The renal pelvis is a central structure within the kidney, performing a specialized role in the urinary system. It acts as a collection point for urine, gathering it from the kidney’s filtering units. This funnel-shaped chamber is a component of the larger urinary tract, which is responsible for filtering waste products from the blood and expelling them from the body. The renal pelvis serves as a conduit, directing urine out of the kidney towards the bladder.
Anatomy and Location
The renal pelvis is located deep within the kidney, specifically nestled within a cavity called the renal sinus. This sinus is a fat-filled space found at the kidney’s medial indentation, known as the renal hilum. The hilum serves as the entry and exit point for various structures, including blood vessels, nerves, and the ureter. The renal pelvis itself represents the expanded, upper end of the ureter, which is the tube that carries urine from the kidney to the bladder.
The renal pelvis has a distinctive funnel shape, allowing it to efficiently collect urine. It receives urine from cup-like extensions within the kidney called calyces. Minor calyces surround the tip of each renal pyramid where urine is released, and major calyces form from the convergence of several minor calyces. Typically, two or three major calyces unite to form the renal pelvis.
The walls of the renal pelvis contain smooth muscle fibers and are lined with a specialized type of tissue called transitional epithelium, also known as urothelium. This lining prevents urine absorption and allows the structure to stretch as it fills.
Role in Urine Transport
The primary function of the renal pelvis involves the collection and directed transport of urine. As urine is produced by the kidney’s filtering units, it drains into the minor calyces, then into the major calyces, and finally collects within the renal pelvis.
Once urine accumulates, the muscular walls of the renal pelvis move it along. Smooth muscle fibers contract in rhythmic waves, a process known as peristalsis. These contractions propel urine from the renal pelvis into the ureter, preventing stagnation within the kidney. The renal pelvis contains specialized “pacemaker” cells that initiate these contractions, ensuring a continuous flow of urine towards the bladder. This mechanism is important for maintaining the one-way flow of urine and preventing backflow into the kidneys.