Human Physiology, 14th edition (2016)

724 Chapter 20

organs of the female ( fig.  20.24 ). Like the accessory sex organs
of the male, the female reproductive tract is affected by gonadal
steroid hormones. Cyclic changes in ovarian secretion, as will be
described in the next section, cause cyclic changes in the epithelial
lining of the tract.
The vaginal opening is located immediately posterior to
the opening of the urethra. Both openings are covered by longi-
tudinal folds—the inner labia minora and outer labia majora
( fig.  20.25 ). The clitoris, a small structure composed largely of
erectile tissue, is located at the anterior margin of the labia minora.

Ovarian Cycle

The germ cells that migrate into the ovaries during early embry-
onic development multiply, so that by about five months of
gestation (prenatal life) the ovaries contain approximately
6 million to 7 million oogonia. Most of these oogonia die prena-
tally through a process of apoptosis (chapter 3, section 3.5). The
remaining oogonia begin meiosis toward the end of gestation, at
which time they are called primary oocytes. Like spermatogen-
esis in the male, oogenesis is arrested at pro-phase I of the first
meiotic division and the primary oocytes are still diploid.

Fimbriae of

uterine tube

Posterior portion of

vaginal fornix

Cervix of uterus

Rectum

Vagina

Anus

Vaginal orifice

Labium majorum

Labium minorum

Clitoris

Urethra

Symphysis pubis

Urinary bladder

Uterus

Uterine tube

Ovary

Figure 20.24 The organs of the
female reproductive system. These are
shown in sagittal section.

Perineum Anus

Vaginal orifice

Urethral orifice

Labium majorum

Labium minorum

Hymen

Clitoris Mons pubis

Figure 20.25 The external female genitalia. The

labia majora and clitoris in a female are homologous to the

scrotum and penis, respectively, in a male.