Kidney stones are made of salts and minerals in the urine that stick together to form small "pebbles." They are usually painless while they remain in the kidney, but they can cause severe pain as they break loose and travel through narrow tubes (ureters) to exit the body during urination. The kidneys are the master chemists of the body. Normally, there are two of them, one on either side of the spine under the lower ribs. They are reddish brown in colour and shaped like kidney beans. Each kidney is about the size of your clenched fist.

Kidney stones form when the components of urine — fluid and various minerals and acids — are out of balance. When this happens, your urine contains more crystal-forming substances, such as calcium and uric acid, than the available fluid can dilute. At the same time, your urine may be short of substances that keep crystals from sticking together and becoming stones. Kidney stones are also prone to develop in highly acidic or highly alkaline urine.

A kidney stone develops when substances in urine form crystals that stick together and grow in size. In most cases, these crystals are removed from the body by the flow of urine, but they sometimes stick to the lining of the kidney or settle in places where the urine flow fails to carry them away. These crystals may gather and grow into a stone, ranging in size from a grain of sand to a golf ball.

Diet plays an important role in the development of kidney stones, especially in patients who are predisposed to the condition. A diet high in sodium, fats, meat, and sugar, and low in fiber, vegetable protein, and unrefined carbohydrates increases the risk for renal stone disease. Recurrent kidney stones may form in patients who are sensitive to the chemical byproducts of animal protein and who consume large amounts of meat.

Calcium Stones: people who form this type of stone either have too much of one type of three chemicals in their urine, or not enough of another. In particular, they have either too much calcium, oxalate, or urate in their urine, or too little citrate. Eating too much salt may cause too much calcium to stay in the urine A few patients will have kidney stones from overproduction of the calcium controlling hormone, parathormone. Drinking milk does not cause kidney stones.

Uric acid stones: These stones are formed of uric acid, a byproduct of protein metabolism. You're more likely to develop uric acid stones if you eat a high-protein diet. Gout also leads to uric acid stones. Certain genetic factors and disorders of the blood-producing tissues also may predispose you to the condition.
Struvite Stones: This type of stone, also called an infection stone, develops when a urinary tract infection (e.g., bladder infection) affects the chemical balance of the urine. Bacteria in the urinary tract release chemicals that neutralize acid in the urine, which enables bacteria to grow more quickly and promotes struvite stone development.

Struvite stones are more common in women because they have urinary tract infections more often. The stones usually develop as jagged structures called "staghorns" and can grow to be quite large.

Cystine stones are formed by a build-up of cystine, combining with lysine, arginine and ornithine. Cystine stones account for 1 percent of all stones and are found in persons suffering from a hereditary disorder called cystinuria. Cystinuria occurs as a result of the kidney tubules not reabsorbing certain amino acids adequately. Cystine stones occur in both men and women equally.

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