H OW DOES FILTRATE BECOME URINE ? As the filtrate passes through the renal tubule it is constantly changed based on the demands of the body. In order to maintain homeostasis it is necessary to reabsorb most filtered water, ions, glucose, and amino acids. It is also necessary to secrete drugs, toxins and some ions. The altered filtrate is excreted from the kidneys via the ureters to urinary bladder then out of the urethra as urine. Remember: when we are talking about secretion and reabsorption, the blood is our point of reference! We are secreting from the capillary INTO the renal tubule. We are reabsorbing into the capillary FROM the renal tubule.
M OVEMENT BETWEEN CAPILLARIES , INTERSTITIAL FLUID AND THE RENAL TUBULE . There are three basic types of transport that allow for secretion and reabsorption: