<P> Lymphatic capillaries are slightly larger in diameter than blood capillaries , and have closed ends ( unlike the loop structure of blood capillaries ) . Their unique structure permits interstitial fluid to flow into them but not out . The ends of the endothelial cells that make up the wall of a lymphatic capillary overlap . When pressure is greater in the interstitial fluid than in lymph , the cells separate slightly , like the opening of a one - way swinging door , and interstitial fluid enters the lymphatic capillary . When pressure is greater inside the lymphatic capillary , the cells adhere more closely , and lymph can not escape back into interstitial fluid . Attached to the lymphatic capillaries are anchoring filaments , which contain elastic fibers . They extend out from the lymphatic capillary , attaching lymphatic endothelial cells to surrounding tissues . When excess interstitial fluid accumulates and causes tissue swelling , the anchoring filaments are pulled , making the openings between cells even larger so that more fluid can flow into the lymphatic capillary . </P>
when do anchoring filaments open spaces between endothelial cells in lymph capillaries
When excess interstitial fluid accumulates and causes tissue swelling