Chapter 27
The Reproductive System
1041
27
The Female Perineum
Te female
perineum
is a diamond-shaped region located be-
tween the pubic arch anteriorly, the coccyx posteriorly, and the
ischial tuberosities laterally (Figure 27.16a). Te so± tissues of
the perineum overlie the muscles of the pelvic outlet, and the
posterior ends of the labia majora overlie the
central tendon
,
into which most muscles supporting the pelvic floor insert (see
²able 10.7).
Check Your Understanding
25.
What is the female homologue of the bulbo-urethral glands
of males?
26.
Cite similarities and differences between the penis and
clitoris.
For answers, see Appendix H.
The Mammary Glands
Discuss the structure and function of the mammary glands.
Te
mammary glands
are present in both sexes, but they nor-
mally function only in females
(Figure 27.17)
. Te biological
role of the mammary glands is to produce milk to nourish a
newborn baby, so they are important only when reproduction
has already been accomplished.
Developmentally, mammary glands are modified sweat
glands that are really part of the
skin
, or
integumentary system
.
Each mammary gland is contained within a rounded skin-
covered breast within the hypodermis (superficial fascia), anterior
to the pectoral muscles of the thorax. Slightly below the center of
each breast is a ring of pigmented skin, the
areola
(ah-re
9
o-lah),
which surrounds a central protruding
nipple
. Large sebaceous
glands in the areola make it slightly bumpy and produce sebum
that reduces chapping and cracking of the skin of the nipple. Au-
tonomic nervous system controls of smooth muscle fibers in the
areola and nipple cause the nipple to become erect when stimu-
lated by tactile or sexual stimuli, or cold temperatures.
Internally, each mammary gland consists of 15 to 25
lobes
that radiate around and open at the nipple. Te lobes are pad-
ded and separated from each other by fibrous connective tis-
sue and fat. Te interlobar connective tissue forms
suspensory
ligaments
that attach the breast to the underlying muscle fascia
and the overlying dermis. As suggested by their name, the sus-
pensory ligaments provide natural support for the breasts, like
a built-in brassiere.
Within the lobes are smaller units called
lobules
, which con-
tain glandular
alveoli
that produce milk when a woman is lac-
tating. Tese compound alveolar glands pass the milk into the
lactiferous ducts
(lak-tif
9
er-us), which open to the outside at the
nipple. Just deep to the areola, each duct has a dilated region called
a
lactiferous sinus
where milk accumulates during nursing. We
describe the process and regulation of lactation in Chapter 28.
Te description of mammary glands that we have just given
applies only to nursing women or women in the last trimester
of pregnancy. In nonpregnant women, the glandular structure
24.
What portion of the female duct system is the usual
site of fertilization? Which is the “incubator” for fetal
development?
For answers, see Appendix H.
The External Genitalia
Describe the anatomy of the female external genitalia.
Te female reproductive structures that lie external to the vagina
are called the
external genitalia
(Figure 27.16). Also called the
vulva
(vul
9
vah; “covering”) or
pudendum
(“shameful”), these
structures include the mons pubis, labia, clitoris, and structures
associated with the vestibule.
Te
mons pubis
(mons pu
9
bis; “mountain on the pubis”)
is a fatty, rounded area overlying the pubic symphysis. Af-
ter puberty, this area is covered with pubic hair. Running
posteriorly from the mons pubis are two elongated, hair-
covered fatty skin folds, the
labia majora
(la
9
be-ah mah-
jor
9
ah; “larger lips”). Tese are the counterpart, or homo-
logue, of the male scrotum (that is, they derive from the
same embryonic tissue). Te labia majora enclose the
labia
minora
(mi-nor
9
ah; “smaller”), two thin, hair-free skin folds,
homologous to the ventral penis.
Te labia minora enclose a recess called the vestibule (“en-
trance hall”), which contains the external openings of the
urethra and the vagina. Flanking the vaginal opening are the
pea-size
greater vestibular glands
, homologous to the bulbo-
urethral glands of males (Figure 27.16b). Tese glands release
mucus into the vestibule and help to keep it moist and lubri-
cated, facilitating intercourse. At the extreme posterior end of
the vestibule the labia minora come together to form a ridge
called the
fourchette
.
Just anterior to the vestibule is the
clitoris
(klit
9
o-ris; “hill”),
a small, protruding structure composed largely of erectile tissue,
which is homologous to the penis of the male. Its exposed por-
tion is called the
glans of the clitoris
. It is hooded by a skin fold
called the
prepuce of the clitoris
, formed by the junction of the
labia minora folds.
Te clitoris is richly innervated with sensory nerve endings
sensitive to touch. It becomes swollen with blood and erect dur-
ing tactile stimulation, contributing to a female’s sexual arousal.
Like the penis, the
body of the clitoris
has dorsal erectile col-
umns (corpora cavernosa) attached proximally by crura, but it
lacks a corpus spongiosum that conveys a urethra.
In males the urethra carries both urine and semen and runs
through the penis, but the female urinary and reproductive
tracts are completely separate. Instead, the
bulbs of the ves-
tibule
(Figure 27.16b), which lie along each side of the vagi-
nal orifice and deep to the bulbospongiosus muscles, are the
homologues of the single penile bulb and corpus spongiosum
of the male. During sexual stimulation the bulbs of the vestibule
engorge with blood. Tis may help the vagina grip the penis and
also squeezes the urethral orifice shut, which prevents semen
(and bacteria) from traveling superiorly into the bladder during
intercourse.
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