Embryology Flashcards
State the phases of embryological changes
Pre-embryonic 0-3 weeks
Embryonic 4-8 weeks
Foetal phase 9-40 weeks
Postnatal
Fertilisation of zygote
ovum (oogenesis) + sperm (spermatogenesis) = ZYGOTE (diploid)
What happens to the zygote?
Keeps dividing (2,4,8..) to form a ball of cells called a MORULA
What happens to the morula?
Cells keep dividing and start to increase in number
A blastocystic cavity forms, cells form in the INNER CELL MASS and the outer lining is called TROPHOBLAST(forms umbilical cord)
What happens to the blastocyst?
Blastocyst travels to the uterine cavity and later on implants into it (at start of week 2)
What does the blastocyst need in order to reach the uterine cavity?
It needs healthy ciliated epithelium in Fallopian tube
What happens to the blastocyst when it reaches the uterine cavity?
It implants into the uterine endometrial layer
What happens to the trophoblast?
It is formed of many cells
It develops into CHORION
What does the chorion do?
It develops the placenta
It secretes human chorionic gonadotropin
It forms the implantation process
What does the human chorionic gonadotropin do?
It helps maintain the endometrium
What happens to the inner cell mass?
It forms a 2 layer flat with an amniotic cavity on top of the EPIBLAST and
A yolk sac below the HYPOBLAST
What does the placenta do?
Foetal nutrition
Transport of waste and gases
Immunity
What forms the placenta?
The chorion
Summary of week 1&2
zygote - morula - blastocyst with inner cell mass - amniotic cavity + yolk sac
morula - uterine cavity and blastocyst implants into it - chorion forms from trophoblast - placenta and decide basalis forms
What happens to the epiblast?
- Primitive streak forms in the midline
- Epiblast cells migrate between the epiblast and hypoblast
- They then displace the hypoblast
- They also form 3 germ layers: Ectoderm, Mesoderm and Endoderm
