Why does the pain of passing kidney stones tend to come in waves?
The peristaltic contractions of the ureter cause pain when those contractions squeeze down on a kidney stone. The contractions are intermittent, so the pain lets up when the ureters are not contracting.
The ureter is a muscular tube that pushes urine toward the bladder by contracting.
The contractions are triggered by pacemaker cells near
the top of the ureter.
These contractions travel in peristaltic waves down the ureter to the bladder, pushing urine along.
The contractions are strong enough to close or nearly close the lumen of the ureter.
If a kidney stone is present, the patient experiences pain when these strong contractions close and grip on the stone, until the peristaltic wave finally moves on down the ureter.
Like many other peristaltic tubes, the ureters are not particularly sensitive to the pain of puncture, but are highly sensitive to the pain of inflation. That is why gas trapped in the intestine can be so painful.
The pressure of the peristaltic wave of the ureter squeezing down on a kidney stone when it's trying to contract is painful.
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