Oxygen nutrients CO 2 . Forces are responsible. See book for detail. In general Hydrostatic pressure gradient favors filtration. Osmotic gradient favors reabsorption.
Net filtration occurs at the arterial end with net absorption occurring at the venous end.
Overall there is a small net filtration or loss of protein free fluid from the capillaries. This fluid is recaptured by the lymphatic circulation. Shifts in the distribution of fluid between the capillaries and the interstitium occur physiologically as in the response to plasma volume lose or hemorrhaging. The sympathetic nervous system can cause arteriolar constriction. This will lower the capillary hydrostatic pressure decreasing the driving force for filtration and promote reabsorption of fluid from the interstitium.