Urinary bladder

Vesica urinaria

Also known as: bladder, vesica

A hollow, distensible muscular reservoir in the anterior pelvis that stores urine at low pressure (capacity ≈400–600 mL) and expels it by detrusor contraction during micturition.

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Overview

Capacity≈400–600 mL

First sensation of filling≈150 mL

Filling pressure<10–15 cmH₂O

Normal post-void residual<50 mL

When empty the bladder is a three-sided pyramid lying entirely within the lesser pelvis behind the pubic symphysis; as it fills it becomes ovoid and rises into the abdomen, stripping the peritoneum off the anterior abdominal wall — so a full bladder can be punctured just above the pubic symphysis (suprapubic catheterisation) without entering the peritoneal cavity. In infants it is an abdominal organ.

It has an apex (directed toward the pubic symphysis and anchored to the umbilicus by the median umbilical ligament, the remnant of the urachus), a body, a fundus (base) facing posteriorly, and a neck where it joins the urethra. The neck is anchored by the pubovesical (female) or puboprostatic (male) ligaments. The interior is lined by urothelium thrown into rugae when empty except over the smooth trigone. The wall's smooth muscle is the detrusor; at the neck, circular fibres form the internal urethral sphincter (well developed in males).

The bladder fills at ≈1 mL/min, with little pressure rise (high compliance), until stretch receptors trigger the urge to void.

Location: Anterior lesser pelvis, posterior to the pubic symphysis; extraperitoneal (peritoneum covers only its superior surface).

Parts & subdivisions

Apex
Points toward the pubic symphysis; continuous with the median umbilical ligament (urachus).
Body
Main distensible part.
Fundus (base)
Posterior surface containing the trigone; related to the rectum (male) or vagina (female).
Neck
Lowest, most fixed part, continuous with the urethra; rests on the prostate in males.
Trigone
Smooth triangular area between the ureteric orifices and the internal urethral orifice.
Detrusor muscle
Interlacing smooth muscle forming the bladder wall.

Anatomy

Innervation: Parasympathetic: pelvic splanchnic nerves (S2–S4) — detrusor contraction. Sympathetic: T11–L2 via the superior and inferior hypogastric plexuses — detrusor relaxation (β3) and bladder-neck contraction (α1). Afferents: stretch (pelvic nerves, parasympathetic route) and pain from the superior surface (sympathetic route) to the cord.
Arterial supply: Superior vesical arteries (from the patent part of the umbilical artery, internal iliac) and inferior vesical arteries in males (vaginal arteries in females); minor branches from obturator and inferior gluteal arteries.
Venous drainage: Vesical venous plexus (continuous with the prostatic venous plexus in males) → internal iliac veins; communicates with the vertebral venous plexus (route for prostate cancer metastasis to the spine).
Lymphatic drainage: Mainly external iliac nodes (superolateral parts) and internal iliac nodes (neck and fundus).
Relations: Anterior: pubic symphysis and retropubic (prevesical/Retzius) space. Male posterior: seminal glands, ampullae of the ductus deferentes, rectum (rectovesical pouch); inferior: prostate. Female posterior: vagina and supravaginal cervix, uterus resting on its superior surface (vesicouterine pouch); inferior: pelvic floor (levator ani). Lateral: obturator internus and levator ani.
Histology: Urothelium with large dome-shaped umbrella cells whose apical uroplakin plaques make the barrier impermeable and fold away as the bladder distends; lamina propria; detrusor (three ill-defined smooth muscle layers); adventitia, with serosa on the superior surface.
Development: Upper (vesical) part of the urogenital sinus, from the cloaca; the trigone incorporates the caudal ends of the mesonephric ducts. The allantois becomes the urachus.

Function

Store urine at low pressure (continence)
Expel urine completely during micturition
Sense filling and signal the urge to void

Physiology: Capacity ≈400–600 mL; first sensation ≈150 mL; normal desire ≈200–300 mL; intravesical pressure stays <10–15 cmH₂O during filling; normal post-void residual <50 mL.

Clinical significance

Bladder rupture

Extraperitoneal rupture accompanies pelvic fractures (urine extravasates into the retropubic space and anterior abdominal wall); intraperitoneal rupture follows a blow to a full, distended bladder (dome tears; urine in the peritoneal cavity, requiring surgical repair).

Bladder cancer

Usually urothelial carcinoma, presenting with painless visible haematuria; risk factors: smoking (most important), aromatic amines (dye, rubber industries), cyclophosphamide; Schistosoma haematobium causes squamous cell carcinoma.

Urinary retention

Acute painful retention (BPH, anticholinergics, constipation, postoperative) is relieved by urethral or suprapubic catheterisation; chronic painless retention causes overflow incontinence and hydronephrosis.

Test yourself

A 40-year-old man has colicky loin-to-groin pain. At which site does a ureteric stone most commonly impact because the lumen is narrowest there?

Ureteropelvic junction
Where the ureter crosses the pelvic brim
Where the gonadal vessels cross the ureter
Ureterovesical junction

Answer: Ureterovesical junction

The three physiological narrowings are the ureteropelvic junction, the pelvic brim (crossing of the iliac vessels) and the ureterovesical junction; the intramural ureterovesical junction is the narrowest and the commonest site of impaction.

A man with a complete spinal cord transection at T6 develops a reflex bladder that contracts against a closed external sphincter. Which structure normally coordinates sphincter relaxation with detrusor contraction?

Pontine micturition centre
Sacral spinal cord (Onuf nucleus) alone
Hypothalamus
Cerebellum

Answer: Pontine micturition centre

The pontine micturition centre (Barrington nucleus) coordinates detrusor contraction with sphincter relaxation. Suprasacral cord lesions below the pons disconnect it, causing detrusor–sphincter dyssynergia with high bladder pressures.