The urinary system or tract includes the kidneys, the ureters (tubes that connect the kidneys to the bladder), the bladder, and the urethra (the tube through which urine exits the body). The urinary system has several important functions. It gets rid of the waste products that are created when food is transformed into energy. It also maintains the correct balance of water and electrolytes (salts) within the body. Another key function is the production of hormones called erythropoietin and renin, which are important in maintaining healthy blood pressure, producing blood cells, and absorbing salt correctly. Finally, the urinary system processes vitamin D to its active form.