Second Week: Becoming Implanted and Bilaminar

Question 1

what does the blastocyst do on days 4-5 to prepare for implantation?

Answer 1

-enters uterine cavity
-hatches from the zona pellucida to interact directly with the endometrium

Question 2

On days 4-5, how does the endometrium prepare for implantation?

Answer 2

is in secretory phase starting to thicken and accumulate nutrients to provide suitable cellular and nutritional environment

Question 3

describe what takes place for decidual reaction throughout the endometrium

Answer 3

-spiral arteries grow rapidly and closer to surface
-glands accumulate glycogen and become coiled

Question 4

endometrial stroma cells accumulate nutrients, lipids, and glycogen and become ____________________

Answer 4

decidual cells

Question 5

highly vascularized endometrium is thus called the ___________

Answer 5

decidua

Question 6

when does implantation begin?

Answer 6

day 6

Question 7

what happens during stage 1 of implantation?

Answer 7

blastocyst attaches to endometrium
-usually on the posterior wall of uterus
-at the embryonic pole of blastocyst

Question 8

what happens during stage 2 of implantation?

Answer 8

penetration of the endometrial epithelium
-endometrium induces trophoblast differentiation into cytotrophoblast and syncytiotrophoblast

Question 9

is the cytotrophoblast the inner or outer layer?

Answer 9

inner

Question 10

syncytiotrophoblast

Answer 10

forms the outer layer; multiple cells coalesce to form large multinucleated cells

Question 11

what happens during the final stage of implantation? (Day 12)

Answer 11

invasion of endometrial stroma
-cytotrophoblast produces proteolytic enzymes to break down extracellular matrix
-syncytiotrophoblast penetrates endometrium with finger-like projections and cavities (lacunae) form

Question 12

what is secreted during the final stage of implantation that maintains the corpus luteium?

Answer 12

human chorionic gonadotropin (hCG)

Question 13

describe the uteroplacental circulatory system

Answer 13

trophoblastic lacunae coalesce and anastomose with expanded maternal capillaries (sinusoids)

Question 14

what are the two layers of the embryoblast?

Answer 14

-epiblast (primitive ectoderm): amniotic cavity
-hypoblast (primitive endoderm): blastocyst cavity–> primary yolk sac

Question 15

migrating cells from the hypoblast on day 8 convert the blastocyst cavity into the ______________________

Answer 15

primary yolk sac

Question 16

The epiblast gives rise to the amniotic cavity on its ___________ aspect.

Answer 16

dorsal

Question 17

what lines the roof of the amniotic cavity?

Answer 17

amnioblasts

Question 18

On day 10 the hypoblast and primary yolk sack produce cells that form the________________________

Answer 18

extraembryonic mesoderm

Question 19

extraembryonic mesoderm takes up residence and separates what?

Answer 19

separates the cytotrophoblast from the yolk sack and amniotic cavity

Question 20

on day 12, small cavities (lacunae) form in the extraembryonic mesoderm which splits it and forms the _____________________________

Answer 20

chorionic cavity

Question 21

how is the definitive (secondary) yolk sac formed?

Answer 21

on day 12-13, a second wave of migration of cells from the hypoblast displaces the primary yolk sac

Question 22

what are the important functions of the secondary yolk sac for the first 4 weeks?

Answer 22

-blood cell production (hematopoiesis)
-primordial germ cells
-nutrition

Question 23

connecting stalk

Answer 23

-where the embryo remains tethered to the cytotrophoblast on day 14
-later becomes the umbilical cord

Question 24

extraembryonic splanchnic mesoderm

Answer 24

mesoderm layer associated with the yolk sac

Question 25

extraembryonic somatic mesoderm

Answer 25

mesoderm layer associated with the amnion and cytotrophoblast

Question 26

what does the primary villi consist of?

Answer 26

-cytotrophoblast core
-penetrating syncytiotrophoblast column

Question 27

what does the secondary villi consist of?

Answer 27

-extraembryonic mesoderm
-cytotrophoblast
-syncytiotrophoblast

Question 28

what happens for formation of tertiary villus

Answer 28

the extraembryonic mesodermal core differentiates into blood vessels

Question 29

development is regulated by maternal genes

Answer 29

inner cell mass/embryoblast

Question 30

placental development is regulated by paternal genes

Answer 30

outer cell mass/trophoblast

Question 31

imprinted genes

Answer 31

the allele from the parent that is suppressed by methylation of the DNA

Question 32

what does the genetic conflict hypothesis done by analysis of hydatidiform moles show?

Answer 32

-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)

Question 33

what is a hydatidiform mole and how is it an example of parental gene imprinting?

Answer 33

-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

Question 34

what are the 2 imprinting disorders involving chromosome 15?

Answer 34

-prader-willi syndrome
-angelman syndrome

Question 35

prader-willi syndrome

Answer 35

-extreme feeding behavior, hypogonadism, mild mental disability
-mutation inherited from father
-maternal genes are imprinted

Question 36

angelman syndrome

Answer 36

-developmental delays, speech and balance, seizures, happy demeanor
-mutation inherited from mother
-paternal genes are imprinted

Question 37

what is X inactivation and its purpose?

Answer 37

-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

Question 38

what percentage of X chromosomes are inactivated in adult female

Answer 38

about 50% paternal and 50% maternal

Question 39

what is the clinical correlation of X inactivation

Answer 39

it affects the inheritance of certain genetic diseases

Question 40

describe Duchenne muscular dystrophy

Answer 40

-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

Question 41

what are the symptoms of Duchenne muscular dystrophy

Answer 41

-progressive muscle wasting and weakness, muscle fibers degenerate and replaced by fat and connective tissue
-breathing difficulties by age 20

Question 42

what is the specific mutation in Duchenne muscular dytrophy

Answer 42

mutation of gene for dystrophin