Urinary Bladder: Anatomy, Relations, and Clinical Significance

Overview

The urinary bladder is a hollow, distensible muscular organ serving as the reservoir for urine. Its capacity typically ranges from 300–500 mL, though it can accommodate more with pathological distension. In the empty state it is a tetrahedral structure; when filled, it becomes spherical and may rise into the abdominal cavity above the symphysis pubis — a clinically important point for suprapubic access.

Position and Relations

Empty Bladder

Located entirely within the lesser pelvis, just behind the pubic symphysis:

• Anterior: retropubic space (cave of Retzius); prevesical fat and loose connective tissue
• Superior: peritoneum overlies it; small bowel may lie on top
• Posterior (male): seminal vesicles, vasa deferentia, and rectum (rectovesical pouch separates bladder from rectum)
• Posterior (female): vagina (vesicovaginal septum); uterus (vesicouterine pouch)
• Inferior (male): prostate gland surrounds the bladder neck and urethra
• Inferior (female): urogenital diaphragm and levator ani

Full Bladder

Rises above the symphysis pubis into the hypogastric region, elevating the peritoneum and allowing suprapubic approaches without entering the peritoneal cavity.

Gross Anatomy

Parts

1. Apex: directed anterosuperiorly; from it the median umbilical ligament (urachus remnant) runs to the umbilicus
2. Body: main part between apex and fundus
3. Fundus (base): posteroinferior; triangular area facing posteriorly; contains the trigone
4. Neck: most fixed part; rests on the urogenital diaphragm (male) or pelvic floor (female); contains the internal urethral orifice

Trigone

The trigone is the smooth, triangular area at the base of the bladder:

• Bounded by the two ureteric orifices superolaterally and the internal urethral orifice inferiorly
• Unlike the rest of the bladder mucosa (which is rugose when empty), the trigone is always smooth (derived from incorporated mesonephric duct tissue)
• The interureteric ridge connects the two ureteric orifices
• Clinically important: tumors and infections frequently arise at the trigone; cystoscopy evaluates the trigone and ureteric orifices

Wall Structure

The bladder wall consists of:

1. Mucosa: transitional epithelium (urothelium); highly distensible
2. Submucosa: loose connective tissue with elastin
3. Muscularis (detrusor muscle): interlacing smooth muscle fibers in three layers (inner longitudinal, middle circular, outer longitudinal); not anatomically distinct except at the neck
4. Adventitia/Serosa: fibrous coat covering most; peritoneum covers only the superior surface

Internal Urethral Sphincter

Formed by the circular detrusor fibers at the bladder neck:

• Male: well-developed; smooth muscle; involuntary; sympathetically controlled (α-adrenergic); also prevents retrograde ejaculation
• Female: less distinct; continence relies more on external sphincter and pelvic floor

Blood Supply

• Superior vesical arteries: from the patent part of the umbilical artery (branch of internal iliac)
• Inferior vesical artery (male) / vaginal arteries (female): from internal iliac
• Obturator and inferior gluteal arteries: minor contribution
• Venous: vesical venous plexus → internal iliac veins

Lymphatic Drainage

• External iliac nodes: superior bladder
• Internal iliac nodes: posterior and inferior bladder
• Obturator nodes: anterolateral

Innervation

• Parasympathetic (pelvic splanchnic nerves, S2–S4): detrusor contraction, internal sphincter relaxation (micturition)
• Sympathetic (hypogastric nerve, T11–L2): detrusor relaxation (filling), internal sphincter contraction (storage)
• Somatic (pudendal nerve, S2–S4): external urethral sphincter (voluntary control)
• Sensory: stretch receptors trigger conscious desire to void at ~150 mL

Micturition (Voiding)

Controlled by the pontine micturition center:

1. Detrusor contracts (parasympathetic)
2. Internal sphincter relaxes (sympathetic withdrawal)
3. External sphincter relaxes (somatic withdrawal = voluntary)
4. Urine flows out

Clinical Relevance

• Bladder cancer: urothelial (transitional cell) carcinoma most common; painless hematuria; smoking is the major risk factor; trigone/posterior wall most frequent location
• Cystitis: bacterial infection; dysuria, frequency, suprapubic pain; Escherichia coli most common pathogen
• Neurogenic bladder: upper motor neuron (spastic) vs. lower motor neuron (flaccid); requires catheterization or other management
• Bladder exstrophy: congenital failure of anterior bladder wall closure; exposed bladder mucosa
• Suprapubic catheterization: possible when full bladder rises above pubis, avoiding peritoneal cavity

Study Points

• Describe the position of the full vs. empty bladder and explain the clinical significance for suprapubic access.
• Define the trigone: boundaries, histological distinctiveness, and clinical importance.
• Trace the neural control of micturition through the three components of the sphincter mechanism.
• Describe the blood supply to the bladder from the internal iliac system.
• Explain the pathophysiology of upper vs. lower motor neuron bladder dysfunction.