Chapter 11: Human Development Across the Life Span
1. Outline the major events of the three phases of prenatal development.
Development begins with conception, which occurs when fertilization creates a zygote, a one-celled organism
formed by the union of a sperm and an egg. The prenatal period extends from conception to birth, usually
encompassing nine months fo pregnancy. The GERMINAL stage is the first stage of prenatal development,
encompassing the first two weeks after conception. One in five pregnancies occur without the woman ever
knowing that conception occurred. The placenta is a structure that allows oxygen and nutrients to pass into the
fetus from the mother’s bloodstream and bodily wastes to pass out of the mother. The EMBRYONIC stage is the
second stage, lasting from two weeks until the end of the second month. Most vital organs and body systems begin
to form. Heart, spine, and brain structures emerge. All basic physiological structures are being formed, very
vulnerable period. The FETAL stage is the third stage lasting from two months through birth. Rapid body growth
and physical movements occur as skeletal structure, muscles, and organs continue to grow and form. During the
final three months of the prenatal period, brain cells briskly multiply. A layer of fat is deposited under the skin to
provide insulation, and the respiratory and digestive systems mature. Sometime between 22 and 26 weeks, the
fetus reaches the age of viability-the age at which a baby can survive in the event of a premature birth.
2. Summarize the impact of environmental factors on prenatal development.
Severe maternal malnutrition increases the risk of birth complications and neurological defects for the newborn,
and prenatal malnutrition may have negative effects decades after the child’s birth, such as schizophrenia and
other psychiatric disorders, as well as risk of heart disease and diabetes. Virtually all recreational drugs can be
harmful, especially sedatives, narcotics, and cocaine. Heroin can cause addiction to narcotics and may lead to
early death due to premature birth, birth defects, etc. Cocaine is associated with increased risks of birth
complications. Drugs prescribed for legitimate medical reasons can cause problems as well, as well as over-the-
counter drugs. Impact of drugs depends on dose, drug, and phase of prenatal development. Fetal alcohol syndrome
is a collection of congential problems associated with excessive alcohol use during pregnancy, leading to a small
head, heart defects, irritability, hyperactivity, and delayed motor and mental development, as well as mental
retardation, depression, suicide, and criminal behavior.Tobacco can reduce the flow of nutrients and oxygen to the
fetus, causing miscarriage, stillbirth, prematurity, and greatly increasing the risk of sudden infant death syndrome.
The fetus is largely defenseless against infections because its immune system matures relatively lare in the