Editing Embryo (section)

{{short description|Multicellular diploid eukaryote in its earliest stage of development}}
{{Other uses}}
{{Infobox embryology
| Name        = Embryo
| Latin       =
| Image      = Embryo 7 weeks after conception.jpg
| Caption    = A [[human]] embryo seven weeks after [[conception (biology)|conception]] (nine weeks [[Gestational age (obstetrics)|gestational age]])
}}

An '''embryo''' is the initial stage of development for a [[multicellular organism]]. In [[organism]]s that [[Sexual reproduction|reproduce sexually]], [[embryonic development]] is the part of the life cycle that begins just after [[fertilization]] of the female [[egg cell]] by the male [[sperm cell]]. The resulting fusion of these two cells produces a single-celled [[zygote]] that undergoes many [[Cleavage (embryo)|cell divisions]] that produce [[Cell (biology)|cells]] known as [[blastomere]]s. The blastomeres (4-cell stage) are arranged as a solid ball that when reaching a certain size, called a [[Cleavage (embryo)|morula]], (16-cell stage) takes in fluid to [[Cavitation (embryology)|create a cavity]] called a [[blastocoel]]. The structure is then termed a [[blastula]], or a [[blastocyst]] in [[mammal]]s.

The mammalian blastocyst [[Zona hatching|hatches]] before [[Implantation (embryology)|implantating]] into the [[endometrial]] lining of the [[womb]]. Once implanted the embryo will continue its development through the next stages of [[gastrulation]], [[neurulation]], and [[organogenesis]]. Gastrulation is the formation of the three [[germ layer]]s that will form all of the different parts of the body. Neurulation forms the [[nervous system]], and organogenesis is the development of all the various tissues and organs of the body.

A [[Human embryonic development|newly developing human]] is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a [[fetus]]. In other multicellular organisms, the word "embryo" can be used more broadly to any early developmental or life cycle stage prior to [[birth]] or [[Hatchling|hatching]].