Implantation - Anatomy & Physiology

• Implantation is critical to the survival of the embryo; the embryo must adhere and embed itself in the endometrium in order to exchange waste and nutrients. For this reason, the first differentiation of cells is into trophoblasts and syncytiotrophoblasts and the inner cell mass (ICM).
  • Trophoblastic cells posses adhesion molecules to adhere to the endometrium whilst ICM cells form the organism.

The extent of cellular growth and division and the time taken for implantation differs between species.

• Shortly after implantation cells of the ICM differentiate into different layers:

1. Epiblast - facing towards the uterine lumen, adjacent to syncytiotrophoblasts.
2. Hypoblast - facing towards the endometrium, adjacent to the blastocyst cavity.
3. Amnioblasts - cells of the epiblast that migrate up and around to allow the amniotic cavity to form.

• After gastrulation the epiblast gives rise to the three germ layers:

1. Ectoderm
2. Mesoderm
3. Endoderm

• The hypoblast gives rise to no persisting structure in the adult.