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  • Detrusor: “Bladder muscle”—smooth muscle; innervation is parasympathetic (muscarinic acetylcholine—M2, M3; contraction) and sympathetic (β3-adrenergic receptors; detrusor inhibition or relaxation) (Figure 5-1)

  • Urethral sphincter

    • Internal urethral sphincter (IUS): Smooth muscle; sympathetic (α1) innervation; muscarinic acetylcholine, α- and β-adrenergic receptors

    • External urethral sphincter (EUS): Striated muscle; somatic motor innervation via pudendal nerve (S2–S4); nicotinic acetylcholine receptors

    • Submucosal endovascular cushions

    • Surrounding tissue support—hammock hypothesis—the anterior vaginal wall with its attachment to the arcus tendineus of the pelvic fascia forms a hammock of tissue under the urethra and bladder neck that prevents urethral and bladder neck descent, such that the urethra compresses shut with increased intra-abdominal pressure

Figure 5-1

Anteroposterior view of bladder anatomy. (Used with permission from Hoffman BL, Schorge JO, Schaffer JI, Halvorson LM, Bradshaw KD, Cunningham F, Calver LE. Chapter 23. Urinary incontinence. In: Hoffman BL, Schorge JO, Schaffer JI, Halvorson LM, Bradshaw KD, Cunningham F, Calver LE, eds. Williams Gynecology. 2nd ed. New York, NY: McGraw-Hill; 2012.)


  • Bladder filling = SYMPATHETIC = “STORAGE”

    • L1–L3 → lumbar sympathetic ganglia → forms hypogastric nerve to pelvis

    • Norepinephrine released → decreases smooth muscle tone in bladder

      • Relaxation of detrusor muscle: β3-adrenergic receptors in bladder stimulated (bladder fills)

      • Contraction of IUS: α-Adrenergic receptors in IUS stimulated (sphincter tightens)

      • Contraction of EUS by trained voluntary action (pudendal nerve originates from S2 to S4 to innervate EUS and perineal muscles—acetylcholine)

  • Micturition (emptying of bladder) = PARASYMPATHETIC = “PEEING”

    • Full bladder sensed by mechano-receptors in bladder

    • S2–S4 → sacral spinal cord → forms pelvic nerve

    • Stimulates bladder using acetylcholine and relaxes the urethra employing nitric oxide

      • Contraction of detrusor muscle: Muscarinic cholinergic (M3) receptors stimulated (bladder contracts)

      • Relaxation of IUS: M3 receptors stimulated (sphincter relaxes)

      • Relaxation of EUS by trained voluntary action (pudendal nerve originates from S2–S4—acetylcholine)



Involuntary loss of urine. Prevalence in the United States is about 50% of adult women.


  • Stress urinary incontinence (SUI): Most common type (50–70% of UI)

    • Involuntary leakage during effort, exertion, sneezing, or coughing

    • Risk factors include age, parity, vaginal delivery

    • Leakage with stress test. Bladder capacity and post-void residual (PVR) normal (PVR generally considered normal if <150 cc or <1/3 void volume)

    • Urethral hypermobility (straining angle ≥30 degrees on Q-tip test) present in many women with SUI

    • Urodynamic SUI: During filling cystometry, involuntary urine leakage with increased intra-abdominal pressure and without detrusor contraction

  • Urge incontinence

    • Leakage accompanied by or immediately preceded by urge to void

    • Typically results from sudden, involuntary detrusor contractions

    • Usually idiopathic; but can be from inflammation/irritation, calculi, neurologic disorders, outlet obstruction, increased urine output

    • Urodynamics: If detrusor contractions are seen on ...

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