Embryos

An embryo (Greek: &#941;&#956;&#946;&#961;&#965;&#959;&#957;) is a diploid eukaryote in its earliest stage of development.

Description
In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote that has all the DNA of two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. The term embryo refers to the early stages of this development, after the zygote has divided at least once, but before the process has completed to produce a new individual.

Information

 * Plants: In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem (see hypocotyl), and root (see radicle), as well as one or more cotyledons. Once the embryo begins to germinate &mdash; grow out from the seed &mdash; it is called a seedling.


 * Animals: The embryo of vertebrates is defined as the organism between the first division of the zygote (a fertilized ovum) until it becomes a fetus. An embryo is called a fetus at a more advanced stage of development and up until birth or hatching. In humans, this is from the eighth week of gestation.


 * Stages: morula-> blastula->gastrula.

Growth of the Human Embryo
Week 1-4 After conception, the embryo will begin to "search" for a place to attach to the woman's uterus. When it finds one and plants itself there, the connections between the mother and the embryo will begin to form, including the umbilical cord.

Week 5-8 Chemicals produced by the embryo stop the mother's menstruational cycle. The brain begins to develope, and the heart will begin to beat. Stubs begin to be visible where arms and legs will grow later. All the main organs begin to grow. The embryo's blood type becomes apparent. Embryo is capable of motion, and the eyes begin to form. Most organs have developed or have begun developing. At the end of the 8th week, the embryoic stage is over, and the fetal stage begins.

External link

 * Chart of human development
 * [A Comparative Embryology Gallery]

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