By Cristina Mestre Ferrer BSc, MSc (embryologist).
Last Update: 08/19/2015

Gastrulation is a vital process that takes place during the development of the embryo. During the pregnancy there are some changes that make it possible for a zygote -a one-cell embryo- to become a healthy and fully developed baby.

At day five, the embryo is a single-layered blastula with two types of cells; a single layer of cells named trophoblast and the inner cell mass. This inner mass will eventually give rise to the final structures of the fetus. The first stage of this changing process is the gastrulation. Therefore, gastrulation is, probably, the most important stage in the development of the embryo, because all its tissues start grow at this stage.

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


The gastrulation is defined as the process in which three germ layers are formed: the ectoderm, mesoderm and endoderm.

From the blastula -early developmental stage of the embryo- there is a series of cell migrations and cell fusions that will make up three well diferenciated layers. From these layers all the tissues of the baby-to-be are made.

The gastrulation takes place during the third week of the embryo’s life and, since it is an early developmental stage, it is included in the first trimester of the pregnancy.

Germ layers

Thanks to the process of gastrulation, the germ layers are formed, and each of them are intended for creating a different type of tissue; henceforth, all the tissues of the embryo will be created.


It is the outer layer and the first to be created. It encloses the embryo. This layer is the responsible for the creation of the skin, the epithelium of the mouth, cornea, the mammary glands glande and the nervous system.


It is the middle layer, but it’s created in the last place. It is the responsible for the tissues in the circulatory system, the excretory system, muscles, the bones and also the reproductive system.


It is the inner layer of the embryo and the second to be created. It is from the endoderm that the majority of the inner organs are created, such as the digestive system, the glands and the respiratory system.

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Authors and contributors

 Cristina Mestre Ferrer
BSc, MSc
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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One comment

    1. blossom91

      I find the process of gastrulation quite bizarre… In fact, I’ve never ever heard that word before and I had my son 2 years ago LOL! Very interesting post by the way… Thanks!