382
UNIT 3
Organ Systems
D.Cui
Morula
Zona
pellucida
Blastomeres
(subdivided zygote)
Trophoblast
Cytotrophoblast
Blastocyst
cavity
(blastocoel)
Inner cell
mass
(embryoblast)
Syncytiotrophoblast
Bilaminal
embryonic disc
Blastocyst
Implantation
Blastocyst
cavity
Amniotic
cavity
Implantation
site
Uterine
Uterine
glands
glands
Uterine
glands
Endometrium
A
Figure 19-11A.
Implantation, endometrium of the uterus.
H&E,
3
8
After an ovum has been successfully fertilized by a spermatozoan in the ampulla of the oviduct, the
zygote
(fertilized oocyte)
undergoes mitotic cell division (
cleavage
) and becomes a multicellular structure called the
morula
. The morula develops into the
blastocyst
, which is transported into the uterus. The process of the
blastocyst
attaching to the endometrium of the uterus is called
implantation
. Implantation occurs at the end of the secretory phase; the endometrium during this period of time is also called the
premenstrual endometrium
(days 25–28). Implantation usually occurs on the posterior wall of the body of the uterus. If implanta-
tion succeeds, the trophoblast differentiates into two cell layers: an inner
cytotrophoblast layer
and an outer
syncytiotrophoblast
layer
. The
syncytiotrophoblast
attaches to and invades the endometrium of the uterus, and the process of placentation begins.
hCG
secreted by the placenta stimulates the
corpus luteum
to remain active and continue to secrete
estrogen
and
progesterone
during the
pregnancy. The photomicrograph on the
left
shows an implantation site enclosed within the connective tissue of the endometrium.
CLINICAL CORRELATIONS
Figure 19-11B.
Endometrial Adenocarcinoma.
H&E,
3
48
Endometrial adenocarcinoma
is the most common form of endometrial
cancer, accounting for approximately 80% of cases. The majority of cases
of endometrial adenocarcinoma arise in the setting of elevated levels of
estrogen
unopposed by the action of
progesterone
, causing
endometrial
hyperplasia
. Some cases, however, arise in postmenopausal women with
atrophy of the endometrium. Excess or unopposed estrogen may be due
to
chronic anovulation, obesity, ovarian granulosa cell tumors, or exogenous
hormone intake. In the early stage, the cancer is usually asymptomatic.
Common symptoms include vaginal bleeding,
menorrhagia
,
metrorrhagia
,
and lower abdominal pain. Histologically, the cancer is characterized by
the presence of cells resembling the glandular cells of the endometrium,
and range from well differentiated with gland formation to poorly differ-
entiated with solid sheets of
neoplastic cells
. Endometrial biopsy is widely
used in the diagnosis of the cancer. Treatment options include surgical
removal of the uterus, radiation therapy, and chemotherapy.
Figure 19-11C.
Uterine Leiomyoma.
H&E,
3
95
Uterine leiomyoma
, or
± broid
, is a benign neoplasm, derived from smooth
muscle cells of the uterine myometrium. Leiomyomas represent the most
common benign neoplasm in women, and occur more frequently in
African
Americans. Leiomyomas occur in the reproductive years when estrogen levels
are high, and tend to regress during menopause. Most patients with F broids
are asymptomatic, but, as the tumor enlarges, symptoms may include abnor-
mal bleeding, menorrhagia, lower abdominal pain, and increased urinary
frequency. Grossly, leiomyomas are well circumscribed and may be in sub-
serosal, intramural, or submucosal locations. Leiomyomas can be single but
are often multiple and may become quite large. The cut surface is typically
white to tan, with a whorled, bulging appearance. Histologically, the tumor
cells appear as well- differentiated, spindle-shaped smooth muscle cells, often
with increased extracellular matrix, such as
collagen
,
proteoglycan
, and
± bronectin
. Leiomyomas rarely become their malignant counterpart,
leio-
myosarcomas
, which usually develop
de novo
. Treatment options include
hysterectomy
,
myomectomy
(removal of the F broid), and hormone therapy.
Adenocarcinoma
invading the
myometrium
B
Fascicles of
smooth
muscle
C
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