Explain the complete process of implantation, from the arrival of the blastocyst in the uterine cavity to the formation of the placenta, highlighting the roles of the trophoblast, decidua, cytokines, and maternal blood vessels.
Answer
The blastocyst attaches to the decidua, trophoblast invades the endometrium forming villi, cytokines recruit maternal immune cells, decidual stromal cells remodel, and maternal spiral arteries are remodelled to supply blood, forming the placenta.
Step-by-step solution
- State that after fertilisation, the zygote divides into a blastocyst by day 5 and reaches the uterine cavity.
- Explain that the trophoblast differentiates into cytotrophoblast and syncytiotrophoblast, which attach to the decidualised endometrium.
- Describe how the syncytiotrophoblast secretes enzymes and cytokines that penetrate the stromal matrix, initiating invasion.
- Mention the recruitment of maternal immune cells (macrophages, NK cells) mediated by cytokines to modulate invasion.
- Explain how decidual stromal cells remodel the spiral arteries to increase blood flow and reduce resistance.
- State that as invasion continues, the trophoblast forms chorionic villi that connect with maternal blood, establishing the placenta.
- Summarise that by the end of the first trimester, a functional placenta is formed, enabling nutrient and gas exchange.
Common mistake: Forgetting the role of cytokines and maternal blood vessel remodeling.
Concept tested: Implantation and placental formation
Published · How this solution was prepared and checked
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