Urodynamic Events: Rebound of the Papilla
The previous figure neglected to describe what occurs during rebound, that is, when the papilla, following the peristaltic contraction, retracts and becomes shorter and broader. This is important, because fluid leaves the collecting duct cells at that time.  This shows the rebound more clearly. One can see the blue tip of the papilla moving upwards. When the action is stopped, it can be seen that the papilla is pale, without blood, during rebound, and becomes pink from the returning blood when the papilla relaxes.

Rebound