Bladder Anatomy
The urinary bladder stores urine and initiates micturition. Its anatomical regions, relations, and the trigone are essential for understanding cystoscopy, bladder cancer staging, and pelvic surgery.
✦ The Mnemonic
"Apex, Body, Fundus, Neck — Always Triangulate"
Apex · Body · Fundus (base) · Neck — four regions + Trigone
Clinical Breakdown
The bladder is an extraperitoneal pelvic organ (when full it rises into the abdomen). Its superior surface is covered by peritoneum — a full bladder can be punctured above the pubic symphysis for suprapubic catheterisation without entering the peritoneal cavity. Relations: anterosuperiorly the pubic symphysis; posteriorly the rectum (M) or uterus/vagina (F).
The trigone is smooth (unlike the rugose body) because it has a different embryological origin — it is derived from the incorporated lower ends of the mesonephric ducts (Wolffian ducts). It is the most sensitive area of the bladder and the most common site for bladder tumours (transitional cell carcinoma).
Bladder cancer: transitional cell carcinoma (TCC/urothelial carcinoma) accounts for 90%. Risk factors: smoking (most important), aniline dyes, cyclophosphamide, schistosomiasis (squamous cell type). Painless haematuria is the cardinal presentation — any episode warrants urgent cystoscopy. Superficial tumours (Ta/T1) are managed endoscopically; muscle-invasive (T2+) require cystectomy or radical radiotherapy.
⭐ Clinical Pearl
Urethral sphincters: the internal urethral sphincter (smooth muscle, autonomic — sympathetic α1) maintains continence at rest. The external urethral sphincter (skeletal muscle, somatic — pudendal nerve, S2–S4) provides voluntary control. In spinal cord injury above S2, both sphincters can be dyssynergic — detrusor-sphincter dyssynergia prevents voiding despite a contracting detrusor.