THE VAGINA
The vagina (from Latin, literally “sheath” or “scabbard”) serves as the portal to the internal female reproductive tract and a route of egress for the fetus during delivery. The viscera contained within the female pelvis minor include the pelvic colon, urinary bladder and urethra, uterus, uterine tubes, ovaries, and vagina. These structures surround the vagina and interact with it in the clinical setting. Therefore, the vagina also provides a convenient portal to understanding the female pelvic viscera.
The vagina is a thin-walled, distensible, fibromuscular canal, covered by
specialized epithelium, which extends from the vulva inward to the cervix and
uterus. Under normal circumstances, the vagina is a potential space that is
larger in the middle and upper thirds, giving it an inverted pear- or T-shape
when viewed perpendicular to its long axis. The walls of the vagina are
normally flattened in the anteroposterior diameter, giving the appearance of the
letter H in cross section. In its distal extreme, the vagina opens to the vulva
at the hymenal ring, opening at the caudal end of the vulva, behind the opening
of the urethra. When upright, the vaginal tube points in an upward–backward
direction with the axis of the upper portion of the vagina in close to the
horizontal plane, curving toward the hollow of the sacrum. In most women, an
angle of at least 90° is formed between the vagina and the uterus. The cervix
is directed downward and backward to rest against the posterior vaginal wall.
The spaces between the cervix and attachment of the vagina are called fornices,
with the posterior fornix considerably larger than the anterior fornix.
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Although there is wide variation, the length of the vagina is
approximately 6 to 9 cm (2.5 to 3.5 in.) along the anterior wall and 8 to 12 cm
(3 to 4.5 in.) along the posterior wall. During sexual arousal, the upper
portion of the vagina elongates and widens through a relative upward movement
of the uterus and cervix. This is thought to facilitate capture and retention
of sperm to enhance the chance of conception.
Throughout most of its length, the vagina lies directly on top of the
descending rectum, separated by the rectovaginal septum. The upper one-fourth
of the vagina is separated from the rectum by the rectouterine pouch (posterior
cul-de-sac). The urethra and base of the urinary bladder lie above the anterior
vaginal wall separated by the thin layers of endopelvic fascia. As they enter
the bladder, the ureters pass forward and medial-ward close to the lateral
fornices.
The vagina is held in position by the surrounding endopelvic fascia and
ligaments: The lower third of the vagina is surrounded and supported by the
urogenital and pelvic diaphragms. The levator ani muscles and the lower portion of the cardinal ligaments support the middle third of
the vagina, whereas portions of the cardinal ligaments and the parametria
support the upper third.
The vagina is supplied by an extensive anastomotic network of vessels
that surround its length. The vaginal artery originates either directly from
the uterine artery or as a branch of the internal iliac artery arising
posterior to the origin of the uterine and inferior vesical arteries. There is an anastomosis with the descending cervical branch of
the uterine artery to form the azygos arteries. Branches of the internal
pudendal, inferior vesical, and middle hemorrhoidal arteries also contribute to
the interconnecting network from below. These can be a significant source of
bleeding with obstetric lacerations. They are also important in the development
of vaginal transudate during sexual arousal, when the vagina produces
lubrication to aid in penetration.
