Lecture 31 - Embryology Week 2

Question 1

when does blastocyst hatching and initiating implantation happen

Answer 1

days 5-6

Question 2

What does a blastocyst consist of

Answer 2

embryoblast and trophoblast

Question 3

What occurs during implantation at 7 days

Answer 3

trophoblast and embryoblast differentiate
trophoblast - syncytiotrophoblast and cytotrophoblast

embryoblast -epiblast and hypoblast

Question 4

What is the significance of becoming bilaminar

Answer 4

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

Question 5

epiblast forms which surface

Answer 5

dorsal surface

Question 6

hypoblast forms which surfac

Answer 6

ventral

Question 7

Where does the amniotic cavity form

Answer 7

small fluid filled cavity in epiblast

Question 8

How does the embryoblast receive nutrients

Answer 8

Syncytiotrophoblast erodes walls of maternal capillaries to establish uteroplacental circulation

Question 9

What also happens when syncytiotrophoblast erodes walls of maternal capillaries?

Answer 9

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

Question 10

What is the chorionic cavity and when does it form

Answer 10

a cavity that forms in the extra -embryonic mesoderm.

12-13 days

Question 11

Secondary yolk sac

Answer 11

a second wave of hypoblast cells migrate to form a secondary (definitive) yolk sac – pushing the primary yolk sac away from the embryo

Question 12

What happens when the secondary yolk sac develops

Answer 12

primary yolk sac degenerates

Question 13

What are the embryo within the amniotic cavity and secondary yolk suspended by

Answer 13

connecting stalk

Question 14

How are the syncytiotrophblast relevant to pregnancy testing

Answer 14

secrete HCG hormone

Helps maintain endometrium and may play a role in maternal immunotolerance.

Question 15

abnormal implantation site

Answer 15

intestinal loop

Question 16

placenta previa

Answer 16

can cause severe bleeding in late pregnancy

Question 17

tubal implantation

Answer 17

majority of ectopic pregnancies occur in uterine tube

Question 18

How does abdominal implantation occur

Answer 18

there is a gap between the ovary and uterine tube therefore fertilised egg can enter the abdomen

Question 19

Lithopaedion

Answer 19

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

Question 20

hydatidiform mole

Answer 20

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