We have now entered the embryonic period of development, which lasts for eight weeks. All along this period the zygote is referred to as the embryo.
As the Zygote gets implanted and becomes the Embryo, the blastocyst will have two layers of cells.
The inner layer of cells is called the Endoderm that eventually develops into the digestive and the respiratory systems.
The outer layer is divided into two parts: the Ectoderm and Mesoderm. The Ectoderm will develop into the nervous system, the sensory receptors (eyes, ears, nose, etc.) and the skin including nails and hair, while the Mesoderm will become the bones, muscles, excretory, circulatory and reproductive systems.
The next stage of development, from month two onwards until the birth of the child, is the fetal period of development. To summarize the life of a child begins, when an egg, previously released from one of the two ovaries, merges itself with just one of the hundreds of millions of sperm cells supplied through the vagina by the male reproductive system. The fertilized egg then descends to the wall of the uterus, where it implants itself to begin the period of gestation (Fig 1.10).
1.2.5 Fetal life support systems
The further development of the Fetus continues with vital contribution from many life support systems such as the Amnion, Umbilical cord and the Placenta.