There are many different kinds of Kidney stones.

Such salts may include calcium oxalate, uric acid, cystine, or xanthine.  These salts can become extremely concentrated under certain circumstances: if the volume of urine is significantly reduced (chronic thirst and dehydration); or if abnormally high amounts of crystal-forming salts are present (infection).  When concentration levels reach the point at which the salts no longer dissolve, they precipitate out and form crystals.

CAUSES OF KIDNEY STONES

Kidney stones develop as a result of a complicated interaction of biologic events that are most likely triggered by genetic susceptibility coupled with dietary factors and lifestyle.

Causes of Calcium Stones

In general, calcium stones form when there are imbalances of components in the urine that either promote or inhibit formation of the stone.

Excess Calcium in the Urine (Hypercalciuria). Hypercalciuria, in which there is too much calcium in the urine, is responsible for about 70% of calcium-combining stones. A number of conditions may produce hypercalciuria. Here are some theories and actual causes:

• Overly efficient intestinal absorption of calcium. In more than half of cases, the source of excess calcium overload in urine is from the intestine, not the kidney. In most cases, a combination of genetic factors conspires to increase calcium absorption. Researchers are investigating a number of suspects, including a possible defective gene that regulates calcitriol, a form of vitamin D, which, in excess levels, may increase intestinal absorption of calcium.
• Excessive chloride. Chloride has a negative charge and calcium a positive one, so they are often used by the body to balance each other. Excess chloride, then, may lead to excess calcium. A gene known as CLCN5, which regulates chloride in the urine, is defective in many patients with calcium stones.
• Renal calcium leak. This is a condition in which the filtering processes in the kidney fail, causing an increase of calcium in the urine.
• Excessive sodium. Calcium absorption in the kidney tubules follows the absorption of sodium and water. High urinary levels of sodium then results in increased levels of calcium. Defects in the kidney tubules transport system can cause imbalances in sodium and phosphate that result in elevated calcium in the urine. A high salt diet can also produce this effect.
• Certain cancers and sarcoidosis (a chronic disorder marked by small lumps on organs) can cause excess calcium.
• Many drugs, including thyroid hormones and loop diuretics (drugs that increase urination), can increase calcium concentration in urine. Stones are an uncommon side effect of these medications, however.

Excess Oxalate in the Urine (Hyperoxaluria). Oxalate, also called oxalic acid, combines with calcium to form calcium oxalate which is the most common stone-forming compound. Excessive oxalate in the urine (hyperoxaluria) is responsible for about 30% of calcium stones and is a more common cause of stones than too much calcium in the urine. A number of conditions can contribute to hyperoxaluria:

• Primary hyperoxaluria (type I or type II). This is an inherited disorder associated with kidney stones.
• Deficiencies of pyridoxine (vitamin B6). Severe vitamin B6 deficiencies (usually due to genetic disorders) can result in overproduction of oxalic acid.
• Short bowel syndrome. Short bowel syndrome is the result of surgery in the small intestine that results in malabsorption. This disorder is the inability of the intestines to absorb fat and nutrients. In such cases, calcium may bind to unabsorbed fat instead of to oxalates. This leaves excess oxalate, which is absorbed by the intestine and excreted into the kidney. People with Crohn's disease, intestinal infections, and children with structural abnormalities in the small intestine are at risk for these procedures and short bowel syndrome.
• Dietary oxalates. Whether eating foods rich in oxalates or taking too much vitamin C plays any major role in hyperoxaluria is unproven. One Swiss study suggests that certain people may be hypersensitive to meat protein, rendering them susceptible to mild hyperoxaluria. [For foods containing oxalates, see How Can Kidney Stones Be Prevented?, below.]
• Hormones. One 1999 animal study suggested that male hormones may account for the greater risk for kidney stones in men. Androgens (male hormones) were associated with a higher risk for calcium oxalate crystals formation while estrogens (female hormones) decreased it. This finding is consistent with others, suggesting that estrogen may protect against the formation of calcium stones by keeping urine alkaline and raising citrate levels. Whether hormone replacement actually prevents stones in older women is not yet determined, however.

