Usually the number of marks decides how much you should say buthere's the outline:
High blood pressure at the arterial end of a capillary forces fluid out into tissue, so forming tissue fluid. Excess tissue fluid that has not returned into capillaries at the venous end will drain into lymphatic vessels and form the lymph. Moreover, proteins in tissue fluid that are too large to enter capillaries can enter lymph vessels (this prevents oedema from occurring).
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