Fertilization of the egg occurs in the fallopian tube During fertilization, sperm and egg join to become a zygote (fertilized egg). The zygote begins to undergo mitosis (cell division) and eventually becomes a ball of cells called a morula. The morula eventually becomes a blastocyst. The blastocyst travels down the fallopian tube and gets imbedded in the lining of the uterus. This is known as implantation. Pregnancy begins during implantation and not fertilization. Pregnancy is divided into three trimesters.
First Trimester Inner surface of the blastocyst becomes the embryo. Embryo develops three different layers that develop into different body systems –Ectoderm Nervous system, epidermis of skin –Mesoderm Muscles, skeleton, circulatory, excretory, reproductive –Endoderm Lining of respiratory and digestive tracts, liver and pancreas After eight weeks, the embryo is called a fetus. Organs begin to develop.
Placenta and Umbilical Cord The placenta is the connection between the mother and the fetus. The placenta allows the exchange of nutrients, gases and wastes between the mother and the fetus. The placenta and umbilical cord allow the fetus to eat, breathe and remove waste. The umbilical contains blood vessels. Materials are exchanged by diffusion. Maternal blood and fetal blood never mix.
Second Trimester Heart begins beating Skeleton begins forming Hair grows Wake and sleep Begins to move (kicks, sucks thumb) Eyes open
Third Trimester Can see light and dark Reacts to music and loud sounds Fat deposits under skin
Childbirth Occurs about nine months after fertilization. Hormones cause muscles to contract in the uterus and relax in the vagina. The cervix dilates (opens up) so baby can pass from uterus into vagina. Amniotic sac breaks and fluid comes out. This is known as the “water breaking”. Baby is squeezed out through the vagina.
After Childbirth A few minutes after the baby is born, the placenta, amnion and uterine lining are expelled from the woman. These structures are called “afterbirth.” Lungs expand (baby cries and breathes on its own) Umbilical cord is tied and cut Baby can now live on its own.