Pre-Implantation

Question 1

What are the stages of implantation?

Answer 1

• embryo hatching
• apposition
• adhesion
• invasion

Question 2

Describe embryo hatching

Answer 2

• day 6/7 after fertilisation, zona pellucida degenerates and blastocyst is released
• lytic factors from endometrial cavity involved
• blastocyst probably produces factors too

Question 3

Describe apposition

Answer 3

• earliest contact between blastocyst wall, trophoectoderm and endometrial epithelium
• occurs in crypt of endometrium

Question 4

Describe adhesion

Answer 4

• limited time window
• complex interactions between trophoblast and maternal epithelium
• trophoblast attaches to uterine epithelium by microvilli of trophoblast
• integrin receptor family involved

Question 5

Describe invasion

Answer 5

• syncytiotrophoblast cells flow into endometrium causing oedema, glycogen synthesis and increased vascularisation (decidualisation)
• pregnant endometrium is now decidua
• nutrition still dependent on uterine secretion and tissues
• breakthrough bleeding can occur