The tip of the pyramid ends in a cuplike structure called the papilla.
Papilla projects into a calyx. Its surface has a sievelike appearance since it is where urine droplets pass through its small openings. Each opening represents a tubule known as the Bellini duct through which collecting tubules within the pyramid converge or meet. The muscle fibers lead from the calyx to the papilla. As the muscle fibers originating from calyx contract, urine flows through the Bellini ducts into the calyx. The urine flows through the renal pelvis and the ureter and it eventually drains down into the bladder.
