Chapter 4: Prenatal Development and BirthImportance:1. Hereditary endowment is fixed2. Favorable conditions in the

mother’s body3. Proportionally greater growth and

development takes place4. Influence of significant people

Major Phases of Prenatal DevelopmentScientific term used to describe baby-to-be

Major developments in each period

I. Germinal Period

Period of the Zygote

8-14 days or Weeks 1-2

Conception until implantation

Germinal Period

Germinal Period

Germinal Phase

Germinal Phase

Germinal Phase

Germinal Period

Germinal Period

Germinal Period

Germinal Period

Germinal Period

Implantation

Implantation

II. Period of the Embryo When zygote is completely embedded in the uterine wall

Body structures and internal organs develop

3 layers begin to form in the embryo:1. Ectoderm: hair, skin, nervous system2. Mesoderm: muscles, bones, circulatory

system3. Endoderm: digestive system and lungs

Period of the Embryo

Embryo rests in a sac called amnion amniotic fluid shock-absorbing protection; constant

temperatureChorion: 2nd membrane after about a month of development; helps form the placenta

Weeks 3-8

Period of the Embryo

3-week old: salamander8-week old: most of the organs found in a mature human are in place; visible eyes, jaw, arms and legs

About 1 inch long and weighs only a fraction of an ounce

Period of the Embryo

Period of the Embryo

Period of the Embryo

Period of the Embryo

Period of the Embryo

III. Period of the Fetus

Weeks 9-38 Much larger and bodily systems begin to work (respiration, digestion, vision)

By 22-28 weeks, most systems function well enough that a fetus has a chance to survive

age of viability

Period of the Fetus

Distinct baby-like lookMay still have trouble breathing and cannot regulate body temperature yet

Fetus starts to behave as movements become obvious

Begins to hear sounds, taste different flavors

Period of the Fetus: 3rd Month

Period of the Fetus: 4th Month

Period of the Fetus:5th Month

Period of the Fetus:6th Month

Period of the Fetus:7th Month

Period of the Fetus:8th Month

Period of the Fetus:9th Month

Changes in a pregnant woman’s body