Icon module 6

Learning aims

  • Describe the histological structures of the endometrium
  • Explain the phases of endometrial changes during the menstruation cycle
  • Know the effects of the hypophysial hormones in the regulation of the menstruation cycle
  • Explain the various stages of implantation
  • Know the fundamental mechanisms of the implantation at the molecular level
  • List the normal types of implantation and the anomalies of the extra-uterine pregnancies
  • List the various possibilities for hindering an implantation and thus a pregnancy

What you should already know

  • Fertilization
  • Preimplantation

Delving deeper

  • How is a coordinated maturation of the gamete and of the endometrium guaranteed so that optimal conditions for the development and implantation of the embryo are assured?
  • How, during the implantation period, are the nutritional requirements of the blastocyst assured before the utero-placental circulation begins?
  • Which mechanisms play a role in controlling the reactions of the endometrium to the presence of a blastocyst? This question arises because the blastocyst possesses a different genotype, and is invasive because of its high proteolytic activity.
  • Based on your knowledge of the implantation mechanisms of blastocysts, which measures could be employed to interrupt the further development of an embryo after an oocyte has been fertilized?


The implantation (nidation) of the blastocyst in the uterine endometrium, corresponding to Carnegie Stage 5, begins between the 6th and 7th day following the fertilization and ends around the 12th day with the formation of the primitive utero-placental circulation. A basic developmental stage is involved here that is absolutely necessary for the survival of the nutrient-poor blastocyst (the oocyte has no yolk). The implantation of the human embryo is interstitial, whereby the blastocyst is taken up in the endometrium and completely embedded there. This extremely important stage not only allows separation of the embryo from the outer world, it also makes an intimate contact with the maternal organism possible, guaranteeing the delivery of nutrients that are indispensable for further development.