A calyx refers to those portions of a kidney that are the start of the urinary collection process taking place after filtration. The majority of kidneys contain between six and 10 calyces. There are two types: minor calyces and major calyces.
A minor calyx drains one renal papilla, which empties into a single minor calyx through a projection into its lumen. The renal papillae represent the tips of renal pyramids and the location where urine leaves the filtering portion of the kidney tissue to enter the collecting area. Two or three minor calyces combine to form a major calyx and a major calyx drains from several renal papillae. All of the major calyces combine to create the area in the kidney, known as the renal pelvis, the large collecting duct for urine that is surrounded by the renal sinus. Peristalsis, originating in the smooth muscle of the calyces and initiated by pacemaker cells, enables urine to be propelled through both the renal pelvis and the ureters to the bladder.
The kidneys are the main excretory organs of the urinary tract and are found on the posterior abdominal wall. Their superior sections can reach up to the 12th or 11th rib. Urologists treating patients for kidney stones usually check the calyces for overlooked stones during ureteroscopy.