Birth and development. Beginning of life cycle. Fertilization- Only one sperm fertilizes the egg. In the first week the egg undergoes many cell divisions and travels to the uterus. Zygote- United sperm and egg
The Blastocyst- 5 days after fertilization the embryo reaches the uterus where it floats free for a few days. At this time made up of 50-100 cells. The structure is now called a blastocyst and is a sphere of cells surrounding a hallow center.
Mother: Changing hormone levels tell the body to produce milk and cause the uterus to gradually shrink to normal size.
Premature birth- Delivery before 37 weeks. The baby is not fully developed and complications can arise.