decides where the process will happen, first the blood enters the kidney by the renal artery by the capillaries, then the blood pressure forces so,some of the water and dissolved substances in the blood to cross the capillary walls into bowman’s capsule. Once in there the fluid passes to a collecting duct, which reabsorbs some water and returns it to the bloodstream, then in the renal tubule some of the filtered substances are reabsorbed and returned to the bloodstream, all of the substances in fluid the remain in the collecting duct is urine.