Renal pelvis

At a glance

English

Renal pelvis

Latin (TA2)

Pelvis renalis

System

Urinary

Region

Abdomen

Side

Paired, left and right

About the renal pelvis

Each kidney drains its urine into a branching set of channels inside the renal sinus, the hollow behind the hilum. Small cup-shaped minor calyces fit over the renal papillae and receive urine from them. They join into a few (usually two or three) major calyces, which in turn merge into a single wide chamber, the renal pelvis. The pelvis narrows as it leaves the hilum and continues downwards as the ureter, so it can be thought of as the expanded top of that tube.

Its shape varies. In many people the pelvis lies largely within the sinus, surrounded by fat, branches of the renal vessels and nerves; in others most of it sits outside the hilum, an extrarenal pelvis. At the hilum it is the most posterior of the main structures: the renal vein lies in front, the renal artery between, and the pelvis behind. The point where it tapers into the ureter, the pelviureteric junction, is one of the natural narrow points of the urinary tract.

The wall resembles that of the ureter. A lining of transitional epithelium, the urothelium, rests on a lamina propria of connective tissue and is surrounded by smooth muscle. Pacemaker cells near the calyces start waves of contraction that sweep urine out of the calyces, through the pelvis and on down the ureter by peristalsis, rather than letting it drain by gravity alone.

The pelvis is a frequent site of disease. Infection that climbs up the ureter and inflames the pelvis and kidney tissue is pyelonephritis, with loin pain and fever. Stones can form here, and a large branching staghorn calculus may fill the pelvis and calyces. Narrowing at the pelviureteric junction causes the pelvis to swell with retained urine, hydronephrosis, which is graded partly by the width of the pelvis on ultrasound. Urothelial cancers can also arise in its lining. The prefix pyelo- refers to the renal pelvis, as in pyelogram.

Function and supply

Begins at

Formed in the renal sinus where the major calyces unite.

Ends at

Narrows at the pelviureteric junction, near the hilum, to become the abdominal part of the ureter.

Function

Receives urine from the calyces and drives it into the ureter by peristaltic contraction of its smooth muscle.

Nerve supply

Autonomic fibres from the renal plexus; pain from distension travels with sympathetic fibres to the lower thoracic and upper lumbar segments, felt in the loin.

Blood supply

Branches of the renal artery; venous blood drains to the renal vein.