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Male Internal Urethral Sphincter (Posterior Part)
Urogenital System

Male Internal Urethral Sphincter (Posterior Part)

Sphincter internus urethrae masculinae

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The male internal urethral sphincter is a circular sphincter muscle consisting entirely of smooth muscle.

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Key Features/Anatomical Relations

The internal urethral sphincter represents the junction between the urinary bladder (superiorly) and the urethra (inferiorly).


This sphincter is under involuntary control and is tonically contracted due to sympathetic innervation from the lumbar plexus. During urination, the pelvic splanchnic nerves (parasympathetic) cause the internal urethral sphincter to relax allowing urine to pass from the bladder to the urethra.

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Urethral Sphincter

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Urethral sphincter dysfunction which is due to various causes including weakness of the muscles and ligaments around the bladder neck, descent of the urethrovesical junction and periurethral fibrosis;

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