Primoridal follicles are present prepartum and either become atritic or develop
into primary follicles at puberty. The latter consist of a layer of squamous
to cuboidal cells surrounding a primary oocyte.
Continued development of a primary follicle produces a secondary follicle which
involves stratification of the follicular cells to form a stratum granulosum.
A prominent basement membrane separates the granulosum from the connective tissue
internal and external thecal layers.
A cavity, the antrum, develops within the granulosum and secretes liquor folliculi
consisting of the femal sex hormone estrogen as well as other growth factors
that promote ovulation, thicken the lining of the uterus, and cause growth of
ductal cells in the mammary gland.
Continued growth and the completion of meiosis 1 result in a mature, (Graafian)
preovulatory follcicle.
Detailed observation of a mature follicle shows a distinct primary egg membrane,
the zona pellucida, probably produced by both granulosum cells with a nutritive
role. It will adhere to this membrane after ovulation as the corona radiata.
The oocyte with its covering corona and the isthmus of granulosum cells that
join it to the remainder of the granulosum of the follicle are known as the
cumulus oophorus or discus proligerous.
The theca interna is thought to be secretory, probably producing androgens (male
sex hormones). These are likely converted to estrogens by the granulosum cells,
causing an increase in the amount of liquor folliculli which bulges the follicle
to the surface of the ovary just prior to ovulation.
The infant ovary illustrates the large number of primordial follicles that are present prepartum in mammalian females. In contrast to the male, whose gonial cells divide mitotically from puberty until death, the final number of gonial cells (up to 400,000) has been achieved during fetal life in the female. Most will become atritic and never ovulate.
After the thecal layers and the ovarian wall rupture at ovulation, the secondary
oocyte, surrounded by the zona pellucida and corona radiata, is released into
the peritoneal cavity. Peristalsis of the smooth musculature of the infundibulum
of the fimbriated end of the oviduct aids in captuing the oocyte and moving
it further down the oviduct. The liquor folliculi also spills into the peritoneal
cavity leaving behind a follicle, empty except for granulosum and thecal cells.
The granulsosum cells divide rapidly filling the former follicle with highly
folded endocrine tissue which constitutes the corpus luteum. Cells from the
theca interna become glandular in nature and contribute to the formation of
the corpus luteum. This "yellow body" secretes progesterone and estrogen,
which cause secretion and glandular elaboration in the lining of the uterus.
Ductal tissue of the mammary gland is also stimulated by these secretions.
The corpus luteum undergoes infiltration with connective tissue at the time
of menstruation or during the last week of pregnancy
The infiltration of connective into the degenerating corpus luteum changes the gland into an inactive white scar known as a corpus albicans (white body). This connective tissue has its origin in thecal cells. Most of these undergo some involution but some persist even in the senile (post menopausal) ovary. The remainder of the senile ovary is vascular connective tissue with no trace of follicles.
The infundibular portion of the oviduct (fallopian tube) terminates in many
elongated finger like processess called fimbria that adhere closely to the surface
of the ovary. The muscular layers contract during ovulation in peristalitic
fahsion and aid in capturing the oocyte and funneling it toward the uterus.
The oviduct is lined with ciliated and non-ciliated columnar epithelium. Cilia
beat toward the uterus and aid in moving the oocyute downward while non-ciliated
cells are likely secretory in nature.
Underlying the epithelium is a thin supporting connective tissue layer called
the lamina propria. This is underlayed by two layers of smooth muscle, an inner
circular and an outer longitudinal layer. An outer serous membrane, the serosa
covers the surface of the oviduct.
The infundibular portion of the oviduct is followed distally by the ampullar
region. Instead of fimbriae the lining of this portion of the oviduct is thrown
into longitudinal folds called plicae. The lining is a mixture of cilliated
and nonciliated columnar epithelium.
A thin lamina propria underlies the columnar epithelium. Inner circular and
outer longitudinal smooth muscle layers lie outside the lamina propria.
The oviduct is covered by a thin serosa. Isthmus and interstitial (intramural) regions lie distal to the ampulla and closely resemble it in structure.
