Kidney stones are hard objects, made up of millions of tiny crystals.
Most kidney stones form on the interior surface of the kidney, where
urine leaves the kidney tissue and enters the
urinary collecting system. Kidney stones can be small,
like a tiny pebble or grain of sand, but often are much larger.
The job of the kidneys is to maintain the body's
balance of water, minerals and salts. Urine is the product of this
filtering process. Under certain conditions, substances normally
dissolved in urine such as calcium, oxalate, and phosphate, become
too concentrated and can separate out as crystals. A kidney stone
develops when these crystals attach to one another, accumulating
into a small mass, or stone.
Kidney stones come in a variety of mineral types.
stones are composed of calcium and oxalate. Many people who
form calcium containing stones have too much calcium in their
urine, a condition known as hypercalciuria
There are several reasons why hypercalciuria may occur. Some
people absorb too much calcium from their intestines. Others
absorb too much calcium from their bones. Still others have
kidneys which do not correctly regulate the amount of calcium
they release into the urine. There are some people who form
calcium oxalate stones as a result of too much oxalate in the
urine, a condition known as hyperoxaluria
In some cases, too much oxalate in the urine is a result of
inflammatory bowel disease, such as Crohn's disease or ulcerative
colitis, or other times it may be a consequence of prior intestinal
surgery. Calcium phosphate stones, another kind of calcium stone,
are much less common than calcium oxalate stones. For some people,
calcium phosphate stones form as a result of a medical condition
known as renal tubular acidosis.
Struvite Stones: Some patients
form stones that are composed of a mixture of magnesium, ammonium,
phosphate, and calcium carbonate, which is known as struvite.
These stones form as a result of infection with certain types
of bacteria that can produce ammonia. Ammonia acts to raise
the pH of urine which makes it alkaline and promotes the formation
Uric Acid Stones:
is produced when the body metabolizes protein. When the pH of
urine drops below 5.5, urine becomes saturated with uric acid
crystals, a condition known as hyperuricosuria
When there is too much uric acid in the urine, stones can form.
Uric acid stones are more common in people who consume large
amounts of protein, such as that found in red meat or poultry.
People with gout can also form uric acid stones.
Cystine Stones: Cystine
stones are rare, and they form only in persons with an inherited
metabolic disorder that causes high levels of cystine in the
urine, a condition known as cystinuria.