Lecture 31 - Embryology Week 2 Flashcards
(20 cards)
when does blastocyst hatching and initiating implantation happen
days 5-6
What does a blastocyst consist of
embryoblast and trophoblast
What occurs during implantation at 7 days
trophoblast and embryoblast differentiate
trophoblast - syncytiotrophoblast and cytotrophoblast
embryoblast -epiblast and hypoblast
What is the significance of becoming bilaminar
this is the first stage of organisation of the body plan
establishes dorsal and ventral axis of embryo
-epiblast forms the dorsal surface and hypoblast ventral surface
epiblast forms which surface
dorsal surface
hypoblast forms which surfac
ventral
Where does the amniotic cavity form
small fluid filled cavity in epiblast
How does the embryoblast receive nutrients
Syncytiotrophoblast erodes walls of maternal capillaries to establish uteroplacental circulation
What also happens when syncytiotrophoblast erodes walls of maternal capillaries?
a new layer of tissue between primary yolk sac and cytotrophoblast - extraembryonic mesoderm is formed
- this connective tissue is derived from the yolk sac and eventually covers the amniotic sac too
What is the chorionic cavity and when does it form
a cavity that forms in the extra -embryonic mesoderm.
12-13 days
Secondary yolk sac
a second wave of hypoblast cells migrate to form a secondary (definitive) yolk sac – pushing the primary yolk sac away from the embryo
What happens when the secondary yolk sac develops
primary yolk sac degenerates
What are the embryo within the amniotic cavity and secondary yolk suspended by
connecting stalk
How are the syncytiotrophblast relevant to pregnancy testing
secrete HCG hormone
Helps maintain endometrium and may play a role in maternal immunotolerance.
abnormal implantation site
intestinal loop
placenta previa
can cause severe bleeding in late pregnancy
tubal implantation
majority of ectopic pregnancies occur in uterine tube
How does abdominal implantation occur
there is a gap between the ovary and uterine tube therefore fertilised egg can enter the abdomen
Lithopaedion
can occur when an abdominal pregnancy remains undiagnosed and foetus dies
foetus too large to be reabsorbed - instead calcifies
this is thought to protest the mother from necrotic tissue of foetus
hydatidiform mole
Development of the trophoblast without any embryonic tissue
Due to fertilisation of an ‘empty’ egg lacking a nucleus
Suggests that paternal genes favour the formation the trophoblast at the expense of the embryo – parental imprinting
Syncytiotrophoblast produces hCG giving a positive pregnancy test
