What chemical does the kidney release that produces urine?

The kidneys primarily produce urine through the filtration of blood, and one of the key hormones involved in this process is erythropoietin (EPO). However, EPO is primarily responsible for stimulating red blood cell production rather than urine formation. The actual urine production occurs through the filtration of blood plasma, reabsorption of water and solutes, and secretion of waste products. The final urine contains water, urea, creatinine, and various ions, but it is not directly produced by a single chemical released by the kidneys.