Describe the developmental stages of human embryo after fertilization.
- During fertilization, chromosomes of the ovum and the chromosomes of the sperm make up into pairs and the resulting cell is called zygote.
- Fertilization takes place in the oviduct or fallopian tube.
- The zygote which is diploid travels down the fallopian tube. As it moves it undergoes several mitotic divisions forming the embryonic stage called blastocyst.
- Blastocyst moves towards the wall of the uterus and finally gets attached and embedded in the wall of the uterus. This is called implantation.
- The growing embryo forms two membranes chorion and Amnion.
- Chorion establishes connection with the walls of the uterus and helps in the supply of nutrients to the embryo and removal of wastes from the embryo.
- Amnion forms a sac like structure around the embryo. The space between the amnion and embryo is filled with a fluid called amniofic fluid.
- Amnion and amniotic fluid give protection to the embryo against minor mechanical injury.
- Placenta is a tissue formed by the cells from the embryo and the mother. It is formed around 12 weeks of pregnancy.
- Placenta nourishes the growing embryo.
- A tough cord called umbilical cord is also formed by the embryo which is connected to the walls of the uterus through the placenta.
- From 3 months of pregnancy, the embryo is called foetus.
- Pregnancy lasts on an average 9 months or 280 days. This period is called gestation period.