Urine and Ions
As the National Institute of Diabetes and Digestive and Kidney Disorders (NIDDK) explains, one of the main jobs that the kidneys have is to filter out excess water and waste products from the blood via the creation of urine. These waste products are dissolved in the water-based environment of the kidneys. However, as is true for any dissolved substance, there is only so much that can be dissolved in the urine. This is especially true for the kidneys where there are a number of dissolved minerals and electrolytes that can combine together to form solids, which are called kidney stones.
Formation
Kidney stones form when the concentration of certain minerals and other compounds get too high in the urine, which causes them to no longer be dissolved and to form small bits of solid. As the Mayo Clinic notes, many kidney stones are caused by too much calcium building up in the urine. Calcium can combine with another dissolved mineral, called calcium oxalate, to form kidney stones. Kidney stones can also be caused by abnormally high levels of a chemical called struvite, which is formed when the urinary tract becomes infected. Kidney stones can also be made out of uric acid, which can build up to unusually high levels when a person becomes dehydrated. Once a kidney stone has started its formation, it forms a seed, and other minerals can come out of solution more easily and cause the stone to grow.
Symptom Development
Kidney stones cause pain when they get caught in parts of the urinary tract. Typically, kidney stones get trapped in the ureter, which is the tube that connects the kidneys to the bladder. The kidney stone can cause pain because urine is no longer able to flow through these structures, and also because they can cause damage and irritation to the ureter, causing inflammation. Sometimes kidney stones also get caught in the bladder or in the urethra, which is where the bladder expels urine from the body. Again, kidney stones here can cause obstruction and pain. Kidney stones typically will dissolve away on their own, but sometimes special medications are needed to speed the process. Otherwise, kidney stones can be surgically removed or broken into small pieces using ultrasound.
