The renal pelvis refers to the funneling area of the kidney responsible for urine collection. It is the portion of the kidney where either two or three major calyces join. Major calyces are structures that are part of an extensive drainage system within each kidney. Even though the renal pelvis is where the flow of urine begins, urine has already gone through the processes of filtration and reabsorption before it reaches this area. Although rare, tumors of the renal pelvis are a rare neoplasmic condition of the upper portion of the urinary tract.
Encompassing the kidneys, urinary bladder, and their ducts, the human urinary system is generally contained within the ventral abdominopelvic cavity. Located under the diaphragm in the mid-back region lie the kidneys, which resemble two red beans. Each kidney is associated with a pair of ureters and these lead directly into the bladder, as the urethra leads from the bladder to an external opening on the outside of the body. Evidenced by women’s susceptibility to urinary infection, the urethra is longer in males and considerably shorter in females.
By the time that concentrated urine reaches the renal pelvis, its condition has been significantly changed. Useful substances have been returned to the blood by reabsorption, while wastes and excess materials that entered by filtration or secretion have been retained. Concentrated urine is mostly composed of water; the rest is nitrogenous waste and salts.
Urinary flow starts from within the renal pelvis of the kidney, into the ureters, into the bladder, and out of the body via the urethra. As urine is produced, it moves from the collecting area, ducts called the renal papilla, and into the renal pelvis. Urine flows into the paired ureters and on into the urinary bladder where it is further collected. Capable of holding up to 2 cups (473 ml) of urine at one time, the bladder then shrivels down to the size of a mid-sized nut after it has been emptied.
In rare instances, people develop tumors inside of the renal pelvis of the kidney. Characterized by pain and blood in the urine, urothelial masses may alter urinary system structure and obstruct the normal flow or urine. Smoking and high caffeine intake has been linked to cancer of the upper urinary tract, particularly in men. Typical treatment of the disease depends on tumor staging, although surgery and chemotherapy are usually the standard therapy for masses upwards of stage two.