Chapter 18: Growth and Development

Embryonic development fertilization: the fusion of male and female gametes to form a zygote.

Once the egg joins with the sperm, it makes a zygote and then begins to divide The zygote now goes through MITOSIS as it travels down the fallopian tubes on its way to the uterus

This mitotic cell division of the zygote is called cleavage

Process of cleavage The zygote divides by mitosis into 2 identical cells These 2 cells divide into 4 cells

Those 4 divide into 8 cells Those 8 divide into 16 cells and forms a solid ball of cells called the morula

As the cells continue to divide, the center of the ball becomes hollow This hollow ball stage is called the blastula

By the end of the six days the zygote is called a blastocyst

The blastula stage is followed by the formation of the gastrula During the formation of the gastrula, one side of the blastula pushes inward to form the 3 germ layers

The 3 germ Layers This results in the formation of a second inner layer of cells called the endoderm The outer cell layer is called the ectoderm A third cell layer forms between called the mesoderm

The gastrula will eventually differentiate to form the specialized cells. Differentiation means that the cells will develop specific jobs and develop into specific tissues in the maturing organism.

In an embryo, the formation of many types of tissues and organs occur as a result of differentiation

After the 3 germ layers have formed, the nervous system begins to develop The ectoderm cells along the back of the embryo begin to grow into a long hollow tube called the neural tube

The neural tube becomes wider at one end The wider part develops into the brain The long and narrow end develops into the spinal cord

There are 2 main groups of cells in the blastocyst 1. one group will become the embryo 2.The outer layer of cells is called the trophoblast

Functions of the trophoblast Once inside the uterus it attaches to the uterus lining It secretes the hormone HCG which tell the corpus luteum to keep making progesterone so that menstruation will stop

it’s the layer of cells around the embryo that connects the embryo to the lining of the uterus[implantation]

After implantation, a membrane on the outside called the chorion forms It connects to the uterine wall

A membrane on the inside called the amnion forms the amniotic sac The amniotic sac contains the amniotic fluid that surrounds and protects the embryo

What is the purpose of the amniotic fluid? it helps keep the baby warm provides lubrication that keeps body parts from growing together helps the baby's lungs develop lets the baby move easily so he can exercise his muscles and strengthen his bones before he’s born. it acts like a liquid shock absorber for the baby by distributing any force that may push on the mother’s uterus

The chorion begins to grow into the mother’s tissue Blood vessels develop in this fetal tissue

At the same time, tissue with its own blood vessel grow from the uterine lining of the mother, this structure is called the placenta

What is the function of the placenta? Allows nutrients and oxygen to diffuse from the mother to the baby It also helps to protect the baby from infections because it keeps the mother's blood and baby's blood separate by acting as a filter

The umbilical cord connects the placenta to the baby

Danger signs during pregnancy

Assisted reproductive technology methods Test to detect birth defects during pregnancy Stages of labor and childbirth Pain relief during childbirth

Stages of a developing baby Stage 1: zygote day 1 – day 7 Stage 2 embryo day 8 – week 8 Stage 3 fetus week 9 – week 40

4 stages of the human life cycle 1. Infancy/toddler 2. childhood 3. adolescence/teenager 4. adulthood

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