Guide Note
An embryo is the early fetal development of complex living organisms. Embryos have similar characteristics across many species.
Fast Facts
- In humans, embryo development includes growth before 8th week1
- After the 8th week, the developing human is considered a fetus1
- Embryonic development includes major cell specialization and organ system development1
- Alcohol, drugs and radiation can cause problems with embryonic development1
Fertilization
Embryonic development begins with the fertilization of the ovum by a single sperm cell. With the fertilization, the two cells merge to create a new cell called a zygote. The zygote begins to divide until, after three or four days it becomes a morula, named so because of its mulberry shape.2
Implantation
The morula enters the uterus from one of the fallopian tubes and after another day or two the group of cells, now called a blastocyst, will implant itself into the uterine lining. The blastocyst produces human chorionic gonadotropin hormone which starts a hormone chain reaction that prevents menstruation.2
Cell Differentiation
After the 12th day, the blastocyst begins to differentiate, first into two separate groups, and then further into groups of cells that will develop into organ systems over the next two weeks. The embryo will develop from a small ball of cells into a tadpole-like organism. After the organ systems form, they begin to develop detail, with the heart and the brain dividing into sections and appendages forming visible fingers with webbing. At eight weeks past conception, the embryo is called a fetus.1 2
Safety
During embryonic development, critical growth is going on. To prevent damage to embryonic cell growth, WebMD suggests maternal refrain from alcohol, drugs and radiation, especially during the early weeks of pregnancy.1
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