Urethral sphincters by alphauro

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									Urethral sphincters

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Types
1.

Smooth sphincter. Striated sphincter.

2.

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Smooth sphincter.
 Is

a thin smooth muscle layer that extends along the entire urethra in the female and throughout the prostate and its capsule in the male.

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Striated (external) urethral sphincter


The striated sphincter is actually signet ring– shaped, broad at its base, and narrowing as it passes through the urogenital hiatus of the levator ani to meet the apex of the prostate.

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Cont,


At the apex of the prostate, circular fibers surround the urethra, and they thin posteriorly to insert into a fibrous raphe.  Distally, the fibers do not meet posteriorly; rather, they acquire an Ω shape as they fan out laterally over the perineal membrane.  Throughout its length, the posterior portion of the striated sphincter inserts into the perineal body.
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Cont,
 Relations

:

Anteriorly to the dorsal vein complex (which may invade its anterior portion with age).
Laterally to the levator ani.

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Cont,
 Despite

the horseshoe configuration, urethral pressure recording at the external sphincter during bladder filling increases uniformly along the entire circumference like an iris.

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Cont,


The female has an attenuated striated sphincter mechanism as well as additional muscular structures: compressor urethrae. urethrovaginal sphincter. This attenuation of distal sphincteric muscles may contribute to urinary incontinence in females after resection of the bladder neck.
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•

Fiber Types of Urethral Striated Muscle
 



Striated muscles are characterized as twitch-type: Fast-twitch fibers: can be recruited rapidly. tend to fatigue rapidly. perform predominantly anaerobic metabolism. Slow-twitch fibers: recruited and fatigue slowly. can perform high rates of oxidative metabolism.
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Cont,
 1)

2)

The external urethral sphincter is composed of two parts: The periurethral striated muscle of the pelvic floor contains both fast- and slow-twitch fibers. . The striated muscle of the distal sphincter mechanism contains predominantly slowtwitch fibers (provides greater than 50%

of the static resistance).
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Cont,
 In

the male, the rhabdosphincter consists of 35% fast-twitch and 65% slow-twitch fibers

 In

the female, the ratio of slow- to fasttwitch fibers is 87% slow twitch and 13% fast twitch.

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Nerve supply
 The

striated sphincter :
 The pudendal nerve.  A branch of the sacral plexus that runs on the pelvic surface of the levator ani.

 Smooth

sphincter :
 the cavernous nerves

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