Excessive Calcium in the Bloodstream (Hypercalcemia). Hypercalcemia generally occurs when bones break down and release too much calcium into the bloodstream. This is a process called resorption, which can occur because of the following:

• Hyperparathyroidism. Overactive parathyroid glands are the causes of about 5% of calcium stones. And people with this disorder have at least a 20% chance of kidney stones. Women are more likely to have this disorder than men are.
• Immobilization.
• Renal tubular acidosis, disorder that causes acid and alkaline imbalance. It not only increases calcium in the blood stream, it also reduces citrate levels [ see below ].

Low Urine Levels of Citrate (Hypocitraturia) and Other Stone-Inhibiting Compounds. Citrate is the primary agent for removal of excess calcium. Low levels in the urine, known as hypocitraturia, are a significant risk factor for calcium (and also uric acid) stones. Many conditions can reduce citrate levels, but often the causes of hypocitraturia severe enough to cause stones are unknown:

• Renal tubular acidosis. This disorder results in abnormalities in the acid and alkaline balance in the body's fluids, which causes a reduction of citrate in the urine. To make matters worse, the disorder also causes bone resorption and increases calcium levels in the blood.
• Potassium or magnesium deficiency.
• Urinary tract infection.
• Kidney failure.
• Chronic diarrhea.

In addition to citrate, other substances in urine also prevent calcium from precipitating out or forming calcium stones. Some of these include nephrocalcin-A and uropontin (molecules known as glycoproteins), glycosaminoglycan, magnesium, and pyrophosphate.

Nanobacteria Infection. An interesting focus of investigation is the discovery of extremely tiny bacteria, termed nanobacteria, which are able to pass from the blood into urine. Such bacteria coat themselves with mineral deposits that resemble the composition of kidney stones. Cells infected with the bacteria develop mineral deposits both on the inside and outside. Researchers hypothesize that such bacteria may provide the core kidney stones in many people.

Causes of Uric Acid Stones

Excessive Amounts of Uric Acid (Hyperuricuria). Uric acid stones most often form out of high concentrations of uric acid crystals (hyperuricuria). Such crystals are made from purine, a nitrogen end product of dietary protein. They are not related to the acidity of the urine itself, although in the majority of uric acid stones, the urine is so persistently acidic that even normal amounts of uric acid can precipitate and form stones. (About 10% to 20% of cases of uric acid stones are found in urine with normal pH values.) A number of conditions contribute to hyperuricuria:

• Genetic factors.
• Diets overly rich in animal proteins.
• Gout.
• Certain medications (chemotherapy agents, diuretics, and salicylates).
• Binge drinking.
• Fasting.
• Lead toxicity.
• Blood diseases (leukemia, certain uncommon anemias, multiple myeloma, and lymphomas).
• Chronic diarrhea.

Note: Hyperuricuria may also play a role in some calcium oxalate stones. In this case, urate (the salt formed from uric acid) creates a crystal nidus (the nucleus of a crystal), around which calcium oxalate crystals form and grow. Such stones tend to be severe and recurrent.

Causes of Struvite Stones

Struvite stones are almost always caused by urinary tract infections due to bacteria that secrete certain enzymes. These enzymes, in turn, raise urine concentrations of the ammonia that composes the crystals forming struvite stones. The stone-promoting bacteria are usually Proteus, but may also include Pseudomonas, Klebsiella, Providencia, Serratia, and staphylococci. Women are twice as likely to have struvite stones than men are.

Causes of Other Kidney Stones

Other stones, including cystine and xanthine stones, are usually due to genetic abnormalities.

Causes of Cystine Stones. Cystine stones are found in patients with an inherited disorder that causes abnormal transport in the kidney and gastrointestinal system of the amino acids cystine, ornithine, lysine, and arginine.

Causes of Xanthine Stones. In some cases, xanthine stones may develop in patients being treated with allopurinol for gout.

WHAT ARE THE SYMPTOMS OF KIDNEY STONES?

