The kidneys primarily filter blood and produce urine in the human body.
Most people have two kidneys, located toward the back of the abdominal cavity on either side of the spine. Each kidney contains many nephrons, which filter blood and then selectively reabsorb water and useful dissolved substances while secreting additional wastes into the forming urine.
Urine passes from each kidney through a ureter to the urinary bladder, where it is stored before leaving through the urethra. The kidneys also help regulate blood pressure, acid–base balance, electrolyte levels, and the body's water content. They release hormones involved in red-blood-cell production and calcium metabolism.
The liver also processes substances in the blood and makes bile, but it does not produce urine. The spleen filters blood cells and supports immunity, while the pancreas produces digestive enzymes and hormones. These organs have important filtering or regulatory roles, but they are not the urinary organs.