Urolithiasis

Case Presentation

Daniel, a thirty-two year old history instructor, was in his office preparing notes for an upcoming seminar presentation when he was struck with a very sudden and intense pain in his side and lower back. He remained at his desk, breathing deeply, and the pain began to recede. Five minutes later, the pain was not as severe but Daniel was still uncomfortable and decided to call his physician. Daniel described his symptoms to the doctor's receptionist and made an early afternoon appointment. One of Daniel's colleagues drove Daniel to the doctor's office. While on the way to his appointment, Daniel experienced another bout of severe pain and began to feel nauseous. The pain seemed to be spreading into his lower abdomen and groin.

After asking Daniel a few questions about his symptoms, the doctor requested an abdominal x-ray, several blood tests, and urinalysis. As Daniel supplied the urine sample he was disturbed to notice that the urine had a pinkish cast. The physician returned and informed Daniel that he had a kidney stone which, based on its size, should pass on its own within a day or so. The doctor told Daniel that he should rest at home until the stone passed, drink at least 2-3 quarts of water each day, and strain his urine in order to retrieve the stone for analysis. The doctor also gave Daniel a prescription for pain medication.

Daniel passed the stone the following morning and brought it to the doctor's office. Analysis of the stone's composition revealed that it was a calcium stone. Daniel's blood and urine tests had also shown high calcium levels. Based on this, the doctor told Daniel to eat fewer foods containing calcium or oxalate and provided Daniel with a list of foods to limit. He also told Daniel to continue to drink at least two quarts of water each day.

Case Description

The presence of kidney stones, or urinary caliculi, in the urinary tract is called urolithiasis. These stones form from materials that are excreted by the kidneys. Normally these excreted materials stay dissolved in urine, but in some individuals they form precipitates that can develop into kidney stones. Kidney stones can form from several different substances. Kidney stone analysis, blood tests, and urinalysis all assist a physician in determining how best to avoid the development of future stones. Calcium stones are most common, comprising between 80 and 90 percent of urinary caliculi. The calcium stones are formed from calcium phosphate or calcium oxalate, and persons predisposed to developing these stones are often instructed to decrease calcium and oxalate intake. In some cases, medications are prescribed that decrease calcium excretion by the kidneys or alter urine pH, a factor in kidney stone formation.

The pain associated with the blockage of the urinary tract by a kidney stone is called renal colic and can be very intense. Treatment depends primarily on the size of the stone. Stones smaller than 5 mm are usually passed without assistance, and passage is facilitated by drinking plenty of water. Larger stones can be pulverized with shockwaves or surgically removed depending on the size and the location of the stone. Sometimes, a stone within a ureter is removed by inserting a fiberoptic device through the urethra and ureter and either grabbing or destroying the stone.

1			List the components of the urinary tract from the renal pelvis outward.
2			Why would water facilitate the passage of kidney stones?
3			Why would water aid in the prevention of developing future kidney stones?
4			List the three stages in the formation of urine and describe each stage with regard to the structures involved and the direction substance transport.
5			The glomerular filtrate concentration of calcium (Ca+2) is about 4 mEq/L. The concentration of calcium in the urine is about 5 mEq/L. How would you explain this difference?