internal urethral sphincter

(redirected from proximal urethral sphincter)

in·ter·nal u·re·thral sphinc·ter

the complete collar of smooth muscle cells of the neck of the urinary bladder that extends distally to surround the preprostatic portion of the male urethra. There is no comparable structure in the neck of the female bladder; the internal urethral sphincter may exist to prevent reflux of semen into the bladder.
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