Second Week: Becoming Implanted and Bilaminar Flashcards
what does the blastocyst do on days 4-5 to prepare for implantation?
-enters uterine cavity
-hatches from the zona pellucida to interact directly with the endometrium
On days 4-5, how does the endometrium prepare for implantation?
is in secretory phase starting to thicken and accumulate nutrients to provide suitable cellular and nutritional environment
describe what takes place for decidual reaction throughout the endometrium
-spiral arteries grow rapidly and closer to surface
-glands accumulate glycogen and become coiled
endometrial stroma cells accumulate nutrients, lipids, and glycogen and become ____________________
decidual cells
highly vascularized endometrium is thus called the ___________
decidua
when does implantation begin?
day 6
what happens during stage 1 of implantation?
blastocyst attaches to endometrium
-usually on the posterior wall of uterus
-at the embryonic pole of blastocyst
what happens during stage 2 of implantation?
penetration of the endometrial epithelium
-endometrium induces trophoblast differentiation into cytotrophoblast and syncytiotrophoblast
is the cytotrophoblast the inner or outer layer?
inner
syncytiotrophoblast
forms the outer layer; multiple cells coalesce to form large multinucleated cells
what happens during the final stage of implantation? (Day 12)
invasion of endometrial stroma
-cytotrophoblast produces proteolytic enzymes to break down extracellular matrix
-syncytiotrophoblast penetrates endometrium with finger-like projections and cavities (lacunae) form
what is secreted during the final stage of implantation that maintains the corpus luteium?
human chorionic gonadotropin (hCG)
describe the uteroplacental circulatory system
trophoblastic lacunae coalesce and anastomose with expanded maternal capillaries (sinusoids)
what are the two layers of the embryoblast?
-epiblast (primitive ectoderm): amniotic cavity
-hypoblast (primitive endoderm): blastocyst cavity–> primary yolk sac
migrating cells from the hypoblast on day 8 convert the blastocyst cavity into the ______________________
primary yolk sac
The epiblast gives rise to the amniotic cavity on its ___________ aspect.
dorsal
what lines the roof of the amniotic cavity?
amnioblasts
On day 10 the hypoblast and primary yolk sack produce cells that form the________________________
extraembryonic mesoderm
extraembryonic mesoderm takes up residence and separates what?
separates the cytotrophoblast from the yolk sack and amniotic cavity
on day 12, small cavities (lacunae) form in the extraembryonic mesoderm which splits it and forms the _____________________________
chorionic cavity
how is the definitive (secondary) yolk sac formed?
on day 12-13, a second wave of migration of cells from the hypoblast displaces the primary yolk sac
what are the important functions of the secondary yolk sac for the first 4 weeks?
-blood cell production (hematopoiesis)
-primordial germ cells
-nutrition
connecting stalk
-where the embryo remains tethered to the cytotrophoblast on day 14
-later becomes the umbilical cord
extraembryonic splanchnic mesoderm
mesoderm layer associated with the yolk sac
extraembryonic somatic mesoderm
mesoderm layer associated with the amnion and cytotrophoblast
what does the primary villi consist of?
-cytotrophoblast core
-penetrating syncytiotrophoblast column
what does the secondary villi consist of?
-extraembryonic mesoderm
-cytotrophoblast
-syncytiotrophoblast
what happens for formation of tertiary villus
the extraembryonic mesodermal core differentiates into blood vessels
development is regulated by maternal genes
inner cell mass/embryoblast
placental development is regulated by paternal genes
outer cell mass/trophoblast
imprinted genes
the allele from the parent that is suppressed by methylation of the DNA
what does the genetic conflict hypothesis done by analysis of hydatidiform moles show?
-paternal genes promote placenta development to provide maximal resources for his offspring
-maternal genes promote embryo development favoring conservation of resources (for mother and future offspring)
what is a hydatidiform mole and how is it an example of parental gene imprinting?
-proliferation of trophoblastic/placental tissue with swelling of villi
-enlarged uterus with cystic mass (no embryo)
-stimulates pregnancy
-abnormally high HCG levels
-vaginal bleeding, pelvic pain, vomiting
what are the 2 imprinting disorders involving chromosome 15?
-prader-willi syndrome
-angelman syndrome
prader-willi syndrome
-extreme feeding behavior, hypogonadism, mild mental disability
-mutation inherited from father
-maternal genes are imprinted
angelman syndrome
-developmental delays, speech and balance, seizures, happy demeanor
-mutation inherited from mother
-paternal genes are imprinted
what is X inactivation and its purpose?
-one of the X chromosomes in females is inactivated and becomes a condensed Barr body
-it compensates for the presence of two X chromosomes in the female to ensure that she doesn’t have twice as many X chromosome gene products
what percentage of X chromosomes are inactivated in adult female
about 50% paternal and 50% maternal
what is the clinical correlation of X inactivation
it affects the inheritance of certain genetic diseases
describe Duchenne muscular dystrophy
-x linked recessive: X inactivation
-female is silent carrier bc there’s enough healthy x chromosomes to compensate for diseased
-symptoms appear before age 5
what are the symptoms of Duchenne muscular dystrophy
-progressive muscle wasting and weakness, muscle fibers degenerate and replaced by fat and connective tissue
-breathing difficulties by age 20
what is the specific mutation in Duchenne muscular dytrophy
mutation of gene for dystrophin
