The Formation and Development of a New Individual
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After ovulation, the ovum may be fertilized.
Embryonic Development
Embryonic development lasts approximately nine months, from fertilization to implantation.
Fertilization
Fertilization is the process in which a spermatozoon and an ovum join together to create a zygote in the Fallopian tubes.
Cleavage
The first divisions of the zygote, known as cleavage, occur while it travels down to the uterus. This process turns it from a zygote into an embryo.
Implantation
When the embryo arrives in the uterus, it embeds in the endometrium.
The Formation of the Placenta and the Amniotic Sac
Once the embryo is implanted, two structures are formed to protect it and provide it with nourishment. The placenta is an organ which links the embryo to its mother through the umbilical cord to exchange nutrients, oxygen, waste, etc. The amniotic sac is a bag filled with amniotic fluid.
The Complete Development of the Embryo
In the first trimester, the majority of the embryo's organs have been formed. From week eight, it is known as a fetus. In the second trimester, the fetus's skeleton ossifies and it also starts to move. In the third trimester, the fetus grows, puts on weight, and its organs and systems finish developing.
Birth
Birth is the process in which the new individual is expelled from its mother's body. It occurs in three phases:
- Dilation of the cervix, which causes it to widen
- Expulsion of the fetus by means of contractions of the muscular walls of the uterus
- Afterbirth expulsion of the placenta and fetal membranes