accessory organs include both internal and external
reproductive organs (fig. 1-61).
The ovaries, as stated earlier, are the primary
female reproductive organs, producing the female sex
cells and sex hormones (fig. 1-61).
The ovaries, or female gonads, are two
almond-shaped glands suspended by ligaments in the
upper pelvic cavity. There is one ovary on each side of
the uterus. The ligaments that suspend the ovaries
contain ovarian blood vessels and nerves.
The tissues of an ovary are divided into two
regions, an inner medulla and an outer cortex. The
ovarian medulla is largely composed of loose
connective tissue, numerous blood vessels, lymph
vessels, and nerves. The ovarian cortex is composed of
compact tissue containing tiny masses of cells called
ovarian (primordial) follicles. The follicles contain
the female sex cells or ova. The external surface of the
ovary is covered by a layer of cuboidal epithelium
cells. Beneath the epithelium is a layer of dense
In the outer region of the ovarian cortex,
microscopic groups of cells are referred to as
primordial follicles. The primordial follicles consist of
a single large cell, called an oocyte, which is
surrounded by a layer of flattened epithelial cells
called follicular cells. The oocyte is an immature egg
cell. Follicular cells surround a developing egg cell
and secrete female sex hormones. There are
approximately 400,000 primordial follicles at puberty.
Of these, probably fewer than 500 will be released
from the ovary during the reproductive life of a female.
At puberty, the anterior pituitary gland secretes
increased amounts of FSH (follicle-stimulating
hormone). In response, the ovaries enlarge and many
of the primordial follicles begin to mature. During this
maturation process, the oocyte enlarges and the follicle
cells multiply until there are 6 to 12 layers. Fluid-filled
spaces begin to appear among the follicle cells. These
spaces join to form a single cavity called the antrum.
Ten to fourteen days after this process begins, the
primordial follicle reaches maturity. The mature
primordial follicle (preovulatory or graafian follicle)
and its fluid-filled cavity bulges outward on the surface
of the ovary, like a blister.
Ovulation is the process by which the mature
oocyte is released from the primordial follicle (fig.
1-62). Ovulation is stimulated by hormones from the
anterior pituitary gland. These hormones cause the
mature follicle to swell rapidly and its walls to weaken.
Eventually the wall ruptures, permitting the oocyte and
1 or 2 layers of follicle cells to be released from the
After ovulation, the oocyte is usually propelled to
the opening of a nearby fallopian tube. If the oocyte is
not fertilized by a sperm cell within a relatively short
time, it will degenerate.
This process of ovulation occurs once a month.
Each ovary normally releases an ovum every 56 days.
The right and left ovary alternately discharge an ovum
approximately every 28 days. The menstrual cycle in
most women is therefore approximately 28 days.
Female Sex Hormones
Female sex hormones are produced by the ovaries
and various other tissues, such as the adrenal glands,
pituitary gland, and placenta (during pregnancy).
These female sex hormones are estrogen and
The primary source for estrogen is the ovaries. At
puberty, estrogen stimulates enlargement of various
accessory organs, which include the vagina, uterus,
fallopian tubes, and external structures. Estrogen is
also responsible for the development and maintenance
Figure 1-61.The female reproductive system.