Renal Colic (Urolithiasis)
Sudden ureteric obstruction by a stone that raises pressure upstream and triggers smooth muscle spasm, producing pain whose exact location tracks the stone's position as it migrates towards the bladder.
First principles
Stones form when the urine is supersaturated, and colic begins when one obstructs
Urine is normally undersaturated with the salts (chiefly calcium oxalate, calcium phosphate, uric acid or, less commonly, struvite or cystine) that make up stones, but when concentration rises (from dehydration, metabolic excess, urinary stasis or infection), crystals nucleate and grow into stones within the collecting system. A stone itself is often silent while it sits in the renal pelvis. Renal colic begins the moment a stone enters and obstructs the narrow ureter, converting a static structural problem into an acute obstructive emergency.
Educational content pending clinical review. Not medical advice.