What is a kidney stone? What causes kidney stones?

What is a kidney stone?

A kidney stone is a small stone, usually made up of calcium crystals, that forms inside the part of the kidney where urine collects. The stone usually causes little problem until it falls into the ureter, the tube that drains the kidney into the bladder, and causes an obstruction, preventing urine from draining out of the kidney and often causing severe pain.

One of the roles of the kidney is to remove waste from the body by filtering blood and making urine. That urine flows from the kidney into the bladder through the ureter, a thin tube that connects the two. The bladder empties through the urethra, a tube much wider than the ureter.

A variety of minerals and chemicals are excreted in the urine and sometimes these combine to form the beginning of a stone. Over time, this can grow from an invisible speck of sand into a stone that can be an inch in diameter or larger.

There are different terms for kidney stones depending upon where they are located within the urinary tract:

Urolith: A stone anywhere within the urinary tract
Nephrolith: A stone within the kidney
Ureterolith: A stone within the ureter
Calculus: A stone within the body

What causes kidney stones?

It isn't exactly clear what causes kidney stones to form in some people and not others. Usually it requires concentrated urine that allows minerals like calcium to come in close contact with each other. Changes in the acid-base balance (pH) of the urine, how concentrated it is, and the concentration of minerals and chemicals within the urine are all factors that can begin the formation of a stone.

Crystals can form the beginning of the stone and eventually grow large enough to cause problems. Concentrated urine often occurs during an episode of dehydration, setting the stage for the beginning of stone formation. The consequences of that stone, when it is large enough to cause an obstruction, may occur weeks, months, or years later..