Renal calyces are parts of the kidney that collect urine before it passes further into the urinary tract. The calyces are part of the renal pelvis, a convex system of sinuses that connect the innermost part of the kidney to the ureters and, from there, to the bladder. There are two types of renal calyx: the minor calyx and the major calyx. In the human body, there can be two to three major calyces and eight to fourteen minor calyces. Basically, the renal calyces are sectional, hollow cavities that act as reservoirs and help the kidneys perform their duty.
The function of the kidney is to filter out waste and excess water from about 200 quarts of blood every day. Most of this processing takes place in the renal cortex and the renal medulla, the "meaty" parts of the kidney. Once this filtration process is complete, the waste is expunged into the renal calyces and collected. The calyces, branching vessels connected to the kidney interior, empty into the renal pelvis, forming the initial portion of the lower urinary tract.
The different lobes of the kidney each have a medullary pyramid that is capped by a renal papilla. Renal papilla function as strainers; as urine is processed through the renal cortex and then the renal medulla, drops of urine are sent through the papilla to collect in the cavities of the renal calyces. Initially, this will be through the minor calyces, but every minor calyx joins to a major calyx, and the major calyxes then funnel all collected urine into the renal pelvis and, from there, the ureter and finally the bladder.
Cancer of the upper urinary tract is rare, but three-fourths of all such cases form tumors in the renal calyces or the renal pelvis. The susceptibility of these parts of the kidney to malignant cell growth stems from a tissue layer called the urothelium. This tissue is found in the bladder and the upper urinary tract and helps prevent previously filtered wastes from getting back into the bloodstream. Due to constant bombardment by toxins filtered from the blood, the areas where urine waste is the most present, such as the renal pelvis and calcyes, are also vulnerable to tumor growth. In fact, cancer of the urothelium ranks fifth in the U.S. among all cancers if skin cancer is excluded, and the renal calyces and pelvis account for about three-fourths of all cancer occurring in the urothelium.