Fertilization to Birth

1. Fertilization to Birth 21.2

2. Fertilization • Sperm is deposited into the vagina • Travels through the uterus, to the oviducts • Egg fertilized in oviduct • Zygote formed • A Biochemical Event • Only one sperm will fertilize the egg • Sperm releases an enzyme to disrupt the egg membrane • Response of the Egg • Egg releases chemical secretions that prevent penetration by other sperm • Nucleus of sperm fuses with nucleus of egg • Zygote undergoes mitosis

3. Development before Birth • About seven days to travel to uterus • Attaches to uterine wall • Pregnancy – 9 month time period were fertilized egg will develop into baby • The Embryo • Embryo – first two months of pregnancy • Nutrients from wall of uterus are received by the embryo from villi • Blood vessels develop from the villi and form placenta • Umbilical cord is attached to embryo’s navel and connects with the placenta • Amniotic sac – clear amniotic fluid, that cushions against blows and can store nutrients and wastes • Three months – all major organs form

4. The Fetus • Fetus – developing baby after first two months • Third month – 8cm – 10cm long, heartbeat heard, feel movements • Fourth month – determine gender of fetus • Seventh month – 30 to 38cm • Ninth month – shifted to head down position, 50cm in length • Multiple Births • Fraternal twins – two eggs, two sperm. • Do not all look alike. • Can be one boy, one girl • Identical twins – one egg, one sperm. • Splits shortly after fertilization. • Must be both girls or both boys.