Extraembryonic Membranes Flashcards
(20 cards)
What are extraembryonic membranes (EEMs)?
Structures that support the embryo but don’t contribute to the embryo proper
What are the four main EEMs in mammals?
Chorion, amnion, yolk sac, allantois
What is the chorion derived from?
Trophectoderm + extraembryonic mesoderm
What is the function of the chorion?
Forms the foetal part of the placenta and mediates gas exchange
What is the amnion derived from?
Amnioblasts from the epiblast
What does the amnion do?
Secretes amniotic fluid to protect and cushion the embryo
When does the amnion form?
During early development as epiblast cells separate
What is the yolk sac derived from?
Hypoblast (primitive endoderm)
What are key functions of the yolk sac?
Nutrient transfer, blood cell production, and PGC origin
What does the yolk sac form first?
Blood islands for early haematopoiesis
What is the allantois derived from?
Posterior primitive streak/ hind gut endoderm
What is the function of the allantois?
Waste removal and blood vessel formation for the placenta
What does the allantois contribute to in adults?
The urachus (median umbilical ligament)
What structure houses all EEMs and the embryo?
The chorionic cavity
What connects the embryo to the placenta?
The umbilical cord
What are chorionic villi?
Projections that increase surface area for exchange in the placenta
What is Wharton’s jelly?
Gel-like connective tissue in the umbilical cord
Which EEM contributes to placenta formation?
Chorion (trophoblast)
What is the function of the placenta?
Exchange of gases, nutrients, and wastes; hormone production
What hormones are secreted by the placenta?
hCG, progesterone, hPL
