University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

278

Pages:

3
Author:

Mariam A. A.

Week 2 Development of nutrient support systems Embryonic development • • At the end of week 1/start of week 2, we become bilaminar Epiblast and hypoblast = embryonic disc Placental development • • Syncytiotrophoblast continues to invade, eventually contacting uterine capillaries Syncytiotrophoblast produced βhCG (maintain ovarian hormone function) Extraembryonic development • • • • • Structures that form in week 2 – amnion and cavity, umbilical connecting stalk/allantois, chorion and sac Amnion – initially “dorsal” extension of epiblast with fluid cavity abutting the epiblast layer Amnion grows and folds with embryo Amniotic cavity expands to fill chorionic cavity (amnion and chorion will eventually meet) Connecting stalk – extension by which embryo remains attached to placenta, umbilical vessels will form within Extraembryonic development • Chorion – forms from hypoblast-derived extraembryonic mesoderm • • • • Cavity forming in extraembryonic mesoderm -> chorionic cavity (= extraembryonic coelom) Around embryo, chorionic cavity disappears as amniotic cavity grows In placenta, chorion develops into villi, which are bathed in maternal blood Hypoblast cells -> extraembryonic endoderm -> yolk sac Eventual placental circulation • CVS for prenatal testing samples chorionic villi Extraembryonic development • • • • Yolk sac – role in nutrient transfer in early implanted embryo via blood vessels that form in mesoderm walls Blood cell development until liver takes over in week 6 Blood vessels develop into umbilical blood vessels Secondary (definitive) yolk sac can be seen by ultrasound Extraembryonic development • • • Prechordal plate – thickening of hypoblast cells at one site of embryonic disc Site of future mouth Important in location of future head region End of Week 2 Key concept Embryo completes differentiation to bilaminar disc • Trophoblast expands dramatically to complete implantation • Syncytiotrophoblast degrades endometrial tissue to seek nutrient supply • Amnion/amniotic cavity; chorion/chorionic cavity; connecting stalk and yolk sac all form to support nutrient exchange and protect the developing embryo • Thickened hypoblast region forms prechordal plate (future