Embryo

A embryo (of the old Greek ἔμϐρυον / émbruon ) is a organization in development since the first division of the egg or Zygote until the stage where the principal bodies are formed.

The Embryologie is the study of the growth of an organization during all gestation, i.e. at the same time for the embryonic period and the fetal period.

The Tératologie is the study of the abnormal embryo .

At the human one

In the human being , the embryonic stage lasts eight weeks is ten weeks of Aménorrhée. This period corresponds to the formation of the bodies. Beyond and until the term of the Pregnancy, one speaks about Fœtus corresponds to the maturation of the bodies.

Development

The development of the embryo of the majority of the Métazoaire S includes/understands successively:

  • the cleavage or the segmentation which corresponds to the first Mitose S of the embryo.

  • the Gastrulation which sets up both (Ectoderme, Endoderme) or three (+ Mésoderme) layers embryonic which will form fabrics and bodies characteristic of the species. The organization of the embryo is often upset during this process which implies many cellular migrations.

  • the Neurulation and the Organogenesis during which the nervous system and the bodies are formed starting from the layers.

The embryos of the métazoaires can breathe is by direct diffusion through the Tégument (example: embryos of Amphibian S), is using an embryonic appendix which plays the part of " Lung " or of " Gill " transient (embryos of Amniote S, for the majority of the Mammifère S it is the Placenta which ensures this role).

The embryos of the métazoaires can be nourished starting from the reserves contained in their cells and deposited initially in the Ovocyte by their mother (embryos of Arthropode S, Amphibians), or are nourished using embryonic appendices (embryos of amniotes, for the majority of the mammals it is the Placenta which ensures this role).

At the plants

In Botanical, the embryo is the whole of cell S exits of the division of the egg until the stage of the Plantule, organization maintained in latent Vie, for a variable time, within the Graine and which includes/understands four parts: the Gemmule, the Tigelle, it (S) cotyledon (S) and the Radicle.

Polyembryony

See too

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