Embryo

An embryo is the initial stage of development for a <a href="/facts/Multicellular_organism/rk8QBF7o">multicellular organism</a>. In <a href="/facts/Organism/j8JkL09u">organisms</a> that <a href="/facts/Sexual_reproduction/hmsXy53s">reproduce sexually</a>, <a href="/facts/Embryonic_development/1lFY4EoW">embryonic development</a> is the part of the life cycle that begins just after <a href="/facts/Fertilization/g8u3UKzF">fertilization</a> of the female <a href="/facts/Egg_cell/gJyW3W3W">egg cell</a> by the male <a href="/facts/Sperm_cell/RCxpXygQ">sperm cell</a>. The resulting fusion of these two cells produces a single-celled <a href="/facts/Zygote/mSu2xMWA">zygote</a> that undergoes many <a href="/facts/Cleavage_(embryo)/v0osHpJC">cell divisions</a> that produce <a href="/facts/Cell_(biology)/bLM9UQvy">cells</a> known as <a href="/facts/Blastomere/xpThgJVq">blastomeres</a>. The blastomeres (4-cell stage) are arranged as a solid ball that when reaching a certain size, called a <a href="/facts/Cleavage_(embryo)/v0osHpJC">morula</a>, (16-cell stage) takes in fluid to <a href="/facts/Cavitation_(embryology)/ry1H6kdW">create a cavity</a> called a <a href="/facts/Blastocoel/QQUUs93N">blastocoel</a>. The structure is then termed a <a href="/facts/Blastula/sJVSBmbH">blastula</a>, or a <a href="/facts/Blastocyst/WkRkxdzc">blastocyst</a> in <a href="/facts/Mammal/phSwTzBo">mammals</a>.
The mammalian blastocyst <a href="/facts/Zona_hatching/t1C3l6qs">hatches</a> before <a href="/facts/Implantation_(embryology)/k6XJfNMv">implantating</a> into the <a href="/facts/Endometrial/LcesXIXm">endometrial</a> lining of the <a href="/facts/Womb/LIrApMXs">womb</a>. Once implanted the embryo will continue its development through the next stages of <a href="/facts/Gastrulation/kN8X10mK">gastrulation</a>, <a href="/facts/Neurulation/awsFwAGt">neurulation</a>, and <a href="/facts/Organogenesis/Wzd0g1al">organogenesis</a>. Gastrulation is the formation of the three <a href="/facts/Germ_layer/eSUTuH7F">germ layers</a> that will form all of the different parts of the body. Neurulation forms the <a href="/facts/Nervous_system/CDxRKU2U">nervous system</a>, and organogenesis is the development of all the various tissues and organs of the body.
A <a href="/facts/Human_embryonic_development/JeVmIcT0">newly developing human</a> is typically referred to as an embryo until the ninth week after conception, when it is then referred to as a <a href="/facts/Fetus/evocHd0Y">fetus</a>. In other multicellular organisms, the word "embryo" can be used more broadly to any early developmental or life cycle stage prior to <a href="/facts/Birth/1SSk6gMD">birth</a> or <a href="/facts/Hatchling/MWTsu0ja">hatching</a>.

Embryo open-in-new

Embryo