Embryology 1.3 Flashcards
What is implantation? (week 2 )
blastocyst burrows itself into the endometrial layer and stays there for 39 weeks after
Why is the blastocyst able to burrow into endometrial layer?
because of outer cell mass- trophoblast
What’s going to happen to the trophoblast ( the outer cell mass) ?
outer cell mass (initially a single layer) is going to divide and form two layers.
Cellular changes within cells until it becomes a chorion.
What is the chorion going to develop?
finger like processes called chorionic villi.
What are the functions of chorionic villi?
- Implantation process
- Forms part of the placenta in due course
- Secretes human Chorionic gonadotropin (HCG) (used to detect pregnancy)
Describe why the endometrium sheds?
Oestrogen and progesterone has a function of acting on this endometrium of the uterus and making it develop.
The endometrium keeps developing as long as the ovary keeps secreting this hormone. Hormones secreted for about 3 weeks and then ceased to be secreted.
What hormone does the chorion secrete to keep implanted embryo in endometrium?
Human Chorionic Gonadotropin
What does HCG encourage?
ovaries to keep producing oestrogen and progesterone
What has happened to the chorion at around weeks 12-15?
chorion developed into the placenta (has own system of blood vessels) and is now able to nourish the growing embryo
What are the side effects of HCG?
morning sickness
When does morning sickness disappear?
end of the first trimester
How do we detect pregnancy?
HCG in the urine
What is the decidua?
the endometrium after implantation has occurred
Recap of terminology?
zygote- first cell in the body that’s formed
morula- when zygote is divided and it forms that solid mass of cells
blastocyst- structure with cavity, outer and inner cell layer
trophoblast
chorion
What happens to the inner cell mass during second week?
inner cell mass going to flatten itself and form two layers.
The two layered flat disc is called the bilaminar disc
What are the two layers of the bilaminar disc called?
epiblast - top
hypoblast - hypoblast
What is the cavity above the epiblast called?
amniotic cavity
What is the cavity below hypoblast called?
yolk sac
What will form the embryo?
the bilaminar disc
What is completely covering the embryo?
amniotic sac
What happens to the yolk sac?
becomes smaller
What cavity also forms ?
allantoic cavity
What cavity are all these structures developing in?
the chorionic cavity
What will chorionic villi develop into?
the placenta
What are the main functions of the placenta?
foetal nutrition
transport of waste and gases
immune etc.
Describe foetal part and surface of placenta?
smooth with foetal blood vessels and end of umbilical cord
Describe maternal pat of the placenta?
decidua basalis of endometrium
rough and has maternal blood vessels
What carries blood into the placenta?
two umbilical arteries and one umbilical vein that carry blood up into the placenta
When does placenta start to form and when does it mature?
starts to form about week 12 but it matures by about 18 to 20 weeks
How much does placenta weigh?
At birth, 1/6 of foetus
How are non identical twins formed (fraternal/dizygotic)?
2 ova being released and two sperms
two zygotes
different genetic makeup
2 placentae
How are identical twins formed ?
zygote divides into two and each cell develops into a diff embryo
