Urine transport: ureter peristalsis and bladder filling
- Mechanism
- For completeness
Waves of muscle squeeze urine down the ureters; the bladder stretches to hold it with little rise in pressure until it is nearly full.
Also called: Cystometrogram, Ureterorenal reflex, Vesicoureteral valve
See it in 3D: Renal pelvis · Ureters · Urinary bladder · Trigone of bladder
What it is
Urine does not fall to the bladder by gravity: smooth-muscle waves started by pacemaker cells in the calyces and pelvis push it down the ureter. The ureter crosses the bladder wall obliquely, which makes a flap valve against reflux. The bladder then fills at low pressure because its wall relaxes as it stretches; pressure rises steeply only near capacity, as shown on the cystometrogram.
How it works, step by step
- Urine from the collecting ducts stretches the calyces and pelvis; pacemaker cells there fire faster.
- A peristaltic wave spreads down the ureter, a few times per minute, carrying a bolus of urine.
- At the bladder, the ureter runs obliquely through the detrusor for 1–2 cm before opening at the trigone.
- Bladder filling and voiding raise intravesical pressure, which flattens the intramural ureter and blocks backflow.
- The bladder wall (smooth muscle, stress relaxation) stretches with little rise in pressure while volume rises to a few hundred mL.
- Near ≈ 300–400 mL, wall tension and pressure climb fast; stretch receptors send stronger signals and micturition waves become frequent.
- A ureteric stone stretches the ureter: pain fibres (T11–L2) give colic that radiates to the groin, and a sympathetic reflex constricts renal arterioles.
Approximate values (adult)
| Parameter | Value | Note |
|---|---|---|
| First desire to void | ≈ 150–250 mL | |
| Usual capacity | ≈ 400–500 mL | |
| Bladder pressure during filling | ≈ 5–15 cmH₂O | stays low until near capacity |
| Intramural ureter length | ≈ 1–2 cm | shorter in reflux |
| Residual volume after voiding | < 50 mL | higher in outlet obstruction or weak detrusor |
Approximate values for a healthy adult at rest; each laboratory sets its own ranges.
Clinical notes
- Renal colic: waves of severe flank pain as peristalsis pushes against a stone; distension above it gives hydronephrosis.
- Bilateral obstruction (or one kidney) gives anuria and postrenal acute kidney injury; the ureterorenal reflex lowers flow on the blocked side.
- Urodynamics: a steep early curve means a small, poorly compliant bladder (neurogenic or fibrotic); unprovoked detrusor waves during filling mean detrusor overactivity.
- A non-compliant, high-pressure bladder transmits pressure to the ureters and can damage the kidneys even without reflux.
Test yourself
Think of the answer, then tap the question to see it.
What prevents urine from flowing back up the ureter when the bladder contracts?
The ureter crosses the detrusor obliquely; rising bladder pressure compresses the intramural segment, acting as a flap valve.
Why does a ureteric stone lower urine output from the affected kidney even before the pelvis fills?
Pain impulses trigger a sympathetic ureterorenal reflex that constricts renal arterioles and lowers GFR on that side, besides the back-pressure on filtration.
On a normal cystometrogram, why does pressure stay almost flat between about 100 and 300 mL?
The smooth-muscle wall relaxes as it stretches (stress relaxation) and the bladder unfolds, so volume rises with little rise in pressure (high compliance).
A child has recurrent pyelonephritis and a short intramural ureter. What is the link?
The short segment fails as a valve, so infected bladder urine refluxes up to the kidney during voiding (vesicoureteral reflux).
Connections
See it in 3D4
The structures of Durgical's 3D anatomy where it happens.
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: Anatomy, Abdomen and Pelvis Ureter (StatPearls (NCBI Bookshelf), 2025); Anatomy, Abdomen and Pelvis: Bladder (StatPearls (NCBI Bookshelf), 2025); Renal Calculi, Nephrolithiasis (StatPearls (NCBI Bookshelf), 2025); Kidney stones: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.