The renal pelvis is a funnel-shaped structure in the kidney that plays a critical role in collecting and transporting urine from the kidney to the ureter.[4] As a central component of the urinary system, the renal pelvis ensures the efficient flow of urine from the filtration structures within the kidney to the bladder for excretion.[1]
Anatomy of the Renal Pelvis
The renal pelvis is located within the hilum of the kidney, the area where blood vessels, nerves, and the ureter enter or exit. It acts as the initial section of the ureter, connecting the kidney’s internal collecting system to the rest of the urinary tract.[2]
Key anatomical components:
- Minor Calyces: Small cup-shaped structures that collect urine from the renal pyramids’ papillae. Each kidney contains 8 to 18 minor calyces.
- Major Calyces: Larger collecting chambers formed by the convergence of minor calyces. Each kidney typically has 2 to 3 major calyces.[8]
- Central Funnel: The major calyces merge to form the renal pelvis, which narrows into the ureter.
Structure
- Lining Epithelium: The renal pelvis is lined by transitional epithelium, also known as urothelium. This specialized tissue can stretch to accommodate varying volumes of urine.
- Muscular Wall: The renal pelvis has a smooth muscle layer that facilitates the propulsion of urine through peristaltic contractions.[3]
- Supportive Tissue: Surrounding the renal pelvis is connective tissue, which provides structural support and protection.
Function
The primary function of the renal pelvis is to act as a conduit for urine transport:
- Urine Collection: It gathers urine from the major calyces, which, in turn, receive urine from the minor calyces connected to the renal pyramids.[7]
- Urine Transport: The smooth muscle in its walls generates peristaltic waves to propel urine into the ureter, ensuring uninterrupted flow to the bladder.[6]
- Reservoir Role: Temporarily stores small amounts of urine before transferring it to the ureter.
Clinical Relevance
- Hydronephrosis: Blockage or obstruction in the ureter or renal pelvis can cause urine to accumulate, leading to swelling and dilation of the renal pelvis, a condition known as hydronephrosis.
- Kidney Stones: The renal pelvis is a common site for the formation and lodgment of kidney stones, which can obstruct urine flow and cause severe pain.
- Pyelonephritis: Infections affecting the renal pelvis and kidney tissue can result in inflammation, leading to a condition called pyelonephritis.
- Renal Pelvis Tumors: Transitional cell carcinoma, a type of cancer, can develop in the renal pelvis, requiring early detection for effective treatment.[5]