In exothermic reactions, the products have higher energy than the reactants, and in endothermic reactions, the reactants have higher energy than the products.
In addition to gravity, muscular peristaltic waves, originating in the renal pelvis, squeeze urine down the ureters and squirt it into the bladder, the peristaltic movements consist of radially symmetrical contractions and in the relaxation of the muscles that propagate in a wave downwards in the muscular tube, in an antegrade manner, such movements are also found in the esophagus and stomach.
It is like a animal migrating because it is like hibernating because it doesn't get any food or water in winter.
I'm pretty sure tension is your answer.
