Urinary Bladder: Anatomy, Physiology & Clinical Relevance

Anatomy

• Location: Retropubic, extraperitoneal, posterior to pubic symphysis.
• Structure: Detrusor muscle (smooth muscle: longitudinal–circular–longitudinal), mucosa (transitional epithelium/urothelium), trigone (fixed, sensitive).
• Innervation: Parasympathetic (S2–S4 pelvic splanchnics → contraction), Sympathetic (T11–L2 hypogastric → relaxation), Somatic (S2–S4 pudendal → external urethral sphincter).
• Capacity: 300–500 mL adults; first urge ~150 mL, strong urge ~300 mL.

Physiology of Micturition

1. Filling phase: Sympathetic tone relaxes detrusor, contracts internal sphincter; pudendal maintains external sphincter tone.
2. Storage: Compliance allows low-pressure filling.
3. Voiding phase: Pontine micturition center (PMC) triggered → parasympathetic surge contracts detrusor, inhibits sphincters → flow.

Common Disorders

• Overactive bladder (OAB) – urgency, frequency, urge incontinence.
• Underactive bladder / detrusor underactivity – high PVR, recurrent UTI.
• Bladder outlet obstruction (BPH, stricture, prolapse).
• Neurogenic bladder (SCI, MS, spina bifida).
• Interstitial cystitis / bladder pain syndrome.
• Bladder cancer (urothelial carcinoma).

Diagnostic Tools

• Urinalysis, culture, cytology.
• Urodynamics (cystometry, pressure-flow study).
• Cystoscopy (visualize mucosa, biopsy).
• Imaging: US (PVR, wall thickness), CT/MRI (staging).