junctions between them that allow fluid to pass through them when the interstitial pressure is sufficiently high. These button - like junctions consist of protein filaments like platelet endothelial cell adhesion molecule - 1, or PECAM - 1. A valve system in place here prevents the absorbed lymph from leaking back into the ISF. There is another system of semilunar (semi = half; lunar = related to the Moon) valves that prevents back - flow of lymph along the lumen of the vessel. Lymph capillaries have many interconnections (anastomoses) between them and form a very fine network.
structure that prevents backflow of fluid in lymphatic vessels
A valve system