856
UNIT SIX
the arteries associated with the erectile tissues. As a result,
blood infl ow increases, tissues swell, and the vagina expands
and elongates.
If sexual stimulation is sufficiently intense, parasym-
pathetic impulses stimulate the vestibular glands to secrete
mucus into the vestibule. This secretion moistens and lubri-
cates the tissues surrounding the vestibule and the lower
end of the vagina, facilitating insertion of the penis into the
vagina. Mucus secretion continuing during sexual inter-
course helps prevent irritation of tissues that might occur if
the vagina remained dry.
The clitoris is abundantly supplied with sensory nerve
F
bers, which are especially sensitive to local stimulation.
The culmination of such stimulation is orgasm, the pleasur-
able sensation of physiological and psychological release.
Just prior to orgasm, the tissues of the outer third of
the vagina engorge with blood and swell. This increases the
friction on the penis during intercourse. Orgasm initiates a
series of refl
exes involving the sacral and lumbar parts of the
spinal cord. In response to these refl exes, the muscles of the
perineum and the walls of the uterus and uterine tubes con-
tract rhythmically. These contractions help transport sperm
cells through the female reproductive tract toward the upper
ends of the uterine tubes
(f
g. 22.31)
.
±ollowing orgasm, the fl
ow of blood into the erectile tis-
sues slackens, and the muscles of the perineum and repro-
ductive tract relax. Consequently, the organs return to a
state similar to that prior to sexual stimulation.
Table 22.2
summarizes the functions of the female reproductive organs.
PRACTICE
44
What events result from parasympathetic stimulation of the
female reproductive organs?
45
What changes occur in the vagina just prior to and during female
orgasm?
46
How do the uterus and the uterine tubes respond to orgasm?
including a portion embedded in surrounding tissues. The
clitoris corresponds to the penis and has a similar structure.
It is composed of two columns of erectile tissue called
cor-
pora cavernosa.
A septum separates these columns, which
are covered with dense connective tissue.
At the root of the clitoris, the corpora cavernosa diverge
to form
crura,
which, in turn, attach to the sides of the pubic
arch. At its anterior end, a small mass of erectile tissue forms
a glans, which is richly supplied with sensory nerve F
bers.
Vestibule
The labia minora enclose the space called the
vestibule.
The
vagina opens into the posterior portion of the vestibule, and
the urethra opens in the midline, just anterior to the vagina
and about 2.5 centimeters posterior to the glans of the clitoris.
A pair of
vestibular glands
(Bartholin’s glands), cor-
responding to the bulbourethral glands in the male, lie on
either side of the vaginal opening. Their ducts open into the
vestibule near the lateral margins of the vaginal oriF
ce.
Beneath the mucosa of the vestibule on either side is a
mass of vascular erectile tissue. These structures are called
the
vestibular bulbs.
They are separated from each other by
the vagina and the urethra, and they extend forward from
the level of the vaginal opening to the clitoris.
PRACTICE
42
What is the male counterpart of the labia majora? Of the clitoris?
43
Which structures are within the vestibule?
Erection, Lubrication, and Orgasm
Erectile tissues in the clitoris and around the vaginal entrance
respond to sexual stimulation. ±ollowing such stimulation,
parasympathetic nerve impulses from the sacral portion of
the spinal cord release the vasodilator nitric oxide, dilating
FIGURE 22.31
Mechanism of erection, lubrication, and orgasm in the female.
Sexual stimulation
Sexual stimulation intensifies
Parasympathetic nerve impulses from the
sacral portion of the spinal cord
Arteries in the erectile tissue dilate; vagina
expands and elongates
Engorged and swollen vagina increases
friction from movement of the penis
Vestibular glands secrete mucus to lubricate
Orgasm—rhythmic contraction of muscles
of the perineum; muscular walls of
uterus and uterine tubes contract
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