Home > Topics > Changes in explanation of Nov 09 Q no. 10; answer remains the same – AA

Changes in explanation of Nov 09 Q no. 10; answer remains the same – AA

October 2, 2012

Correction in Nov 09 Q no. 10; answer remains the same, explanation is
10.     Vaginal sphincter is formed by all except:
a)      Internal urethral sphincter
b)      External urethral sphincter
c)      Pubovaginalis
d)      Bulbospongiosus


10.     Ans is ‘a’ i.e. Internal urethral sphincter  [Ref: Moore’s
Anatomy 5/e p402; Anatomy at a glance By Omar Faiz, David Burns Moffa
p61; Gray’s Anatomy 40/e p1094-1096; BDC 4/e vol. 2 p393; Practical
guide to female pelvic medicine  By Gamal M. Ghoniem, G. Willy
There is no ‘internal urethral sphincter’ in females. It is present in
males at the bladder neck and proximal urethral. Its function is to
prevent retrograde ejaculation of semen into the bladder during the
time of ejaculation.
In males the detrusor muscle fibers of the bladder at the region of
bladder neck and proximal urethra are organized into internal urethral
sphincter which is under involuntary control.
In females the musculature surrounding the internal urethral orifice
of the bladder is not organized into an internal sphincter.
External urethral sphincter is present in both males and females.

Vaginal sphincter is formed by the fibres of pubococcygeus known as
pubovaginalis. There are other muscles also which contribute in
compressing the vaginal orifice.
The Bulbospongiosus muscle fibres run anteriorly on either side of the
vagina to attach to the corpora cavernosa of the clitoris and
posteriorly to perineal body. Bulbospongiosus in females acts to
constrict the vaginal orifice and express the secretions of greater
vestibular glands.
The external urethral sphincter is composed of 3 muscles – sphincter
urethrae, compressor urethrae, and urethrovaginalis sphincter (or
muscle); last 2 muscles found in females only.
When external urethral sphincter contracts to compress the urethra, it
compresses the vaginal orifice also.

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