Human Physiology, 14th edition (2016)

Reproduction 723

released from the ovary. The empty follicle then becomes a

corpus luteum, which ultimately degenerates at the end of a

nonfertile cycle.

LEARNING OUTCOMES

After studying this section, you should be able to:

8. Describe the stages of oogenesis, and the different
   ovarian follicles.


9. Describe ovulation and the formation of a corpus
   luteum.

The two ovaries ( fig. 20.23 ), about the size and shape of large
almonds, are suspended by means of ligaments from the pelvic
girdle. Extensions called fimbriae of the uterine (fallopian)
tubes partially cover each ovary. Ova that are released from the
ovary—in a process called ovulation —are normally drawn into
the uterine tubes by the action of cilia on the epithelial lining
of the tubes. The lumen of each uterine tube is continuous with
the uterus (or womb), a pear-shaped muscular organ held in
place within the pelvic cavity by ligaments.
The uterus consists of three layers. The outer layer of con-
nective tissue is the perimetrium, the middle layer of smooth
muscle is the myometrium, and the inner epithelial layer is
the endometrium. The endometrium is a stratified, squamous,
nonkeratinized epithelium that consists of a stratum basale and
a more superficial stratum functionale. The stratum functio-
nale, which cyclically grows thicker as a result of estrogen and
progesterone stimulation, is shed at menstruation.

Infundibulum

of uterine tube

Fimbriae

Egg cell

Endometrium Follicle

Myometrium

Perimetrium

Fornix of vagina

Cervix of uterus

Vagina

Uterine tube

Ampulla

of uterine

tube

Body of uterus

Fundus of uterus

Ovarian ligament

Ovary

Mesovarium

Suspensory
ligament of
ovary

Round
ligament

Broad
ligament
of uterus

Figure 20.23 The uterus, uterine tubes,

and ovaries. The supporting ligaments can also

be seen in this posterior view.

CLINICAL APPLICATION

Uterine fibroids ( leiomyomas ) are benign tumors that arise in

the uterine smooth muscle (myometrium) and are composed

of smooth muscle cells and an extracellular matrix. Their

growth is stimulated by estradiol and progesterone, and they

may extend into the uterine cavity or into the peritoneal cavity.

Fibroids as small as 10 mm or as large as 20 cm can pro-

duce such symptoms as profuse menstrual bleeding, loss of

pregnancy, urinary incontinence, and pelvic discomfort. They

are extremely common; 70% to 80% of women have at least

one fibroid by the age of 50. Various surgical interventions are

available, including hysterectomy; indeed, the majority of hys-

terectomies are performed because of uterine fibroids.

Clinical Investigation CLUES

Linda was told that she might have fibroids, but that they

probably were not responsible for her symptoms.

• What are uterine fibroids, and why might the doctor
  have told her that she could have them?


• What are the symptoms of uterine fibroids?

The uterus narrows to form the cervix ( 5  neck), which opens

to the tubular vagina. The only physical barrier between the vagina

and uterus is a plug of cervical mucus. These structures—the

vagina, uterus, and fallopian tubes—constitute the accessory sex