Fertilization & development

10 important questions on Fertilization & development

When does cleavage start?

Cleavage starts immediately after fertilization.

What is the route of zygote during cleavage?

A zygote becomes a pre-embryo, which develops into a multicellular blastocyst. Cleavage ends when the blastocyst contacts the uterine wall.

At a certain point the cells are very compact (can't distinguish the separate cells). What causes this?

This is because of E-cadherin.
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How can the 'compaction' of an embryo be prevented?

Anti-E-cadhering prevents the 'compaction' or an embryo.

Where does the embryo arise from?

A blastocyst is formed, a group of cells in this hollow ball forms the inner cell mass (ICM). The ICM develops into the embryo. The outer cells, called trophoblasts, become the extra-embryonic membrane.

What are the functions of the extra-embryonic membrane?

  • Role in implantation
  • Supports embryo's growth

What is the result of hatching?

The result of hatching is that the blastocyst is out of the zona pellucida and the uterine fluid can now feed the pre-embryo.

What do trophoblasts synthesize?

Trophoblasts synthesize human chorionic gonadotropin hormone (hCG). hCG signals to the corpus luteum to increase size and progesteron production.

How does the inner cell mass form into a human being?

Two processes:
  • Gastrulation
  • Organogenesis

What is the status of the embryo in the second week?

  • Two cell types present
  • Two layers are formed
  • Two cavities are formed: from which two of the extra-embryonic membranes are formed (4 in total)

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