Early Stages Flashcards
When is pregnancy calculated?
From the last menstrual period (LMP)
When is development calculated from?
Fertilisation
What is an oocyte?
The egg cell
Where is the egg released from?
Ovary
How is the oocyte swept into the oviduct?
The frimbriae
Meiosis is only completed when?
When the sperm enters
What is cleavage ?
Rapid mitotic cell division
Where does the pre-embryo implant?
Into the uterine wall?
What is a zygote?
A fertilised egg
What does the zygote divide to form?
Blastocyst
What can be seen in maternal blood when blastocyst is formed? (2-3 days)
EPF (early pregnancy factor)
What is a blastocel?
A hollow ball of cells formed from a zygote
What will the inner cell mass of the blastocel form?
The embryo
What will the outer cells of the blastocel form?
The trophoblast will form the placenta
What forms the chorion?
The trophoblast
What is the chorion?
Part of the placenta which enables the fetus to get O2 and nourishment from the mother
What is the zona pellucida?
A membrane which surrounds the blastocyst to protect it
Before implantation, what does the blastocyst need to do?
Hatch from the zona pellucida
What happens at day 6?
The blastocyst attaches to uterine wall
What is the risk of the blastocyst being able to implant anywhere?
Ectopic pregnancy
What happens if the blastocyst does not implant?
It will leave in menstruation
Day 14 may show spotting in the mother and may be mistaken for a period. What does this signify?
The blastocyst being fully embedded
What would happen if the blastocyst implants close to the cervix?
The placenta would not be able to be shed so a c-section would be planned
What happens to the uterine cavity as the blastocyst grows?
It is pushed together until gap is almost gone
What does the trophoblast form when it divides?
The cytotrophoblast and the syncytiotrophoblast
What is the characteristic of the cytotrophoblast?
It forms tightly packed cells around the blastocyst
What are the characteristics of the syncytiotrophoblast?
Loosely packed cells surrounding the cytotrophoblast
What are Lacunae and where do they form?
They are ‘holes’ formed between the loosely packed cells of the syncytiotrophoblast
How does the lacunae fill with blood?
The trophoblast cells invade spiral arteries causing a leakage of blood into the lacunae, giving the fetus a blood supply
What is the epiblast?
The cell mass in the blastocyst which will form the embryo
Some of the cells in the epiblast go on to form what?
The amniotic cavity
What does the cytotrophoblast form as it grows?
Villi- primary (frondosum)
There is always a membrane separating the embryo from the maternal tissue, what forms this?
The syncytiotrophoblasts that form the Chorion
How is the maternal blood supply invaded?
The primary villi grow to form secondary and tertiary villi, forming villi trees which invade the lacunae and also maternal blood supply
What is the amniochoronic membrane and what does it do?
Syncytiotrophoblast invades uterine tissue forming the chorion which fuses with the amnio layer. This allows the fetus to get O2 and nourishment
What a the placenta?
An organ which provides the fetus with nourishment via the umbilical cord.
