2. UTERUS, UTERINE TUBES, AND OVARIES
The body of the uterus narrows from the fundus, the rounded, superior part of
the body, to the isthmus, constricted region between the body and cervix.
The cervix of the uterus is its tapered vaginal end that is nearly cylindrical in
shape.
The lumen of the cervix, the cervical canal, has a constricted opening at each end.
The internal os communicates with the cavity of the uterine body and the external
os communicates with the vagina.
Uterus The uterus
a thick-walled, pear-shaped muscular
organ
The uterus consists of two major parts:
Body, the expanded superior two thirds
Cervix, the cylindrical inferior one third
3. UTERUS, UTERINE TUBES, AND
OVARIES
The walls of the body of the uterus
consist of three layers
Perimetrium, the thin external layer
Myometrium, the thick smooth muscle
layer
Endometrium, the thin internal layer
The perimetrium is a peritoneal layer
that is firmly attached to the
myometrium.
During the luteal (secretory) phase of the
menstrual cycle, three layers of the
endometrium can be distinguished
microscopically (see Fig. C)
A thin, compact layer consisting of
densely packed, connective tissue around
the necks of the uterine glands
A thick, spongy layer composed of
edematous connective tissue containing
the dilated, tortuous bodies of the uterine
glands
A thin, basal layer containing the blind
4. During the luteal (secretory) phase of the
menstrual cycle, three layers of the
endometrium can be distinguished
microscopically (see Fig. C)
A thin, compact layer consisting of densely
packed, connective tissue around the necks of
the uterine glands
A thick, spongy layer composed of
edematous connective tissue containing the
dilated, tortuous bodies of the uterine glands
A thin, basal layer containing the blind ends
of the uterine glands
The walls of the body of the
uterus consist of three layers
Perimetrium, the thin external
layer
Myometrium, the thick smooth
muscle layer
Endometrium, the thin internal
layer
The perimetrium is a
peritoneal layer that is firmly
attached to the myometrium.
5. About the sixth day, the blastocyst implants by
attaching itself to the uterine epithelium
The uterus consists of three layers, endometrium, the
mucosal lining, myometrium, thick layer of
smooth muscles and perimetrium, the peritoneal
covering of the outside wall.
During the ovarian cycle the endometrium passes
through the follicular or proliferative phase,
secretory or progestational phase and the
menstrual phase.
6. UTERUS, UTERINE TUBES, AND
OVARIES
At the peak of its development,
the endometrium is 4 to 5 mm
thick.
The basal layer of the
endometrium has its own blood
supply and is not sloughed off
during menstruation.
The compact and spongy layers,
known collectively as the
functional layer, disintegrate
and are shed during
menstruation and after
parturition (delivery of a baby).
7. Proliferation phase:
It begins at the end of the menstrual phase under the
influence of estrogen.
Secretory phase:
This phase begins 2-3 days after ovulation in response to
progesterone produced by the corpus luteum. Implantation
occurs during this phase. During this period three layers of
the uterine mucosa can be distinguished (superficial
compact layer, intermediate compact layer and a thin
basal layer).
Menstrual phase:
If fertilization does not occur the shedding of compact and
spongy layer begins, making the initiation of the menstrual
phase.
10. 2nd week of development
After implantation, over the next several
days, the blastocyst invades this tissue.
By this time, the trophoblast has
differentiated into two layers: an invasive
outer multinucleated cytoplasmic mass
called the syncytiotrophoblast, and an inner
proliferative, the cytotrophoblast.
SYNCYTIOTROPHOBLAST
CYTOTROPHOBLAST
11.
12.
13. The embryoblast reorganizes into two layers, the
epiblast dorsally and the hypoblast ventrally
EPIBLAST DORSALLY
HYPOBLAST VENTRALLY
14. Two cavities are formed, the amniotic cavity dorsal to the epiblast and the
yolk sac cavity ventral to the hypoblast
AMNIOTIC
CAVITY
AND THE
YOLK SAC
CAVITY
15. The epiblast and hypoblast appear as a slightly elongated disc (the
bilaminar germ disc) and it is the epiblast that will give rise to all of the
tissues of the embryo.
16. Proliferation of epiblast
cells at the margins of
the disc forms
amnioblasts that line
the amniotic cavity.
In a similar fashion, a
primitive yolk sac is
created by proliferation
of hypoblast cells at the
disc margins.
Thus, the embryonic disc is
suspended between
these two cavities.
17. Two layers of
extraembryonic
mesoderm are
formed between
the embryo and
its cavities and
cytotrophoblast.
Extraembryonic mesoderm is formed by the cells derived from the yolk sac and forms a connective
tissue network.
Initially, this tissue forms as a single layer, but it soon separates into two layers: a layer around the
yolk sac, which is the extraembryonic splanchnic mesoderm, and a layer over the amnion and on
the inner surface of the cytotrophoblast, which is the extraembryonic somatic mesoderm.
18. By 12 to 14 days, cells of
the syncytiotrophoblast
erode uterine blood
vessels, and maternal
blood fills spaces
(lacunae) that form in the
syncytium, bringing
nutrients closer to the
developing embryo.
19.
20. 3rd week of development
Gastrulation which results in the
development of three germ layers,
ectoderm, endoderm and mesoderm,
occurs during this week.
21. 3rd week of
development
Gastrulation begins
with the formation of a
primitive streak, which
later appears as a
narrow groove, on the
surface of the epiblast.
22. 3rd week of
development
The cephalic end of the
primitive streak is called
primitive node.
The primitive node
consists of a slightly
elevated area surrounding
the small primitive pit.
23. 3rd week of development
Cells of the epiblast migrate toward the primitive streak.
Upon arrival at the primitive streak they become flask
shaped and detach from the epiblast and lie beneath it.
This type of cell movement is called invagination.
24. 3rd week of development
Some of the invaginating cells displaces the hypoblast,
giving rise to endoderm.
Some of the other cells occupy the region between the
newly formed endoderm and the epiblast forming the
mesoderm.
The cells remaining in the epiblst forms the ectoderm.
