<prompt> The narrowest pa of the ureter is at:Uretero-pelvic junctionIliac vessel crossingPelvic ureterUreterovesicle junction  <response>: The narrowest lumen is where the ureter enters the bladder wall ureterovesicle junction and may be responsible for arresting the passage of stones of as little as 2-3 mm. Note: Sometime the question may not have the option of ureterovesical junction, in that case the intramural ureter the pa inside detrusor may be taken as the answer. 