Kidney Stones Explained

In this TED-Ed video, Dr. Arash Shadman explains what kidney stones are and what causes them.

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Video Transcript

The biggest kidney stone on record weighed more than a kilogram and was 17 centimeters in diameter. The patient didn't actually swallow a stone the size of a coconut. Kidney stones form inside the body, but unfortunately, they're extremely painful to get out.

A kidney stone is a hard mass of crystals that can form in the kidneys, ureters, bladder, or urethra. Urine contains compounds that consist of calcium, sodium, potassium, oxalate, uric acid, and phosphate. If the levels of these particles get too high, or if urine becomes too acidic or basic, the particles can clump together and crystallize.

Unless the problem is addressed, the crystals will gradually grow over a few weeks, months, or even years, forming a detectable stone. Calcium oxalate is the most common type of crystal to form this way, and accounts for about 80% of kidney stones. Less common kidney stones are made of calcium phosphate, or uric acid. A slightly different type of stone made of the minerals magnesium ammonium phosphate, or struvite, can be caused by bacterial infection. And even rarer stones can result from genetic disorders or certain medications.

A kidney stone can go undetected until it starts to move. When a stone travels through the kidney and into the ureter, its sharp edges scratch the walls of the urinary tract. Nerve endings embedded in this tissue transmit excruciating pain signals through the nervous system. And the scratches can send blood flowing into the urine. This can be accompanied by symptoms of nausea, vomiting, and a burning sensation while urinating.

If a stone gets big enough to actually block the flow of urine, it can create an infection, or backflow, and damage the kidneys themselves. But most kidney stones don't become this serious, or even require invasive treatment. Masses less than five millimeters in diameter will usually pass out of the body on their own. A doctor will often simply recommend drinking large amounts of water to help speed the process along, and maybe taking some pain killers.

If the stone is slightly larger, medications like alpha blockers can help by relaxing the muscles in the ureter and making it easier for the stone to get through. Another medication called potassium citrate can help dissolve the stones by creating a less acidic urine.

For medium-sized stones up to about ten millimeters, one option is pulverizing them with soundwaves. Extracorporeal shock wave lithotripsy uses high-intensity pulses of focused ultrasonic energy aimed directly at the stone. The pulses create vibrations inside the stone itself and small bubbles jostle it. These combined forces crush the stone into smaller pieces that can pass out of the body more easily.

But zapping a stone with sound doesn't work as well if it's simply too big. So sometimes, more invasive treatments are necessary. A rigid tube called a stent can be placed in the ureter to expand it. Optical fibers can deliver laser pulses to break up the stone. Stones can also be surgically removed through an incision in the patient's back or groin.

What about just avoiding kidney stones in the first place? For people prone to them, their doctor may recommend drinking plenty of water, which dilutes the calcium oxalate and other compounds that eventually build up into painful stones. Foods like potato chips, spinach, rhubarb, and beets are high in oxalate, so doctors might advise limiting them.

Even though calcium is often found in stones, calcium in foods and beverages can actually help by binding to oxalate in the digestive tract before it can be absorbed and reach the kidneys.

If you do end up with a kidney stone, you're not alone. Data suggests that rates are rising, but that world record probably won't be broken any time soon.

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‍About the Writer

Dr. Arash Shadman is a neurologist in Temple, Texas and is affiliated with Baylor Scott and White Medical Center-Temple. He received his medical degree from Shiraz University of Medical Sciences and has been in practice for more than 20 years.

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Patient Education Disclaimer

This material is for informational purposes only. It does not replace the advice or counsel of a doctor or health care professional. KidneyLuv makes every effort to provide information that is accurate and timely, but makes no guarantee in this regard. You should consult with, and rely only on the advice of, your physician or health care professional.

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