In many cases, kidney stones develop without producing any symptoms. However, if they become lodged in the ureter (the thin tubes between the bladder and the kidney), symptoms can be very severe. Often, they vary depending on the stone's location and then progress.

• Pain usually begins abruptly on one side and then usually continues as intense, constant pain. (In some cases it persists for a few minutes, resolves, and then returns after about 10 minutes.)
• The patient cannot become comfortable and usually stands, sits, paces, or reclines in a vain search for a position that will bring relief.
• If the stone is in the kidney or upper urinary tract, the pain usually occurs in one flank area (to the side of the back near the waist).
• If the stone moves down, the pain may move to the groin.
• If the stone is too large to pass easily, the pain follows the muscle contractions in the wall of the ureter as they try to squeeze the stone along into the bladder.
• Nausea and vomiting may occur.
• Bleeding may occur if the stone becomes larger or moves.
• As the stone passes down the ureter closer to the bladder, a person may feel the need to urinate more often or a burning sensation during urination.
• If fever and chills accompany any of these symptoms, an infection may be present.

It should be noted that the size of the stone does not necessarily predict to the severity of the pain; a very tiny crystal with sharp edges can cause intense pain while a larger round stone may not be as distressing.

HOW SERIOUS ARE KIDNEY STONES?

Pain:  Between 70% and 90% of crystals remain tiny enough so that they can travel through the urinary tract and pass out of the body in the urine without being noticed. When they cause symptoms, however, kidney stones have been described as one of the most painful disorders to afflict humans.

Many people develop kidney stones, without ever knowing it happened to them. Stones can be formed painlessly, and can be dissolved painlessly without that you know you have ever had them.

Why pain?

Cause stones can be very sharp! Stones can cut tissues and cause bleeding.

Risk for Recurrence

Calcium stones recur in 10% of patients within a year of the first attack, in 33% within five years, and in 50% by 10 years. Individual risk for recurrence, however, varies. For example, a 15-year old patient with inherited cystine stones has much higher than average odds for recurrence, while a middle-aged old man with a first calcium oxalate stone has a good chance of never passing another.

Effects on the Urinary Tract and Kidney

Obstruction and Infection. Although obstruction of the urinary tract often occurs, it is usually temporary and causes no lasting damage. In some cases, however, particularly if the obstruction progresses silently, infection may occur, which can be serious and which warrants prompt attention.

Kidney Failure. It is very rare for kidney stones to cause kidney failure. But, the risk factors for kidney failure and risk factors for kidney stones are identical: dehydration!!!!!!!!

Some factors produce a higher risk. They include the following:

• Very frequent recurrences (such as in people with inherited kidney stone disorders).
• Accompanying episodes of urinary tract infections with obstruction (such as from abnormal urinary tracts or spinal cord injuries).
• A history of multiple urologic procedures for kidney stones.
• Size of the kidney stone gravel.

The Kidneys and Urinary Tract Anatomy and Physiology

The urinary system helps to maintain proper water and salt balance throughout the body. The process of urination begins in the kidneys. Kidneys act as blood filter,  which process fluids and dissolved waste matter to produce urine. The two kidneys are located deep behind the abdomen below the ribs and toward the middle-back. They play a major role in this process:

• Each kidney contains over a million nephrons. These are the functional units of the kidney.
• Each nephron is composed of a tiny tuft of blood vessels (a glomerulus) enclosed in a funnel-like structure called a Bowman's capsule s.
• Each glomerulus filters waste products, water, and salts out of the blood fluid (plasma) that has entered the kidney as it circulates through the body.
• About 1% of the plasma is converted into urine. The rest is returned into circulation to prevent dehydration. Urine's primary components are acids and urea and creatine (nitrogen compounds).
• Urine passes from the Bowman's capsule into tiny tubules that lead to large collecting tubes to the center of the kidney. As it passes through this network it becomes increasingly concentrated.
• Urine then flows from kidney through thin tubes called ureters into the bladder.
• The bladder's elastic walls expand to store the incoming urine until it is eliminated from the body via another tube called the urethra.