A hollow sac behind the pubic symphysis that holds about 400 to 600 mL and rises out of the pelvis when full
Urinary bladder — it becomes an abdominal organ when distended.
Anatomy · Organs & viscera
Urinary bladder
Holds about 400 to 600 mL
Pelvis · urinary system
The urinary bladder is a hollow, muscular, distensible sac in the pelvis that stores urine between voidings. When empty it lies behind the pubic symphysis, shaped like a three-sided pyramid; when full it swells upwards into the lower abdomen. The two ureters enter at the back and the urethra leaves at the lowest point, the neck, and the smooth triangle between these three openings is the trigone.
How to spot them
- ▸A pyramid-shaped sac behind the pubic bones when empty, rising into the abdomen like a dome when full
- ▸Apex pointing forwards to the top of the pubic symphysis, linked to the umbilicus by the median umbilical ligament
- ▸Behind it: rectum, seminal vesicles and vasa deferentia in men; uterus and vagina in women
- ▸Inside, a smooth triangular area called the trigone between the two ureteric openings and the urethral opening
What to know
The smooth-walled triangle inside, between the openings of the two ureters and the urethra, that stays flat whatever the fullness
The trigone of the bladder.
The thick muscle wall that contracts to empty the organ, made of interlacing smooth muscle bundles
The detrusor muscle of the bladder.
A fibrous cord running from its apex up to the navel, the remnant of the foetal urachus
The median umbilical ligament, from the bladder's apex.
Lined with a stretchy transitional epithelium that flattens as it fills
The urothelium of the bladder.
A needle can be passed into it just above the pubic bone without entering the peritoneal cavity when it is distended
Suprapubic catheterisation of the bladder — the peritoneum is lifted upwards.
Lies in front of the rectum in men, with the seminal vesicles between, and in front of the vagina and beneath the uterus in women
The relations of the bladder, male and female.
Key ideas
- The bladder is under the control of the parasympathetic pelvic splanchnic nerves (S2 to S4), which contract the detrusor for emptying, and sympathetic fibres that help storage.
- Stretch receptors signal the desire to void at about 200 to 300 mL, but the organ can hold considerably more.
Quick-fire facts
- •Capacity is roughly 400 to 600 mL, and the urge to pass urine typically begins at 200 to 300 mL.
- •When empty it is a pelvic organ behind the pubic symphysis; in young children it lies higher in the abdomen.
- •It has an apex, a base (posterior surface), a neck, a superior surface and two inferolateral surfaces.
- •Only its superior surface is covered by peritoneum in the adult, which is why a full bladder can be reached above the pubis.
- •The internal urethral sphincter at the neck is involuntary and best defined in men; the external urethral sphincter is voluntary.
- •The trigone is usually said to have a different embryological origin (mesoderm, from the mesonephric ducts) from the rest of the bladder lining.
- •Its wall is made of urothelium, lamina propria, the muscle layer (detrusor) and an outer adventitia or serosa.
- •In men, the prostate surrounds the neck; enlargement of it can obstruct outflow.
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