By Cristina Mestre Ferrer BSc, MSc (embryologist).
Last Update: 07/16/2014

It is likely that it is during the fourth week of pregnancy when you find out you are pregnant, maybe because you have noticed a delay in your menstruation. If so, and in case you are feeling something is going on inside you, you should better visit your gynecologist to confirm your suspicions and therefore evaluate if you are really expecting a baby.

The future baby, now called embryo, is a tiny organism the size of a bean. Despite it is still on its early stages, gastrulation has already occurred. It is a pivotal early development process that takes place during the first month of gestation.

The different sections of this article have been assembled into the following table of contents.

What is gastrulation?

Gastrulation is the process in which three layers of tissue are formed. All the tissues of the baby will be formed from these layers, which are the endoderm, the mesoderm and the ectoderm.

  • Ectoderm: this layer will originate the nervous system, the skin, the mouth, and the externals parts of the body.
  • Mesoderm: the muscular, skeletal, and all the veins and arteries that form the circulatory system will be rendered from this layer.
  • Ectoderm: in the deepest layer most of the organs of the baby will be formed, that includes the lungs and the digestive system.

The main processes taking place in the embryonic development are blastulation, gastrulation and organogenesis (organ formation). Once the embryo reaches the aforementioned stage, all the organs will begin their development in each corresponding layer until being completely formed and the baby is ready to be delivered.

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Authors and contributors

 Cristina Mestre Ferrer
BSc, MSc
Embryologist
Bachelor's Degree in Biological Sciences, Genetics & Human Reproduction from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Embryologist at IVI Barcelona. More information
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