Chapter 11 - Prenatal Development

Question 1

Define prenatal period

Answer 1

The prenatal period extends from conception to birth, usually encompassing nine months of pregnancy.

Question 2

The prenatal period is divided into three phases:

Answer 2

1) the germinal stage (first two weeks)
2) the embryonic stage (first two weeks and two months)
3) the fetal stage (two months to birth)

Question 3

germinal stage

Answer 3

The germinal stage is the first phase of prenatal development, encompassing the first two weeks after conception.

events:
-begins when a zygote is created through fertilization.
-within 36 hours, rapid cell division begins and the zygote becomes a microscopic mass of multiplying cells.
-this mass of cells slowly migrates along the mother’s fallopian tube to the uterine cavity.
-on about the seventh day, the cell mass begins to implant itself in the uterine wall.

Question 4

Define placenta

Answer 4

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 to the mother.

Question 5

embryonic stage

Answer 5

the embryonic stage is the second stage of prenatal development, lasting from two weeks until the end of the second month.

events:
-most of the vital organs and bodily systems begin to form in the developing organism, which is now called an embryo.
-structures such as the heart, spine, and brain emerge gradually as cell division becomes more specialized.
- although the embryo is typically only about 2.5 cm long at the end of this stage, its arms, legs, hands, feet, fingers, toes, eyes, and ears are already discernible.

**note: If anything interferes with normal development during this phase, the effects can be devastating. most miscarriages occur during this period, and most major structural birth defects result from problems during the embryonic stage.

Question 6

fetal stage

Answer 6

the fetal stage is the third stage of prenatal development, lasting from two months through birth.

events:
-the developing organism has forming bones and muscles, and is now considered a fetus, capable of physical movements as skeletal structures harden.
-organs formed in the embryonic stage continue to grow and gradually begin to function.
-sex organs start to develop during the third month.

during the final 3 months of the prenatal period:
-brain cells multiply rapidly.
-a layer of fat is deposited under the skin to provide insulation.
-respiratory and digestive systems mature.

Question 7

threshold of viability

Answer 7

sometime between 23 weeks and 25 weeks, the fetus reaches the threshold of viability - the age at which a baby can survive in the event of a premature birth.

**at 23 weeks, the probability of survival is still slim (about 24%), but it climbs rapidly to around a 72% survival rate at 25 weeks. many premature infants born near the threshold of viability go on to experience a wide range of developmental problems.

Question 8

can environmental factors affect the developing organism in the womb?

Answer 8

yes, events in the external environment can affect it indirectly through the mother.

Question 9

what environmental factors can affect the developing organism?

Answer 9

because the developing organism and its mother are linked through the placenta, a mother’s eating habits, drug use, and physical health, among other things, can affect prenatal development and have long-term health consequences.

Question 10

define teratogens

Answer 10

teratogens are any external agents, such as drugs or viruses, that can harm an embryo or fetus.

Question 11

maternal nutrition

Question 12

maternal drug and alcohol use