Prenatal Development
Information in this presentation is taken from UCCP Content
Prenatal Development
From the moment of conception, human
development begins and can be
influenced by both biological and
environmental factors.
The prenatal period of development is the
period of development between
conception and birth.
There are 3 stages of prenatal development:
germinal, embryonic, and fetal
1st – Germinal Stage
3 Major Achievements
1) Rapid and differentiated cell division
2) Increased specialization of cells
3) Attachment of the umbilical cord to the
placenta.
This attachment (connection) allows the zygote
to receive nutrients from the mother, but it also
allows harmful agents, such as viruses or
drugs to enter the embryo. These harmful
agents are called teratogens.
2nd – Embryonic Stage
The embryonic stage begins with the implantation of the
zygote to the uterine wall, at which time it becomes an
embryo and ends when bones begin to form (2 – 8
weeks).
In the embryonic stage, the most important development is
the formation of the major organs, such as the heart,
lungs, liver, eyes and ears.
This is a critical time period in development because
once cell differentiation is complete it cannot be redone
at a later stage.
This stage is often thought of as the most critical period of
prenatal development because exposure to teratogens,
such as drugs, viruses and alcohol can negatively effect
the development of the vital organs that are forming.
This can result in major defects or malformations.
3rd – Fetal Stage
The fetal stage begins when the bones begin to ossify
(harden) and ends at birth (this stage lasts from 8 –
approximately 38 weeks).
Some of the major achievements of growth during this
phase include:
- the hardening of bones, ossification
- rapid growth in size (from 3 inches to app. 20 inches)
- hearing (begins at app. 5 months)
- sensitivity to light.
By 7 months, the fetus’ digestive and respiratory systems
are working and the fetus can survive outside the womb;
this is known as the age of viability.
Teratogens
Teratogens affect individuals differently.
How much harm they cause depends on 4 major
factors:
1) dose (how much of a drug is taken)
2) heredity – individuals differ in how a
particular dose or teratogen affects them
3) timing – when the embryo or fetus is
exposed.
4) sum total of dose, heredity and timing (it
can have a cumulative effect)