How is urine propelled down the ureter to the bladder?

Urine is propelled down the ureter to the bladder primarily through a process known as peristalsis. Peristalsis involves rhythmic contractions of the smooth muscle in the walls of the ureters, which generates a wave-like motion. This motion effectively pushes the urine from the renal pelvis, through the ureters, and into the bladder.

The structure of the ureters, being muscular tubes, is specifically adapted for this rhythmic contraction, ensuring that urine moves in one direction—towards the bladder. This mechanism is crucial for the proper functioning of the urinary system, as it helps prevent the backflow of urine, which could lead to complications such as urinary tract infections or kidney damage.

In contrast, while gravity may assist in the flow of urine when a person is in a vertical position, it is not the primary force responsible for the movement of urine through the ureters. Compression does occur during the contraction of the ureteral muscles, but it is not a standalone process for urine propulsion. Surge waves are not a recognized term in this context, making peristalsis the clear correct choice for how urine travels through the ureters.