464 Chapter 19
Primary follicle (^)
(oocyte) Zone pellucida (^)
Mesovarium
Connective tissue (^)
Corpus albicans (^)
Mature corpus luteum (^)
Early corpus luteum (^)
Blood clot^ Stroma of^
cortex (^)
Secondary follicle
Tunica albuginea
Germinal epithelium
Follicular fluid
Graafian follicle
(mature follicle)
Stroma of medulla
Corpus hemorrhagicum
(ruptured follicle)
Discharged ovum
(^) ®
Learning
Cengage ©
Figure 19- 7 A microscopic view of an individual ovary and its internal anatomy.
gland that begins to secrete estrogen and is ready to eject the
mature egg, an event known as ovulation. After the egg
ruptures from the mature graafian follicle, the follicle changes
into the corpus luteum (KOR-pus LOO-tee-um), or yellow
body, which produces estrogen and progester-one and
eventually degenerates to become the corpus al-bicans
( KOR-pus AL-bih-konz) or white body.
The functions of the ovaries are to produce eggs or
ova, discharge the ova in ovulation, and secrete the female
sex hormones estrogen and progesterone. The rest of the
female system consists of ducts that transport and nurture
the egg and, if fertilization occurs, delivers the fetus to the
outside world during birth. The duct system consists of the
uterine or fallopian tubes, the uterus, and the vagina.
Oogenesis (oh-oh-JEN-eh-sis) or formation of the
fe-male sex cells or eggs occurs in the ovaries (Figure 19-
8). In males, the process is called spermatogenesis and oc-
curs in the seminiferous convoluted tubules of the tes-tes.
In males, the process begins in the fetus, continues at
puberty, and men can produce sperm throughout their lives.
In women, the process begins in the fetus, contin-ues at
puberty, but ends at menopause around the age of 50. In
addition, the total number of eggs that a woman can
produce and release is determined at birth.
In a developing female fetus, the female stem cells called
oogonia (oh-oh-GO-nee-ah) divide by mitosis to produce
primary oocytes (PRYE-mary oh-oh-sightz). They become
surrounded by follicular cells in the ovary and are now part of
the primary follicles. Around 700,000 are
produced at this time and represent the total number of eggs
that a female could produce during her reproductive years.
They now await further development until puberty.
At puberty, the ovarian cycle is stimulated when the
anterior pituitary gland secretes follicle-stimulating hor-
mone (FSH). Only a small number of primary follicles will
grow and develop, with only one egg being released each
month. Only about 450 eggs will be produced from the
store of 700,000 primary oocytes through the process of
meiosis.
After the first meiotic division, the primary oocyte
becomes two cells. The secondary oocyte is the larger
of the two cells; a very small cell called the polar body is
non-functional. During the second meiotic division, which
occurs only after fertilization, the secondary oocyte and the
polar body divide again and the secondary oocyte be-comes
an ootid (OH-oh-tid), or mature egg cell, and due to
unequal division of the cytoplasm another polar body is
formed. The first polar body from the first meiotic di-vision
again divides in the second meiotic division to be-come
two nonfunctional polar bodies. After the second meiotic
division, one functional egg cell is produced and three
nonfunctional polar bodies. This is very different from
meiosis in men, in whom four functional sperm cells are
produced. However, the sperm cells are very tiny with few
stored nutrients and will not survive very long be-cause
they must get their nutrients from the seminal fluid. The
egg cell, however, has lots of stored food because it is a
large cell and can supply the developing embryo until it
embeds itself in the endometrial lining of the uterus.