Embryo development

This is the process in which an organism develops from a single-celled zygote to a multicellular organism.

Embryo development is complex and well-regulated. Embryo development in humans is divided into following stages:

  • Fertilization

  • Cleavage stage

  • Blastula stage

  • Gastrulation

  • Organogenesis

  • Vertebrate formation

Nine weeks after fertilization, the human embryo is considered a fetus. There is no clear feature that distinguishes an embryo from a fetus. The term fetus implies that the embryo can be recognized as a human.

The embryo is pinkish against a red background. The embryo has a slightly rounded portion at one end, with an elongated tail like section curving in to form a C shape. Two small protrusions can be seen on the side, where limbs will later form.

7 weeks old human embryo from Anatomy & Physiology, Connexions Web site.

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