1040
UNIT 5
Continuity
27
birth canal
, the vagina provides a passageway for delivery of
an infant and for menstrual flow. Because it receives the penis
(and semen) during sexual intercourse, it is the
female organ of
copulation
.
Te distensible wall of the vagina consists of three coats: an
outer fibroelastic
adventitia
, a smooth muscle
muscularis
, and
an inner
mucosa
marked by transverse ridges or rugae, which
stimulate the penis during intercourse. Te mucosa is a stratified
squamous epithelium adapted to stand up to friction.
Dendritic
cells
in the mucosa act as antigen-presenting cells and are thought
to provide the route of HIV transmission from an infected male
to the female during sexual intercourse. (Chapter 21 describes
AIDS, the immune deficiency disease caused by the HIV virus.)
Te vaginal mucosa has no glands. Instead, it is lubricated
by the cervical mucous glands and the mucosal transudate
that “weeps” from the vaginal walls. Its epithelial cells release
large amounts of glycogen, which resident bacteria metabolize
anaerobically to lactic acid. Consequently, the pH of a woman’s
vagina is normally quite
acidic
. Tis acidity helps keep the va-
gina healthy and free of infection, but it is also hostile to sperm.
Although vaginal fluid of adult females is acidic, it tends to be
alkaline in adolescents, predisposing sexually active teenagers
to sexually transmitted infections.
In virgins (those who have never participated in sexual
intercourse), the mucosa near the distal
vaginal orifice
forms
an incomplete partition called the
hymen
(hi
9
men)
(Fig-
ure 27.16a)
. Te hymen is very vascular and may bleed when
it stretches or ruptures during the first coitus (sexual inter-
course). However, its durability varies. In some females, it
is ruptured by sports, inserting tampons, or pelvic examina-
tions. Occasionally, it is so tough that it must be breached
surgically if intercourse is to occur.
Te upper end of the vaginal canal loosely surrounds the
cervix of the uterus, producing a vaginal recess called the
vagi-
nal fornix
. Te posterior part of this recess, the
posterior for-
nix
, is much deeper than the
lateral
and
anterior fornices
(see
Figures 27.12 and 27.14). Generally, the lumen of the vagina is
quite small and, except where the cervix holds it open, its pos-
terior and anterior walls touch each other. Te vagina stretches
considerably during copulation and childbirth, but its lateral
distension is limited by the ischial spines and the sacrospinous
ligaments.
Homeostatic Imbalance
27.7
Te uterus tilts away from the vagina. For this reason, attempts
by untrained persons to induce an abortion by entering the
uterus with a surgical instrument may puncture the posterior
wall of the vagina. Tis causes hemorrhage and—if the instru-
ment is unsterile—peritonitis.
Check Your Understanding
22.
Why are women more at risk for PID than men?
23.
Oocytes are ovulated into the peritoneal cavity and yet
women do get pregnant. What action of the uterine tubes
helps to direct the oocytes into the woman’s duct system?
Pubic symphysis
Labia minora
Clitoris
Labia majora
Anus
Body of clitoris,
containing
corpora
cavernosa
Clitoris (glans)
Crus of clitoris
External
urethral orifice
Vaginal orifice
Greater
vestibular
gland
Fourchette
Bulb of
vestibule
Inferior
ramus
of pubis
Mons
pubis
Prepuce
of clitoris
Clitoris
(glans)
Vestibule
Anus
(a)
Labia
majora
Labia
minora
External
urethral
orifice
Hymen
(ruptured)
Opening of the duct
of the greater
vestibular gland
Vaginal
orifice
(b)
Figure 27.16
The external genitalia (vulva) of the female.
(a)
Superficial structures. The region enclosed by dashed lines is the
perineum.
(b)
Deep structures. The labia majora and associated skin
have been removed to show the underlying erectile bodies. For the
associated superficial muscles, see Figure 10.13 on p. 345.
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