Fertilization and Development

Ovulation is when the egg is released from the follicle.

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.