Kidney Stones - Introduction

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

Introduction

Kidney stones are hard, solid pellets that form in the urinary tract that can cause one of the most painful ailments. In many cases they 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.

In order to understand why this painful condition develops and how it is prevented and treated, it is useful to review the urinary system, which helps to maintain proper water and salt balance throughout the body. The process of urination begins in the kidneys, 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 tiny filtration 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.
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 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 another tube called the urethra.

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

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

Types of Kidney Stones

Occasionally crystals form in urine from various salts that build up on the inner surfaces of the kidney. Eventually these crystals become large enough to form stones in the kidney, a condition called nephrolithiasis. Kidney stones, also referred to as 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.