topic 27 : mebryo II

Question 1

Amnion sac

Answer 1

-in 2nd week bilaminar discs forms with epi & hypoblasts
-from epiblast, amniotic cavity forms,
-epiblasts cell differentiate into amnioblast forms amnion
-amnion lines amnio cavity = amnion membrane
-as embryo develops cavity exapnds & fill with amniotic fluid

(at time t , amnio get in contact with choion (fusion of trophoblast & extraembryoic mebrane) & fuse
-making amniochoronic memebrane 1 of the memebranes surrounding fetus)

Question 2

Yolk sac

Answer 2

-develops from hypoblast layer
-as embryo grow, sac forms
-contributes to primitive gut dveelopment
-primary source of nurtrition
-produces first blood cells
-later placenta takes over & diminishes

Question 3

extraembryonic mesoderm

Answer 3

-extraembryonic coelom divides into
1.extra embryonis somatopleuric mesoderm: lines trophoblast & covers amnion
2.extraembryonic splanchnopleuric mesoderm : covers the yolk sac

chorion : extra. somatic mesoderm + cytotrophoblast + synciotrophoblast

within this membrane blood vessels begin to form

Question 4

placenta

Answer 4

-after implantation trophoblast differentiate into syncio- (invades endometrium) & cyto-trophoblasts
-syncio. invade endometrium & forms chorionic villi and increase s.a
-epiblasts diff. into extramembryonic membrane
-extra. invades core of chorionic villi
-villi get vasculared withing each extra.
-syncio. + cyto. + fetal capillaries+ surrounding extracellular mtrix = placenta barrier- facilitates exhange & protects
-maternal endometrium becomes decidua basalis. supoorts growing villi & helps form maternal part of placenta
-decidua basalis + villi = basal plate of placenta - maternal blood sinuses are stabilished here
-amnion + chorion = amniochorionic fluid which ecloses fetus with fluid
-throughout pregnancy placenta matures, s.a & vascularization increase. End of trhirs sem. fully devlopped

function: hormone production/ exchange of nutrients & gases / protection