1. Pregnancy Pregnancy occurs once the zygote implants into the uterine wall The zygote keeps growing by mitosis, eventually the cells differentiate and form an embryo with a placenta Mother provides food, oxygen and waste disposal for the growing baby PLACENTA: location where nutrients and oxygen diffuse into the embryo’s blood vessels from the mother’s blood and wastes diffuse out –Mother’s blood and baby’s blood NEVER mixes AMNION: fluid filled sac that surrounds the membrane; fluid protects baby from temperature changes and bumps, allows for movement UMBILICAL CORD: blood vessel that runs between the the placenta and attaches to the fetus at the bellybutton

2. Identical twins often share the same placenta, usually have separate amniotic sacs, and always have their own umbilical cords Nonidentical twins are the result of two different eggs being fertilized so they have separate placentas, amniotic sacs, and umbilical cords. The average pregnancy is 38 weeks long, the average baby 7 1/2 lbs, average weight gain in healthy pregnancy is 15-35 pounds First trimester critical to proper development of organs, especially the brain Many drugs including alcohol can pass through the mother’s bloodstream into the developing infants and may cause deformities or developmental difficulties

3. Birth Dramatic changes in hormone levels trigger birth LABOUR: Uterus begins to contract and birth canal opens Cervix thins and dilates (opens), once it reaches 10 cm the baby may begin to come out

4. Embryonic Tissue Layers

5. 6 weeks