The uterus arises as an embryological fusion of the two oviducts. Their muscular
layers are greatly increased in amount, and muscle fibers run in many directions.
This thick muscularis is the myometrium which experiences considerable growth
during pregnancy. The serosa or perimetrium covers part of the uterus.
The epithelium is of ciliated and non-ciliated simple columnar cells and is
referred to as the endometrium. These cells invaginate deeply into the stroma
of the endometrium forming glands whose secretion nourishes the newly implanted
embryo until a placenta develops.
The stroma is a mesenchyme like connective tissue which serves as a lamina propria.
The endometrium thickens during the menstrual cycle under the influence of ovarion
hormones and the glands deepen and become 'lacy'.
The endometrium is richly supported with spiral blood vessels in the inner layer
(stratum functionale) which become eschemic prior to menstruation to prevent
excessive blood loss. These distal arteries regenerate after mensturation.
The first phase of the endometiral cycle takes place as a result of the secretion
of estrogens from the developing follicle. This phase shows many mitoses in
the glands and stroma. Glands remain tubular rather than branched at this time.
This lasts until ovulation at midcycle. This tissue repair which culminates
in proliferation begins from the proximal part of the endometrium, the stratum
basale, which is never shed at menstruation. This phase is known as follicular,
proliferation, or hyperplasitic.
The proliferative phase begins at the end of menstruation. The basalis layer
of the endometrium is never shed and it is from this portion that regeneration
of stroma and surface epithelium glands begins.
An area referred to as the functionale, adjacent to the lumen, is the only part
of the endometrium which is shed.
The secretory, progravid or leuteal phase of the endometrium follows the proliferative
phase and is under control of the corpus luteum which secretes estrogen and
progesterone. Under the influence of these female steroid hormones the endometrium
thickens, the glands develop branches at right angles to their tubular protion
giving a lacy appearance. Secretion from glandular cells fills the lumen of
the gland. The outer part (functionale) of the endometrium imbibes water. Next,
new blood vessel growth occurs, making this area extremely succulent.
If fertilization does not occur the succulent endometrium undergoes a kind of
'clenching' of blood vessels. With a lack of blood vessels to the area, a condition
known as ischemia develops.
One or two days after hypoxia (ischemia) causes degeneration of the functionale, this portion of the endometrium is shed together with considerable amounts of blood and secretory product, resulting in the phenomenon of menstruation. While the basale remains intact the functionale presents a very degenerate, ragged appearance characteristic of the menstrual phase of the uterus. As the menstrual flow begins a new follicle commences development and the functionale soon begins repair leading to a new proliferative phase.
The uterus is said to be senile when its endometrium no longer undergoes cyclic
changes. Usually this occurs as the result of ovarian failure to produce follicles
and or, corpora lutea to stimulate the endometrium. Usually several corpora
albicans are evident in the senile uterus.
The lining is simple columnar with very few flands. The endometrium is thin
and the stroma component is most prominent. Gestation at this stage is impossible
and the woman is said to be menopausal.
The cervical region of the uterus shows the epithelium thrown into folds. Glands
are often large and branched. This portion of the uterus, which projects into
the vaginal vault does not undergo cyclic changes.
The cervical canal is the zone of juncture between the columnar epithelium of
the uterus and the stratified squamous epithelium of the vagina.
The cervix is rich in connective tissue but largly lacking muscularis layers.
The cervix has an epithelial lining of columnar cells. The bulk of this portion
of the organ is dense connective tissue of fibroblasts, collogen fibers, and
elastic fibers.
The glandular secretion from the cervix is largely mucous. During ovulation
this mucous becomes thin and increases in amount, an adaptation to aid sperm
in their journey to fertilize the oocyte.
The mucosa of the vagina is composed of a highly papillated, stratified squamous
epithelium underlayed by a thick connective tissue lamina propria. The wall
is thrown into folds called rugae. Papillae from the lamina propria are abundant.
A great deal of smooth muscular tissue is present.
The vagina is unique in that it contains no glands. Lubrication during sexual
activity comes from cervical glands or those embedded in the labia.