Question

briefly describe where lnterstitial fluid comes from

Answer 1

Lymph is the fluid that circulates throughout the lymphatic system. The lymph is formed when the interstitial fluid (the fluid which lies in the interstices of all body tissues)[1] is collected through lymph capillaries. It is then transported through lymph vessels to lymph nodes before emptying ultimately into the right or the left subclavian vein, where it mixes back with blood.
http://en.wikipedia.org/wiki/Lymph