Kidney Stones - Introduction

Highlights	Diagnosis	Prevention
Introduction	Treatment	Resources
Causes	Medications	References
Risk Factors	Other Treatments
Symptoms	Complications

Introduction

Kidney stones are hard, solid rocks that form in the urinary tract. They are one of the most painful ailments. In many cases, the stones are very small and can pass out of the body without any problems. But if a stone (even a small one) becomes lodged and blocks the flow of urine, excruciating pain may result, and prompt medical intervention may be needed.

The process of urination begins in the kidneys. The kidneys process fluids and dissolve waste matter to produce urine. The two kidneys are located deep behind the abdomen below the ribs and toward the middle of the back.

Each kidney contains over a million nephrons. These are the tiny filtration units of the kidney.
Each nephron is composed of a tiny group of blood vessels (a glomerulus) enclosed in a funnel-like structure called a Bowman's capsule.
Each glomerulus filters waste products, water, and salts out of the blood fluid (plasma) that has entered the kidney.
About 1% of the blood fluid is converted into urine. The rest is returned into circulation to prevent dehydration. Urine's is primarily made of acids, urea, and creatine (nitrogen compounds).
Urine passes from the Bowman's capsule into tiny tubules that lead to large collecting tubes in the center of the kidney. As the urine passes through this network it becomes increasingly concentrated.
Urine then flows from the 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 a tube called the urethra.

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The kidneys are responsible for removing wastes from the body, regulating electrolyte balance and blood pressure, and stimulating red blood cell production.

Click the icon to see an image of the urinary tract.

Types of Kidney Stones

Occasionally, various salts build up on the inner surfaces of the kidney and form crystals. Eventually these crystals become large enough to form stones in the kidney, a condition called nephrolithiasis. Kidney stones (renal calculi) may also form in the ureter or the bladder. The salts that form these stones are made up of combinations of minerals and other chemicals, some of which are derived from a person's diet.