The goal of urine production is to maintain homeostasis through regulating the volume and composition of blood. Involves the excretion of metabolic wastes. Three metabolic wastes, Urea, the most abundant organic waste; Creatinine, from the breakdown of creatine phosphate; and uric acid from the recycling of nitrogenous bases. Organic wastes dissolve in the bloodstream, eliminated only when dissolved in urine. Removal is accompanied by water loss.