1. Prenatal Development Information in this presentation is taken from UCCP Content

2. 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

3. 1 st – 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.

4. 2 nd – 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.

5. 3 rd – 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.

6. 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)