What does the renal pelvis do in the urinary system?

The renal pelvis serves as the funnel for urine flowing from the kidneys to the ureters, playing a critical role in the urinary system. Specifically, it collects urine produced by the nephrons in the kidneys and holds it temporarily before it is transported to the bladder via the ureters. This function is essential as it allows the kidneys to deliver the urine efficiently while also ensuring that the bladder can fill to a certain level before triggering the sensation of needing to urinate.

The other choices pertain to functions not related to the renal pelvis. For example, filtering blood is primarily conducted by the nephrons within the kidneys, while blood pressure regulation involves various systems including hormonal pathways and the kidneys' overall function but is not a direct role of the renal pelvis. Similarly, hormone production is mainly associated with the kidneys themselves or other glands in the body, rather than the renal pelvis specifically. Thus, the choice that states the renal pelvis holds urine before it enters the bladder accurately describes its specific function within the urinary system.