Fertilisation & Implantation

Question 1

What is fertilisation?

Answer 1

Fusion of male and female gametes

Question 2

Where should fertilisation occur?

Answer 2

Ampulla (middle) of uterine tube

Question 3

Describe fertilisation.

Answer 3

1. Sperm and ovum fuse
2. The 2 pronuclei fuse and all 46 chromosomes line up
3. CLEAVAGE
   fertilised egg divides in to 2 halves, this continues. By day 3 there are 8 cells
4. COMPACTION
   cells flatten

5. CAVITATION & DIFFERENTIATION
epithelial layer (trophectoderm) formation

6. EXPANSION
7. HATCHING
   Zona pellucida ruptures

Question 4

What does the sperm have to do to fertilise the egg?

Answer 4

Penetrate the entire Zona pellucida of the ovum

Question 5

What is the Zona pellucida?

Answer 5

Thick transparent membrane surrounding the ovum before implantation

Question 6

Name the stages of fertilisation (there are 6!)

Answer 6

1. Fertilisation
2. Cleavage
3. Compaction
4. Cavitation & differentiation
5. Hatching

Question 7

Describe implantation.

Answer 7

1. Trophoblast and endometrium synchronise - apposition
2. Surface endometrial cells express adhesion molecules. Trophoblast cells express integrins. They attach
3. Trophoblast invades endometrium
4. Progesterone causes endometrial stromal cells to differentiate into secretory cells.
   They secrete growth factors and nutrients to support growth of blastocyst
5. IL-2 is secreted by leukocytes in endometrium - prevents maternal recognition of embryo as foreign

Question 8

What is IL-2?

Answer 8

It is secreted by leukocytes in endometrium

Prevents maternal recognition of embryo as foreign