extraembryonic sacs

Question 1

amnion function

Answer 1

protective sac for fetus to develop

Question 2

yolk sac function

Answer 2

• nutrient uptake from extraembryonic coelom
• protein synthesis e.g. alpha-fetoprotein
• first site of haematopoiesis

Question 3

outer surface of yolk sac has which transporter

Answer 3

GLUT1

Question 4

increased level of alpha fetoprotein in maternal circulation means

Answer 4

• abnormal placental permeability
• pathology
• fetal death

Question 5

are the amnion and yolk sac maintained throughout pregnancy

Answer 5

• amnion yes
• yolk sac regresses by 20w when placenta is established

Question 6

epiblast forms

Answer 6

• embryo
• amnion

Question 7

hypoblast (primitive endoderm) forms

Answer 7

primary yolk sac

Question 8

trophoectoderm forms

Answer 8

trophoblast of chorionic villi

Question 9

sequence of formation of extraembryonic sacs

Answer 9

1. primary yolk sac
2. secondary yolk sac
3. formation of extraembryonic coelom
4. obliteration
5. regression of yolk sac

Question 10

describe the formation of the primary yolk sac

Answer 10

• ICM divided into epiblast and hypoblast
• epiblast faces amniotic cavity, hypoblast faces blastocoel
• hypoblast extends over trophoblast and starts to differentiate into extraembryonic mesoderm that separates it from the trophoblast
• cavity surrounded by hypoblast: primary yolk sac

Question 11

formation of secondary yolk sac

Answer 11

primary yolk sac constricts and pinches off, leaving the secondary (definitive) yolk sac

Question 12

what happens while the secondary yolk sac is forming

Answer 12

• lacunae form in the extraembryonic mesoderm and coalesce to give rise to the extraembryonic coelom that will eventually surround the conceptus
• conceptus remains connected to the chorion by the connecting stalk (chorion = extraembryonic mesoderm + underlying trophoblast surrounding the extraembryonic coelom)

Question 13

describe the obliteration of the extraembryonic coelom and the regression of the yolk sac

Answer 13

• amnion expands around central embryo
• by 12w of pregnancy, amnion pushes against inner surface of chorion, obliterating the extraembryonic coelom
• yolk sac is connected to embryo by yolk sac stalk
• by 20w, has gradually regressed into umbilical cord