Kidney Stones - Introduction

Introduction

Kidney stones are hard, solid particles that form in the urinary tract. In many cases, the stones are very small and can pass out of the body without any problems. However, if a stone (even a small one) blocks the flow of urine, excruciating pain may result, and prompt medical treatment may be needed.

Urine is formed in the kidneys. The kidneys filter out fluids and waste from the body, producing urine. As the urine passes through the kidneys, it becomes more concentrated. From the kidneys, urine flows through thin tubes called ureters into the bladder. The bladder's stretchy walls expand to store the incoming urine until it leaves the body through a tube called the urethra.

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The two kidneys are located deep behind the abdominal organs, below the ribs and toward the middle of the back.

Click the icon to see an image of the urinary tract.

Types of Kidney Stones

Occasionally, high levels of chemicals in the urine form into crystals. Eventually these crystals become large enough to form stones in the kidney, a condition called nephrolithiasis. Stones (calculi) may also form in the ureter or the bladder. Combinations of minerals and other chemicals, some derived from a person's diet, make up the salts in these stones.

Click the icon to see an image of the kidney stones.

Calcium Stones. About 70 - 90% of all kidney stones are made of calcium, usually combined with oxalate, or oxalic acid. A number of common vegetables, fruits, and grains contain oxalate.

About 6% of calcium stones are made of calcium phosphate (called brushite).

Uric Acid Stones. Uric acid is responsible for close to 10% of kidney stones. It is the breakdown product of purines, nitrogen compounds found in the body and in certain foods. Uric acid enters the bloodstream, and then passes primarily into the kidneys. From the kidneys, uric acid leaves the body in the urine. Often, uric acid stones occur with calcium stones.