Human Growth and Development

Zygote When a sperm carrying half the necessary DNA combines with an egg containing half the necessary DNA combine a zygote forms. A zygote contains all of the genetic information (DNA) necessary to become a child. The zygote undergoes mitosis until a ball of cells is formed.

Blastocyst In a few days a ball consisting of an inner group of cells and an outer shell is formed. This ball is called a blastocyst. The inner cells will become the fetus. The outer shell will become the membranes that nourish and protect the fetus.

Embyro The cells begin to differentiate (take on specific functions – types of cells that make up a human being) some form blood cells, others form nerve, bone, etc. These first few weeks are when a developing child is most at risk from what the mother takes into her system.

Embryo 1st week Embryo has moved from the fallopian tubes to the uterus where it attaches to the uterine wall. The placenta and umbilical cord will grow and connect the fetus to the mother. This will be the fetus’s only source of food, water, and oxygen.

Embryo First 3 to 5 weeks The heart, brain and spinal cord have already begun to develop.

After about 8 weeks the embryo is considered a fetus Most of the organs and main body parts have begun to develop and can be clearly seen here.

10 to 32 weeks 10 weeks 12 weeks 32 weeks Eyes aren’t complete until about 24 weeks.

Were you paying attention? What is a fertilized egg called? ________________ In a ________________ the inner cells become the ____________ the outer layer of cells become the membranes (placenta/amniotic sack) that nourish and protect the fetus. At how many weeks is the embryo considered a fetus? _________ Where are eggs usually fertilized? ___________________

What two things connect the fetus and the mother providing food, water, and oxygen to the fetus? ________________ This is a thin but tough bag that surrounds the fetus protecting it and holding in the fluid that surrounds the fetus. ________________ When do the eyes finish forming? ___________