Flashcards in Lect. 17 - Extraembryonic Tissues And Placenta Deck (21):
What germ layers are the extra embryonic layers derived from?
Amnion: ICM - epiblast derivative - ecto and meso
Yolk Sac: ICM - hypoblast derivative - endo and meso
Chorion: fetal maternal interface - ecto and meso
Allantois: ICM, interfaces w/ placenta - endo and meso
What are the two trophoblastic derivative that comprise the fetal-maternal interface?
Placenta and chorion
What are the functions of the amnion?
Buffer against mechanical injury; accommodates growth; allows normal movements; protects fetus from adhesions
Excessive amount of amniotic fluid (>2000 mL). Related to esophageal atresia and anencephaly
Too little amniotic fluid (
What info can be learned by testing for a-fetoprotein?
High concentration of a-fetoprotein is a strong indicator of NT defect
What info can be learned by testing for creatine and lecithin-to-sphingomyelin ratio?
Fetal maturity can be assessed by determine the concentration of creatine or the lecithin-to-sphingomyelin ratio (reflection of the maturity of the lungs)
What are the 4 extra embryonic layers?
Amnion, yolk sac, chorion, alantois
Phase I of the formation of the amniotic fluid
1st 20 weeks of pregnancy; free diffusion of electrolytes through fetal ectoderm; maternal serum; secretion by amniotic membrane
Phase II of formation of amniotic fluid
Contributions from fetal urine; filtration for vessels associated w/ chorion laeve (smooth chorion)
Known and possible functions of the yolk sac in mammals?
May concentrate folic acid and vitamins A, B12, and E; other functions: site of origin of primordial germ cells; location of blood islands (origin of initial blood cells (extraembryonic hematopoiesis)
Some evidence shows that before the placental circulation is established, nutrients (folic acids and vitamins) are concentrated in the yolk sac and are absorbed - happens during neurulation so may help prevent NTDs
Traces of the yolk duct persists as a fibrous cord or outpouching of the small intestine
Where do their allantoic (umbilical) vessels develop?
In the mesoderm of the allantois
Proximal part of the allantois = urachus; associated w/ the formation of the urinary bladder; becomes the median umbilical ligament
What tissue in the mature placenta directly interfaces w/ the maternal uterine CT?
Extraembryonic mesoderm overlaid w/ trophoblast
Villi and outer surface of chorionic plate are bathed in a sea of continually exchanging maternal blood
Formed by expansion of the cytotrophoblastic columns over the maternal decidual cells