Fetal Development

Question 1

Explain the steps of fetal development.

Answer 1

1. Penetration of the corona radiata (1st stage)
2. Species recognition, acrosome reaction (2nd stage)
3. Penetration of the zona pellucida, cortical reaction.
4. Gamete fusion
5. Meiosis completion

Question 2

Explain the steps of gastrulation.

Answer 2

1. Cells from the epiblast migrate inwards creating a primitive streak.
2. The ectoderm creates a pipe in the mesoderm. (notochordal process).
3. When pressures are equal notochordal plate fuses and closes the connection between cavities.
4. Closed pipe of ectoderm=notochord.
5. At the end of gastrulation we have an embryonic disc with notochord in middle and mesoderm at the 2 ends of the disc.
6. Mesoderm thins to form 2 membranes: 1. oropharyngeal (mouth) and 2. cloalical (genitals and anus).

Question 3

Explain the steps of placental development.

Answer 3

1. The trophoblast grows and expands into the placenta.
2. Cells specialise into 2 layers- cytotrophoblast and synciotrophoblast.
3. Placenta starts to produce ACG to maintain pregnancy.
4. Synciotrophoblasts continues growing into placenta in chorionic villi.
5. Chorionic villi grow around pools of blood to feed pregnancy and pools of blood grow to connect with maternal blood.
6. Cells of synciotrophoblast degenerate and are replaced by cells of cytotrophoblast forming the chorionic membrane.

Question 4

What does the epiblast and hypoblast do?

What does the amnioblast do?

Answer 4

The epiblast fills with fluid to form amniotic fluid.
The hypoblast fills with fluid to form the yolk sac.
The amnioblast surrounds the baby and becomes amnion (internal placenta membrane)

Question 5

What happens when the bilaminar disc becomes trilaminar?

Answer 5

Part of the mesoderm develops blood vessels through the cytotrophoblast to connect the embryo with the chorionic villi and the maternal circulation-Primitive Ambilical Chord