Describe the embryonic development of a zygote up to its implantation in humans.

When ova and sperm fertilized, the embryo is created with constantly dividing cell called the blastocyst. The blastocyst composed of two groups of cells, inner and outer cells, filled with fluids. Zona pellucida protects the blastocyst during maturation. The outer cells create the placenta and surrounding tissues to support fetal development in the uterus. The inner cells of the blastocyst will become the different tissues and organs of the human body in later development stage. The cells within the blastocyst grow fast and go through many changes and convert into more functional cells. In humans, these changes happen during the first few days of development, before the implantation in the uterus. At this stage, the zona pellucida breaks and releases the blastocyst. The zygote moves through the Fallopian tubes towards the uterus and implants around day ten. As the blastocyst reaches the final stage in the implantation, it develops into an embryo. This is where the organs and external structures develop. After ten-twelve weeks of pregnancy, the embryo evolves into fetus the final stage of development.