Kidney stones

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Kidney stones



Kidney stones


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USMLE® Step 1 questions

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Kidney stones

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USMLE® Step 1 style questions USMLE

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A 45-year-old woman comes to the outpatient clinic because of intermittent left flank pain that has been ongoing for the past two weeks. She has noticed blood in her urine on a few occasions. Moreover, the pain has become more severe. She works as a personal trainer. Family and medical history are unremarkable. Temperature is 39.0°C (102.2°F), pulse is 80/minute, respiratory rate is 16/minute, and blood pressure is 130/95 mm Hg. An x-ray is ordered and shown below:

Retrieved from:

Which of the following best describes the composition of this pathological structure?

External References

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kidney stones p. 628

Ammonium magnesium phosphate (kidney stones) p. 628


kidney stones and p. 628

Calcium (kidney stones) p. 628

Calcium oxalate nephrolithiasis p. 67

Cystine (kidney stones) p. 628

Gout p. 477

kidney stones and p. 628

Hematuria p. 620

kidney stones p. 626

Hydronephrosis p. 623

kidney stones p. 628


kidney stones and p. 628

Kidney stones p. 626

Crohn disease association p. 391

electrolyte disturbances p. 615

hematuria with p. 618

horseshoe kidney and p. 603

hydronephrosis p. 623

hyperparathyroidism p. 344

postrenal azotemia p. 626

risk factors for p. 617

UTIs p. 179

Klebsiella spp. p. 143

kidney stones p. 628


kidney stones p. 628

Nephrolithiasis p. 624

calcium oxalate p. 67


kidney stones and p. 628

Proteus mirabilis

kidney stones p. 628

Pyelonephritis p. 625

kidney stones p. 628

Staghorn calculi p. 628

Staphylococcus saprophyticus p. , 134

kidney stones p. 628

“Stone bone p. 472

Uric acid (kidney stones) p. 628


Content Reviewers

With nephrolithiasis, “nephro-” refers to the kidneys, and “-lithiasis” means stone, so nephrolithiasis means kidney stones, sometimes also referred to as renal calculi or urolithiasis.

Kidney stones form when solutes in the urine precipitate out and crystalize, and although these most commonly form in the kidneys themselves, they can also form in the ureters, the bladder, or the urethra.

Now, urine’s a combination of water, which acts as a solvent, and all sorts of particles, or solutes.

In general, when certain solutes become too concentrated in the solvent, they become supersaturated.

Urinary supersaturation of certain solutes results in precipitation out of the solution and formation of crystals.

Those crystals then act as a nidus, or place where more solutes can deposit and over time it builds up a crystalline structure.

This can happen if there’s an increase in the solute, or a decrease in the solvent, as would be the case with dehydration.

In addition, there are substances like magnesium and citrate that inhibit crystal growth and aggregation, preventing kidney stones from forming in the first place.

In the majority of cases, the inorganic precipitate is calcium oxalate, formed by a positively charged calcium ion binding to a negatively charged oxalate ion, which results in a black or dark brown colored stone that is radio-opaque on an Xray, meaning that it shows up as a white spot.

Sometimes, instead of oxalate, the calcium binds a negatively charged phosphate group to form calcium phosphate stones which are dirty white in color and also radiopaque on an X-ray.

Calcium oxalate crystals are more likely to form in acidic urine, whereas calcium phosphate crystals are more likely to form in alkaline urine.

The exact reason why these stones form is usually unknown, but there are some known risk factors like hypercalcemia and hypercalciuria, having too much calcium in the blood and urine, respectively.


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  7. "Diagnosis and Management of Acute Ureterolithiasis" American Journal of Roentgenology (2000)
  8. "Kidney stone disease" Journal of Clinical Investigation (2005)
  9. "An Update and Practical Guide to Renal Stone Management" Nephron Clinical Practice (2010)

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