DEVELOPMENT OF THE ZYGOTE
Fuelled by nutrients from the ovum, the zygote divides rapidly to form smaller cells – the embryo remains the same size.
After 3 divisions, there are 8 totipotent stem cells – each could form a total human being. After 5 days, a blastocyst (a hollow ball of cells) is formed:
- the outer cell layer forms the placenta
- the inner are pluripotent embryonic stem cells (each can form most, but not all cell types)
As the embryo develops, cells differentiate and become more specialised.
Most lose the ability to develop into a wide range of cell types, but some don’t: they are multipotent stem cells.