Implantation, Placentation And Hormonal Changes Flashcards
What is a blastocyst?
→ An embryo at the 5th or 6th day of development
What does the embryoblast give rise to?
→ The fetus
What are the three layers of the blastocyst?
→ Trophoblast
→ Blastocoel
→ Embryoblast
What does the trophoblast give rise to?
→ The placenta
What is the blastocoel?
→ The fluid filled cavity
What are the two things needed for implantation to occur?
→ The blastocyst has to be fully mature
→ A receptive endometrium is needed which expresses receptivity markers to communicate with the blastocyst
Describe hatching
→The blastocyst hatches out of the zona pellucida due to expansions and contractions
→ this herniates the blastocyst out of the zona
→ digestive enzymes break down the opposite pole of where the blastocyst is
Where do the enzymes dissolve the zona?
→ Abembryonic pole
What are the three stages of implantation?
1) Apposition
2) Attachment
3) Invasion
What is Apposition?
→ Close positioning of the blastocyst to the endometrium
What is Attachment?
→ Cells of the trophoblast attaching to endometrium
What is Invasion?
→ Trophoblast cells multiply and invade the endometrium
Describe how the embryo implants (days 7-11)
→ The blastocyst attaches itself to the surface of the endometrial wall (decidua basalis)
→ Trophoblast cells start to assemble to form a syncytiotrophoblast to facilitate invasion
→ Syncytiotrophoblast further invades the decidua basalis and by day 11 it is almost completely buried
Describe the decidual reaction
→ High levels of progesterone results in the enlargement and coating of the decidual cells in glycogen and lipid-rich fluid
→ the fluid is taken up by the syncytiotrophoblast and helps sustain the blastocyst early on before the placenta is formed
What is a syncytiotrophoblast?
→ A group of trophoblast cells which are multinucleated
How are primary villi formed?
→ Cells of the syncytiotrophoblast start to protrude out to form tree-like structures known as primary villi which are formed around the blastocyst
→Day 14
How are lacunae formed?
→ Decidual cells between the primary villi begin to clear out leaving behind empty spaces known as lacunae
→ around day 14
How does the junctional zone form?
→ Maternal arteries and veins grow into the decidua basalis
→ Blood vessels merge with the lacunae
→ Arteries fill the lacunae with oxygenated blood
→ Veins return the deoxygenated blood to the maternal circulation
→ Blood filled lacunae merge to a single large pool of blood connected to multiple arteries and veins
→this is known as the junctional zone
When is the umbilical cord formed?
→ Around week 5
Describe how chorionic frondosum form?
→ Day 17 the fetal mesoderm cells start to form blood vessels within the villi
→ a basic network of arteries, veins and capillaries
→ capillaries connect with blood vessels in the umbilical cord
→ villi grow larger in size and develop into chorionic frondosum
What separates maternal and fetal blood cells?
→ The outer lining of the primary villi is in contact with the junctional zone
→ The lining of the endothelial cells of the decidual from the mothers side
When do the decidual septa form?
→ 4th and 5th month
What is the function of decidual septa?
→ They divide the placenta into 15-20 regions
→ This gives it a much larger surface area in contact with the maternal blood
What is the umbilical cord made up of?
→ Two arteries and one vein