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Ch. 3: Formation of the Bilaminar Embryonic Disc: 2nd Week
LECOM Yr 1
21
Medical
Graduate
10/15/2011

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Cards

Term
implantation of the blastocyst occurs during which week of development?
Definition
2nd week
Term
where does the syncytiotrophoblast invade?
Definition
invades the endometrial connective tissue and the blastocyst slowly embeds itself in the endometrium

displace endometrial cells which then undergo apoptosis which facilitates the invasion
Term
what hormone does the syncytiotrophoblast produce?
Definition
human chorionic gonadotrophin (hCG)- enters the maternal blood via lacunae
Term
what is the corpus luteum?
Definition
an endocrine glandular structure that secretes estrogen and progesterone to maintain the pregnancy
Term
what is the amnion?
Definition
composed of amniogenic cells (amnioblasts) which separate from the epiblast and enclose the amniotic cavity
Term
what are the 2 layers of the embryonic disc?
Definition
the epiblast and the hypoblast

epiblast- the thicker layer, consisting of high columnar cells related to the amniotic cavity

hypoblast- consisting of small cuboidal cells adjacent to the exocoelomic cavity
Term
what forms the roof and the floor of the amniotic cavity?
Definition
the epiblast forms the floor of the amniotic cavity and is continuous peripherally with the amnion

the hypoblast forms the roof of the exocoelomic cavity and is continuous with the thin exocoelomic membrane
Term
the fluid in the lacunar spaces is termed what?
Definition
embryotroph

passes to the embryonic disc by diffusion and provides nutritive material to the embryo
Term
oxygenated blood passes into the lacunae from _____ arteries and poorly oxygenated blood is removed from them through the _______ veins.
Definition
spiral endometrial arteries; endometrial veins
Term
true or false: the 10 day human conceptus is completely embedded in the endometrium
Definition
true
Term
what is the decidual reaction and what is its function?
Definition
as the conceptus implants, the endometrial connective tissue cells undergo a transformation, the decidual reaction.

after the cells swell because of the accumulation of glycogen and lipid in their cytoplasm, they are known as decidual cells

function is to provide nutrition for the early embryo and an immunologically privileged site for the conceptus
Term
what characterizes the end of the second week?
Definition
the appearance of primary chorionic villi
Term
what is the chorion and what does it form?
Definition
the extraembryonic somatic mesoderm and the two layers of the trophoblast form the chorion

the chorion forms the wall of the chorionic sac, within which the embryo and its amniotic sac and umbilical vesicle are suspended by the connecting stalk
Term
the extraembryonic coelom splits the extraembryonic mesoderm into what 2 layers?
Definition
extraembryonic somatic mesoderm- lining the trophoblast and covering the amnion

extraembryonic splanchnic mesoderm- surrounding the umbilical vesicle
Term
what is transvaginal ultrasonography used for measuring?
Definition
the chorionic (gestational) sac diameter

valuable for evaluating early embryonic development and pregnancy outcome
Term
describe the structure of the 14 day embryo
Definition
still has the form of a flat bilaminar embryonic disc but the hypoblastic cells in a localized area are now columnar and form a thickened circular area- the prechordal plate which indicates the future site of the mouth and an important organizer of the head region
Term
where does implantation of the blastocyst usually occur?
Definition
in the endometrium of the uterus, superior in the body of the uterus, slightly more often on the posterior than on the anterior wall
Term
95%-98% of ectopic pregnancies occur where?
Definition
in the uterine tubes, most often in the ampulla and isthmus

ectopic pregnancy is approx. 2% of all pregnancies
Term
when does implantation of the blastocyst begin and when does it end?
Definition
begins at the end of the first week and is completed by the end of the second week
Term
what is placenta previa?
Definition
a placenta that partially or completely covers the internal os

may cause bleeding because of premature separation of the placenta during pregnancy or at delivery of the fetus
Term
more than 50% of all known spontaneous abortions results from what?
Definition
chromosomal abnormalities
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