how kidney stones develop?

The urinary tract is composed of two kidneys and ureters, a bladder, and a urethra (figure 1). A kidney stone usually forms when substances that are normally found in the urine, such as calcium, oxalate, cystine, or uric acid, are at high levels. However, in some children, stones can also form if these substances are at normal levels. Knowing what the stone is made of is important in deciding which treatment to use. (See 'Stone testing' below.)
The substances form crystals, which become anchored in the kidney and gradually increase in size, forming a kidney stone. Stones that are very small (less than 5 millimeters [0.2 inches]) can usually pass on their own, while larger stones usually require treatment.
A kidney stone moves through the urinary tract and, if it is small enough, it will be passed in the urine. A larger stone can become stuck within the urinary tract, causing pain and sometimes blocking the flow of urine
What causes kidney stones in children?
Kidney stones can form when substances in the urine—such as calcium, magnesium, oxalate, and phosphorous—become highly concentrated due to one or more causes:
· Defects in the urinary tract may block the flow of urine and create pools of urine. In stagnant urine, stone-forming substances tend to settle together into stones. Up to one-third of children who have stones have an anatomic abnormality in their urinary tract.
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