Human embryogenesis is the process of
cell division and
cellular differentiation of the
embryo that occurs during the early stages of
development. In biological terms, human development entails growth from a one celled
zygote to an adult
human being.
Fertilisation occurs when the
sperm cell successfully enters and fuses with an
egg cell (
ovum). The genetic material of the sperm and egg then combine to form a single cell called a zygote and the germinal stage of
prenatal development commences. Embryogenesis covers the first eight weeks of development and at the beginning of the ninth week the embryo is termed a
fetus.
Human embryology is the study of this development during the first eight weeks after fertilisation. The normal period of
gestation (pregnancy) is nine months or 38 weeks. The germinal stage, refers to the time from fertilization, through the development of the early embryo until
implantation is completed in the
uterus. The germinal stage takes around 10 days.