Our kidneys are bean-shaped organs, each about the size of our fists. They are located near the middle of our back, just below the rib cage. The kidneys are sophisticated trash collectors. Every day, our kidneys process about 200 quarts of blood to flush out about 2 quarts (fourth part of gallon, two pints) of waste products and extra water which together become urine that flows to our bladder through tubes called ureters. Our bladder stores urine until we feel urge to go to the bathroom.
The wastes in our blood come from the normal breakdown of active muscle and from the food we eat. Our bodies use the food for energy and self-repair. After our bodies have taken what they need from the food, waste is sent to the blood. If our kidneys do not remove these wastes, the wastes would build up in the blood and damage our bodies. In addition to removing wastes, our kidneys help control blood pressure. They also help to make red blood cells and keep our bones strong.
Many ions circulate in our bloodstream, some combinations of which can precipitate to form kidney stones. Kidney stones, or renal calculi, are solid concretions (crystal aggregations) of dissolved minerals in urine; calculi typically form inside the kidneys or ureters. The terms nephrolithiasis and urolithiasis refer to the presence of calculi in the kidneys and urinary tract, respectively. There are four major types of kidney stones:
1. The most common type of stone contains calcium that is a normal part of a rich diet. Calcium that is not used by the bones and muscles goes to the kidneys. In most people, the kidneys flush out the extra calcium with the rest of the urine but in some people it is accumulated in their kidneys. The calcium ions that stay behind in kidneys join anionic waste products such as oxalate and phosphate ions to form a stone.
2. A struvite stone may form after an infection in the urinary system. These stones contain the mineral magnesium and the waste product ammonia.
3. A uric acid stone may form when there is too much acid in the urine. Those of us, who have acquired tendency to form uric acid stones, should vow to cut back on the amount of meat they eat.
4. Cystine that is a sulfur-containing amino acid produced by digestion or acid hydrolysis of proteins, and sometimes found in the urine and kidneys, and readily reduced to two molecules of cysteine, can build up in the urine to form a stone. Though cystine stones are rare, the disease that causes cystine stones runs in families.
Kidney stones may be as small as a grain of sand or as large as a pearl. Some stones are even as big as golf balls. Stones may be smooth or jagged. They are usually yellow or brown. A stone may stay in the kidney or break loose and travel down the urinary tract. A small stone may pass out of the body without causing much discomfort. A larger stone may get stuck in a ureter, the bladder, or the urethra. Problems arise when stones block the flow of urine and cause great pain. Some stones can become large enough to be extremely painful and even life-threatening, requiring treatment by drugs, lasers, or surgical removal.
It has been discovered that kidney stones generally consist of insoluble calcium and magnesium compounds such as calcium oxalate, calcium phosphate, magnesium ammonium phosphate, or a mixture of these. For calcium oxalate kidney stones, the following equilibrium applies:
CaC2O4(s) Ca2+ (aq) +C2O42-(aq)
High intake of foods rich in calcium or oxalate can cause a rise in the urinary concentration of either ion or both, sufficient to shift the equilibrium to the left and cause the ionic product to become greater than the solubility product that is the product of concentrations of ions in a saturated solution of a highly soluble salt, each raised to the power of the coefficient in a balanced equation. The result is precipitation of calcium oxalate as a kidney stone. Thus, foods rich in calcium, such as milk, ice cream, and cheese etc., or high in oxalate ions, such as chocolate, spinach, and black tea, and likes, can trigger the onset of a kidney stone through the common ion effect (A common ion is an ion that is produced by more than one solute and the shift in an existing ionic equilibrium caused by the addition of common ions is called the common ion effect). Such foods are restricted in the diets of individuals prone to developing kidney stones. A high sugar diet may also create kidney stones because excessive sugar promotes excretion of calcium and magnesium ions, which increase the concentration of these ions while passing through the kidneys.
In order to avoid both the onset of kidney stone and formation of more stones one should drink more water. In fact we should try to drink 12 full glasses of water a day as drinking lots of water helps us flush out the substances that form stones in the kidneys. We can also drink ginger ale, lemon-lime sodas, and fruit juices. But water is the best. We should limit our coffee, tea, and cola to one or two cups a day because the caffeine may cause us lose fluid too quickly. Generally doctors ask patients to eat more of some foods and to cut back on other foods. For example, if one has a uric acid stone, the doctor may ask him/her to eat less meat, because meat breaks down to make uric acid. Besides, a doctor may give the patient some medicines to prevent formation/aggravation of calcium and uric acid stones.