Kidney stones are one of the most common
disorders of the urinary tract. Kidney stones or renal stones are
gravel-like collections of chemicals that may appear in any area of the
urinary system, from the kidney to the bladder. They may be small or
large, single or multiple. One in every 20 people develops a kidney
stone at some point in their life.
The condition of having kidney stones is termed nephrolithiasis. Having
stones at any location in the urinary tract is referred to as
urolithiasis.
Types of stones-
Calcium oxalate stones
The most common type of kidney stone is composed of calcium oxalate
crystals, occurring in about 80% of cases,[2] and the factors that
promote the precipitation of crystals in the urine are associated with
the development of these stones.
Common cause is increased consumption of calcium in diet. However,
current evidence suggests that the consumption of low-calcium diets is
actually associated with a higher overall risk for the development of
kidney stones. This is perhaps related to the role of calcium in
binding ingested oxalate in the gastrointestinal tract. As the amount
of calcium intake decreases, the amount of oxalate available for
absorption into the bloodstream increases; this oxalate is then
excreted in greater amounts into the urine by the kidneys. In the
urine, oxalate is a very strong promoter of calcium oxalate
precipitation, about 15 times stronger than calcium.
Uric acid (urate)
Multiple kidney stones composed of uric acid and a small amount of
calcium oxalate.
About 5-10% of all stones are formed from uric acid. This might be
occurring when fluid intake is less. They may occur when uric acid
excretion is increased in urine. This is often found with gout and
chemotherapy.
Other types
Other types of kidney stones are composed of struvite (magnesium,
ammonium and phosphate); calcium phosphate; and cystine.
The formation of struvite stones is associated with the presence of
urea-splitting bacteria, most commonly Proteus mirabilis (but also
Klebsiella, Serratia, Providencia species). These organisms are capable
of splitting urea into ammonia, decreasing the acidity of the urine and
resulting in favorable conditions for the formation of struvite stones.
Struvite stones are always associated with urinary tract infections.
Cause-
Kidney stones form when there is a decrease in urine volume and/or an
excess of stone-forming substances in the urine.
Dehydration from reduced fluid intake or strenuous exercise without
adequate fluid replacement increases the risk of kidney stones.
Obstruction to the flow of urine can also lead to stone formation.
Kidney stones can also result from infection in the urinary tract.
A number of different medical conditions can lead to an increased risk
for developing kidney stones:
1. Gout results in an increased amount of uric acid in the urine and
can lead to the formation of uric acid stones.
2. Hypercalciuria (high calcium in the urine), another inherited
condition, causes stones in more than half of cases. In this condition,
too much calcium is absorbed from food and excreted into the urine,
where it may form calcium phosphate or calcium oxalate stones.
3. Other conditions associated with an increased risk of kidney stones
include hyperparathyroidism, kidney diseases such as renal tubular
acidosis, and some inherited metabolic conditions including cystinuria
and hyperoxaluria. Chronic diseases such as diabetes and high blood
pressure (hypertension) are also associated with an increased risk of
developing kidney stones.
4. People with inflammatory bowel disease or who have had an intestinal
bypass or ostomy surgery are also more likely to develop kidney stones.
5. Some medications also raise the risk of kidney stones. These
medications include some diuretics, calcium-containing antacids, and
the protease inhibitor indinavir (Crixivan), a drug used to treat HIV
infection.
Predisposing factor-
Environmental and dietary factors-
Low urine volumes.
High ambient temperatures.
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