The ovary is a firm, almond-shaped organ measuring about
3.5 cm long by 2 cm wide and 1 cm thick and attached to the back of the broad
ligament by the mesovarium through which blood vessels pass to enter the hilum.
It is attached to the pelvic wall by the suspensory ligament and the uterus
by the ovarian ligament. In the nulliparous woman, the organ usually lies
against the lateral pelvic wall. During pregnancy, the enlarging uterus pulls
the ovary up into the abdominal cavity. After childbirth, when the broad ligament
is lax, the ovary becomes quite mobile and its position then becomes variable.
The ovary is covered by a thin fibrous capsule, the tunica
albuginea, and is smooth until puberty. Thereafter the surface becomes progressively
scarred by degenerating corpora lutea making it irregular. After the menopause
it becomes shrunken and its surface pitted with scars.
The ovary is covered by a low cuboidal epithelium, called
the germinal epithelium (because it was wrongly thought to be the origin
of oocytes). Beneath this epithelium is the tunica albuginea, which
consists of collagen fibers and covers the outer zone, called the cortex.
The cortex is highly cellular and contains follicles and corpora
lutea and albicantia. This zone merges with the inner medulla
without a clearly defined demarcation line. The medulla is smaller and contains
loose connective tissue, occasional smooth muscle cells and numerous, tortuous
arteries and veins.
The cortex contains spindle, fibroblast-like cells which
give rise to the granulosa and theca cells, which are steroid producing cells
and surround the germ cells to form primordial follicles. At birth, these
are the only type of follicles present. After birth, a few primordial follicles
at a time undergo further development to form primary follicles. After puberty,
during each menstrual cycle several primary follicles begin to grow rapidly
into secondary follicles but one, the dominant follicle develops faster
than the rest to form the graafian follicle, which ruptures at ovulation.
The other secondary follicles undergo follicular atresia. After ovulation
the granulosa cells become luteinized and the follicle becomes the bright
yellow corpus luteum. If fertilization and implantation fail to occur, the
corpus luteum involutes, becomes white and forms the corpus albicans.
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