Urinary bladder and urethra

Shape, surfaces and relations

• When empty, a pyramid behind the symphysis. Apex points to the umbilicus (attached by the median umbilical ligament, the urachus remnant); superior surface covered by peritoneum; base (posterior surface); inferolateral surfaces face the retropubic space; neck held by pubovesical (puboprostatic in men) ligaments.
• As it fills it rises and strips peritoneum off the abdominal wall, so a suprapubic catheter just above the pubis stays extraperitoneal. In infants the bladder lies mainly in the abdomen.

• Faecaluria in a man means a vesicocolic or rectovesical fistula through the rectovesical pouch or Denonvilliers fascia; in a woman the uterus usually lies between bladder and colon.
• Injury: a blow to a full bladder tears the dome (intraperitoneal). A pelvic fracture causes extraperitoneal rupture.

Interior, lining and blood supply

• Trigone: between the two ureteric orifices and the internal urethral orifice, its upper border the interureteric ridge. Its mucosa is smooth and fixed to muscle; it develops from the mesonephric ducts. The rest of the lining is urogenital sinus endoderm, folded when empty.
• Urothelium: the barrier that keeps hypertonic urine and urea out of the blood is the uroplakin plaques of the superficial umbrella cells, sealed by tight junctions.
• Detrusor: interlacing smooth muscle; highly compliant, so 50–400 mL produces little pressure rise, protecting the kidneys.
• Arteries: superior vesical (from the patent part of the umbilical artery) and the inferior vesical (men) or vaginal arteries (women) to the base and neck. In men the inferior vesical gives the prostatic arteries, which enter at the bladder neck at about 5 and 7 o'clock: the bleeding points at transurethral prostate resection.
• Veins: vesical venous plexus (home of Schistosoma haematobium). Lymph: mainly external iliac, also internal iliac.

Urethra

• Female: about 4 cm, from the bladder neck through the urogenital hiatus and perineal membrane to the vestibule; fused to the lower anterior vaginal wall. There is no strong smooth muscle internal sphincter; the striated urethral sphincter complex in the deep pouch is thickest at the mid-urethra, where mid-urethral tapes are placed.
• The mucosa and submucosal venous plexus form an oestrogen-dependent seal; vaginal oestrogen improves stress leakage by restoring this seal, not by strengthening muscle.
• Male: prostatic, membranous (in the deep pouch, through the external sphincter, with the bulbourethral glands beside it), and spongy (bulbar and penile).

• The thighs are spared because Colles fascia fuses with the fascia lata.

Nerve supply and receptors

• The internal sphincter (bladder neck smooth muscle) is sympathetic; in men it closes during ejaculation to prevent retrograde flow. The external sphincter is pudendal.
• Pain: distension of the dome travels with sympathetic afferents to T11–L2; the base and neck use S2–S4 afferents.
• Loss of bladder sensation (diabetic neuropathy, tabes) gives a large, atonic, overflowing bladder with residual urine.
• Sacral root lesions cause retention: radical hysterectomy damaging the inferior hypogastric plexus, or primary genital herpes causing sacral radiculitis of S2–S4 (retention, constipation, reduced perianal sensation).

Micturition and continence

• Filling: sympathetic relaxation plus a guarding reflex that increases pudendal firing.
• Voiding: a spinobulbospinal reflex coordinated by the pontine micturition centre and released voluntarily by the cortex. The sphincter relaxes first, then the detrusor contracts.
• Stress incontinence: the bladder neck descends below the pelvic floor (childbirth, menopause), so abdominal pressure no longer reaches the urethra; the detrusor is stable.
• Detrusor overactivity: involuntary contractions during filling, causing urgency and urge leakage.
• Nocturia in late pregnancy: oedema fluid from the legs returns to the circulation on lying down and is excreted at night.
• Postpartum retention: epidural and perineal pain blunt the urge; overdistension injures the detrusor.

Drugs acting on the bladder

Infection and inflammation

• Uropathogenic E. coli attach to the urothelium mainly by type 1 (mannose-binding) fimbriae; P fimbriae are the kidney adhesin.
• The short female urethra near the vagina and anus explains post-coital cystitis.
• After the menopause loss of oestrogen depletes vaginal lactobacilli, the pH rises (above 4.5) and colonising coliforms cause recurrent UTI; local oestrogen helps.
• Nitrofurantoin is avoided at term because it can cause haemolytic anaemia in the newborn (immature red cell enzymes).
• Malakoplakia: soft yellow plaques in immunosuppressed patients with E. coli infection; foamy macrophages with laminated calcified Michaelis–Gutmann bodies from defective bacterial killing.
• Radiation cystitis: years after radiotherapy, obliterative endarteritis causes ischaemic fibrosis and fragile telangiectasia that bleed.

Bladder tumours and endometriosis

• Urothelial (transitional cell) carcinoma is the commonest bladder cancer. Risks: smoking (strongest), aromatic amines in aniline dye and rubber work (2-naphthylamine, benzidine), cyclophosphamide (acrolein), phenacetin.
• Squamous cell carcinoma: Schistosoma haematobium, chronic stones and indwelling catheters (squamous metaplasia). Adenocarcinoma: urachal remnant at the dome.
• Carcinoma in situ: flat, high-grade malignant urothelium with an intact basement membrane.
• Bladder endometriosis: cyclical dysuria and haematuria during menstruation, with a bluish nodule on the posterior wall.

Fistulas and urinary leaks

• Vesicovaginal: obstructed labour presses the bladder base against the symphysis; continuous leakage 7–14 days later.
• Vesicouterine: after repeat caesarean section; cyclical haematuria with apparent amenorrhoea.
• Urinary ascites after bladder or ureteric injury: ascitic creatinine far above serum. Serum creatinine rises because the peritoneum reabsorbs urinary creatinine (pseudo-renal failure); the kidneys are normal.

Remember Sympathetic stores (beta-3 relaxes, alpha-1 closes), parasympathetic empties (M3 contracts), pudendal holds on.

Exam trap The trigone is smooth because its mucosa is fixed to muscle; it comes from the mesonephric ducts, not the urogenital sinus.

Exam trap Bulbar urethral rupture spreads to the scrotum and abdominal wall but not the thighs; membranous rupture stays in the pelvis.

How FCPS asks about this

• Micturition is controlled by: parasympathetic S2–S4 (M3 detrusor contraction), coordinated by the pontine micturition centre.
• Nerve to internal and external urethral sphincters: internal, sympathetic (alpha-1); external, pudendal nerve S2–S4.
• Structures behind the male bladder, lateral to medial: seminal vesicle, then ampulla of the vas deferens.
• Bleeding at 5 and 7 o'clock during TURP: prostatic branches of the inferior vesical arteries.
• Fall astride with scrotal and abdominal wall swelling, thighs spared: bulbar urethra below the perineal membrane.
• Commonest bladder cancer and its causes: urothelial carcinoma; smoking and aniline dye amines; schistosomiasis causes squamous carcinoma.
• Barrier of the bladder lining: uroplakin plaques of umbrella cells with tight junctions.