Week 2 of Embryo Development: Full Implantation and Bilaminar Disc Formation

At what time stamp do embryos organise themselves into embryoblasts and trophoblasts?

at the morula time stamp

How many cells are in a morula?

16-32

What two groups of cells do embryos first organise themselves into?

embryoblasts and trophoblasts

What day does the blastocyst implant?

5-6

What two groups of cells do trophoblasts differentiate into?

cytotrophoblasts and syncytiotrophoblasts

What two groups of cells do embryoblasts differentiate into?

hypoblasts and epiblasts

What is the bilaminar disc?

the flat, round, pancake-like layer of epiblasts and hypoblasts

What is the name of the initial cavity in embryos?

blastocyst cavity

True or false: syncytiotrophoblasts are multinucleate?

true

What prevents the mother's immune system from attacking the embryo?

syncytiotrophoblasts

How are syncytiotrophoblastic cells formed?

cytotrophoblasts dump and lose their membrane

On what day does the amniotic cavity form?

day 8

Where is the amniotic cavity formed?

In the epiblast layer

What two cell groups invade the uterine wall?

cytotrophoblasts and syncytiotrophoblasts

What is the first stage of organisation of the body plan?

becoming bilaminar

Fill in the gap: the epiblasts form the ______ surface of the embryo

dorsal

Fill in the gap: the hypoblasts form the ______ surface of the embryo

ventral

On what day is Heuser's membrane formed?

day 9

What is the name of the membrane formed by hypoblasts migrating around the embryo?

Heuser's membrane

How does the embryo get resources by day 9?

syncytiotrophoblasts penetrate a uterine gland and a maternal capillary

What is established once syncytiotrophoblasts penetrate a maternal capillary?

a utero-placental blood supply

How does blood reach the embryo from the capillary?

it enters through fluid filled cavities in the syncytiotrophoblast layer

What is the name of the layer between cytotrophoblasts and the Heuser's membrane?

extraembryonic mesoderm

Where does the chorionic cavity form from?

extraembryonic mesoderm

On what day does the chorionic cavity form?

day 12-13

What forms the extraembryonic mesoderm on day 12-13?

chorionic cavity

What day does the definitive yolk sac form?

12-13

Where is the chorionic cavity located?

ventral to the hypoblast layer inside the extraembryonic mesoderm

What is another term used to describe the fluid filled cavities in the syncytiotrophoblast?

trophoblastic lecuna

What is the name of the branch of extraembryonic mesoderm that holds the hypoblast and epiblasts?

connecting stalk

True or false: all remnants of the primary yolk sac are removed by the end of week 2

false

What is the name of the large cavity that takes up most space by the end of week 2?

chorionic cavity

What do syncytiotrophoblasts secrete?

hCG

What hormone is used in pregnancy testing?

hCG

What does hCG do?

maintain the endometrium

What is the name given to abnormal implantation sites?

ectopic implantations

Where should the embryo implant?

the uterine lining

Where does fertilisation take place?

ampulla

Describe placenta previa:

placenta develops in the birthing canal which can cause the placenta to rupture under the weight of the foetus

What is the name of the condition where the placenta develops in the birthing canal?

placenta previa

What is used to reduce the impact of placenta previa?

use a C section

What % of ectopic pregnancies occur in the ampulla?

80%

What is the common result of tubal implantations?

tube ruptures

Why is it that abdominal implantations can take place?

there is a gap between the ovary and uterine tube

What is the common result of abdominal implantations?

miscarriage

What is the name given to the calcified foetus formed by abdominal implantations?

lithopaedion

What causes a lithopaedion to form?

an abdominal pregnancy remains undiagnosed causing the foetus to die

What is a lithopaedion?

a calcified foetus formed to protect the mother from necrotic tissue

How are hydatidiform moles formed?

a sperm fertilises with an egg lacking a nucleus resulting in the development of the trophoblast without any embryonic tissue

What is the name of the embryonic complication characterised by the development of the trophoblast without any embryonic tissue?

hydatidiform moles