So let's summarize everything we've talked about in this module.
In a nutshell, the germinal stage begins with conception and ends after two weeks.
The embryonic stage picks up at the two-week mark and it ends at the end of eight weeks.
The fetal stage begins at nine weeks and it continues until the baby is actually born.
The trophoblast makes up the outer layer of the blastocyst and it becomes the chorionic villi.
The ectoderm will become parts of the baby that are related to sensory activity,
while the mesoderm will become the structural things like bones
and muscles and connective tissue.
The endoderm will become the epithelial lining and it lines the GI tract, things like that.
The type of twin formation is formed by when the cells divide
and whether there's one zygote or two.
The chorion and the amnion are separate layers that are sealed together on the amniotic sac.
The decidua basalis will become the placenta.
Maternal and fetal blood never, never mix.
There are two arteries and one vein.
The placenta fulfills the function of the liver and the lungs.
Remember, placentas are awesome.
Oxygenated blood via the umbilical veins
will mostly bypass the liver through the ductus venosus.
Oxygenated blood also bypasses the lungs via the foramen ovale.
Deoxygenated blood bypasses the lungs via the ductus arteriosus
and it returns through the umbilical arteries.
We're done, you did it.
Remember, go back and review and you'll have it down perfectly.