Prenatal Development & Teratogens

What is conception?

When the sperm and egg unite in the fallopian tube to form a zygote, marking the beginning of pregnancy.

What happens when one sperm breached the egg membrane?

It triggers a chemical reaction that forms a hard shell, not allowing others to get in

How is a zygote created?

A fertilized egg, that occurs when the sperm penetrates an egg and they come together to initiate prenatal development.

What is a zygote made up?

This cell has the full complement of genetic material from both parents, including half of the chromosomes from each. 23 from the sperm, 23 from the egg, thus combining into 46 chromosomes.

What are the three stages of prenatal development?

1) Germinal Stage

2) Embryonic Stage

3) Fetal Stage

How long does the germinal stage last?

From conception to implantation (to the uterine wall), about 2 weeks

What happens in the Germinal Stage?

Rapid cell division occurs but there is no increase in mass.

By the end of this rapid cell division, a blastocyst occurs

What is a blastocyst?

A ball of cells that has an outer layer that develops into things that help support and nourish the baby as it grows (amniotic sac, umbilical cord, and the placenta).

It also has an inner mass, that develops into the baby and is filled with fluid.

Forms four days after conception and is what embeds into the uterine wall

It' can’t grow in the beginning because it’s not connected to the mother

What is the hatching blastocyst and implantation?

6 days after conception, the egg hatches from the hard shell and embeds into the uterine wall

IMPLANTATION: A hatched egg that attaches to the uterine wall and begins to receive nutrients

How long is the Embryonic Stage?

Implantation to 8th week post-conception (10 weeks)

What forms during the Embryonic Stage?

Major organ systems form

• The heart begins to beat

• Eyes, ears, nose, and mouth begin to form

• Excretory system (kidney and liver)

• Teeth buds

How do teratogens play a role during the Embryonic Stage?

This is a sensitive period-vulnerable to teratogens

• Key in development

• Exposure to teratogens during this stage can damage prenatal development negatively

What support systems form that help nourish the baby?

• Amniotic sac: Protects the fetus within the uterus. It acts as a shock absorber and helps the baby regulate its temperature

• Placenta: Acts as a filter between the mother’s bloodstream and the baby’s. It exchanges nutrients, waste, and CO2 and oxygen

• Umbilical cord: Connects the baby to the placenta.

How long is the Fetal Stage?

8th week through birth

What is time til viability vs. Full term?

Time till viability: A baby is considered viable (meaning it can live after being born) at roughly about 24 weeks (end of second trimester)

Full-term: If you give birth between 39-40 weeks and 6 days after your last period

More information about the Fetal Stage?

• By the 1st trimester, all the major organ systems, finger, toes, and eyes are formed

• Can see the sex of the baby visually (2nd trimester)

• Around the 7th month, the fetus’s turns upside down to prepare for birth

• First fetal movements are detected

• Head develops first

What is a teratogen?

Any environmental agent that can harm an embryo/fetus that can damage prenatal development

What factors influence the severity of the damage and the type of defect that occurs?

• Dose: The greater the dose, the greater the effect

• Genetic susceptibility: Based upon the genotype of the pregnant mother and the fetus, some fetuses are more sensitive to certain teratogens than others

• Age of exposure: Depending on the age of the fetus, teratogens do more damage during the embryonic stage of prenatal development

How do teratogens affect each stage?

• Germinal stage: The zygote/blastocyst is not generally susceptible to environmental teratogens since it’s not connected to the mother

• Embryonic stage: The most sensitive period of prenatal development, since every major organ is under development

• Fetal stage: Once is fetus is formed and all the basic organs are in place, damage from teratogens is likely to be less severe.