Most people have two kidneys, whose main role in the body is to regulate fluid volume, maintain electrolyte balance, and remove waste products through the filtering of blood and production of urine. Formed urine collects and drains into minute collecting tubules, located in the renal pyramids. The urine exits kidney tissue from renal papilla, located at the ends of hollow structures known as calyxes. These calyxes join to become the larger space called a renal pelvis. The urine then moves down into ureters, small hollow tubes with smooth muscle which help to push urine down into the bladder. The connection between the renal pelvis and ureter is known as the ureteropelvic junction. The ureters enter into the bladder at connections known as the ureterovesical junction. The bladder then collects and stores the urine until it is convenient for a person to urinate, at which point the bladder will contract, expelling the urine out of the urethra.
Stones most commonly arise from within the kidney although they can also develop within the bladder or less commonly directly within the ureter.