Kidney stones are mineral and acid salt deposits that clump together in concentrated urine. They can cause discomfort when moving through the urinary tract, but they rarely cause long-term damage. A kidney stone can sometimes pass through the ureter, the tube that connects the kidney with the bladder. If the stone reaches the bladder, it can be transported through the urine and out of the body. If a stone becomes trapped in the ureter, it causes pain by blocking urine flow from that kidney.
Kidney stones form when dissolved minerals build up on the inner lining of the kidneys. They are usually made up of calcium oxalate, although they can also be made up of a variety of other chemicals. These stones can grow up to the size of a golf ball while keeping a sharp, crystalline structure. The stones may be small and go unnoticed while they transit through the urinary tract, but once they exit the body, they can cause intense pain.