Outline the stages of prenatal development and discuss the environmental risks that may impact upon the developing fetus Flashcards
How would you structure an essay outlining the stages of prenatal development and discussing the environmental risks that may impact on the developing fetus?
- Introduce structure
- Stages of prenatal developments (introduce, zygote, embryo, fetus)
- Teratogens (introduce, diseases, drugs, environmental hazards)
- conclusion
How many stages is prenatal development divided into?
3
What is the first stage of prenatal development called? How long does it last?
The period of the zygote
Lasts from conception through implantation - 10 - 14 days
What is the second stage of prenatal development called? how long does it last? what mainly happens during this phase?
- Period of the embryo
- beginning of 3rd week - end of 8th week
- Virtually all major organs formed and heart begins to beat
What is the 3rd stage of prenatal development called? how long does it last? what mainly happens during this phase?
- the period of the fetus
- lasts from the 9th week of pregnancy until the baby is born.
- During this phase all the major organ systems begin to function, and the developing organism grows rapidly.
What happens in the first week? (period of zygote - 3 points)
- In the first week, as the fertilized ovum, or zygote, moves down the fallopian tube toward the uterus, it divides by mitosis into two cells
- These two cells and all the resulting cells continue to divide, forming a ball-like structure, or blastocyst, that will contain 60 to 80 cells within 4 days of conception.
- Cell differentiation has already begun, the inner layer of the blastocyst will become the embryo, and the outer layer of cells will develop into tissues that protect and nourish the embryo.
What happens in the second week?
In the second week the blastocyst implans into the uterine wall; and structures that nourish and protect the organism, such as: amnion, chorion, yolk sac, placenta, and umbilical cord, begin to form.
What structures that nourish the organism begin to form in the second week? (p of zygote)
Amnion chorion yolk sac placenta umbilical cord
How long does period of embryo last?
The period of the embryo lasts from implantation (roughly the third week) through the 8th week of pregnancy.
What is happening in the third week? (period of the embryo)
By the 3rd week the embryonic disk is rapidly differentiating into three cell layers: ectoderm, mesoderm, and endoderm
What is the outer layer of the embryonic disk called? What does it become?
Ectoderm
It will becomes the nervous system, skin and hair
What is the middle layer of the embryonic disk called? What does it become?
Mesoderm
It will become the muscles, bones, and circulatory system
What is the inner layer of the embryonic disk called? What does it become?
Endoderm
It will become the digestive system, lungs, urinary tract, and other vital organs such as the pancreas and liver
What happens in weeks 3-4 (period of embryo - 3 points)
- Embryo grows to .25 inches
- Brain, spinal cord and heart form
3. as do the rudimentary structures that will becomes the: eyes ears nose mouth limbs
What happens in weeks 5-8? (period of embryo - 5 points)
- Grows to 1 inch
- External body structures form
- Internal organs form
- Embryo now produces its own blood
- Embryo can now move
How long does the period of the fetus last?
The last 7 months of pregnancy
The last X months of pregnancy, or the period of the fetus, is a period of rapid [blank] and [blank] of all organ systems
7
growth
refinement
Broadly what happens during the period of the fetus? (2 sentences)
- all major organ systems begin to function and the fetus begins to move, sense, and behave (although not intentionally).
- individuality emerges as different fetuses develop unique characteristics, such as different patterns of movement and different facial expressions
What happens in weeks 9-12 of the period of the fetus? (3 points)
- The fetus grows to 3 inches
- Rapid growth and interconnections of all organ systems permits new competencies:
- body and limb movement
- swallowing
- digestion of nutrients
- urination - External genitalia form now too
What happens in weeks 13-24 of the period of the fetus? (5 points)
- Grows to 14-15 inches
- Fetal movements felt by mother
- Fetal heartbeat can be heard
- Fetus is covered by vernix to prevent chapping
- Reacts to bright lights and sounds
What happens in weeks 25-38 of the period of the fetus? (6 points)
- Grows to between 19-21 inches
- Weighs 7-8lbs as organs mature in preparation for birth
- Reaches age of viability
- Becomes predictable in its sleep cycles and motor activity
- Layer of fat develops under the skin
- Activity becomes less frequent as the baby sleeps more in the last 2 weeks before birth
How many sub-sections can you divide the period of the fetus into? (weeks)
3
9-12
13-24
25-38
What % of newborn infants follow the ‘normal’ pattern of prenatal development?
95%
What does the term teratogen refer to?
The term teratogen refers to any disease, drug, or other environmental agent that can harm a developing embryo or fetus by causing physical deformities, severely retarded growth, blindness, brain damage, or even death (Fifer, 2005).
The list of known and suspected teratogens has grown very long over the years; however…
it is important to emphasise that 95% of newborn babies are perfectly normal, and that many of those born with defects have mild, temporary, or reversible problems (Gosden, Nicolaides, & Whitting, 1994).
each major organ system or body part has a sensitive period when it is most susceptible to teratogenic agents - when is this usually?
the time when that particular part of the body is forming (most organs and body parts are rapidly forming during the period of the embryo)
Once an organ or body part is fully formed, it becomes less susceptible to damage. However…
some organ systems (particularly the eyes, genitals and nervous system) can be damaged throughout pregnancy.
Further, in research looking at birth defects and drugs in pregnancy, Heinonen and colleagues (1977) concluded that …
that many of the birth defects found among the 50,282 children in their sample were ‘anytime malformations’ - problems that could have been caused by teratogens at any point during the 9 month prenatal period
What are the three kinds of teratogens we are going to look at?
diseases
drugs,
environmental teratogens.
Some disease agents are capable of crossing the X and doing much more damage to a developing embryo or fetus than to the pregnant woman herself
placental barrier
Some disease agents are capable of crossing the placental barrier and doing much more damage to a developing embryo or fetus than to the pregnant woman herself. This makes sense when we consider that… (2 points)
an embryo or fetus has an immature immune system that cannot produce enough antibodies to combat infections effectively, and that the fetal environment may react differently to infections than the pregnant woman’s immune system does.
No infections are more common, and few are more hazardous to the fetus than…
sexually transmitted infections.
According to one estimate, as many as X million adolescents and adults in the United States either have or have had a sexually transmitted disease (STD) that is capable of producing serious birth defects. Who estimated this?
32
Cates, 1995
Three of these diseases: X, Y, and Z - are particularly hazardous.
- Syphilis
- Genital Herpes
- Acquired Immunodeficiency Syndrom
If untreated, what can syphilis cause?
- miscarriage
2. Serious defects including eye, ear, bone, heart, or brain damage
What did Artistotle note in relation to drunken mothers? Says who?
That they had ‘feeble-minded babies’ (Abel, 1981)
now we know that alcohol affects the development of the fetus directly and indirectly by…
compromising the function of the placenta
In 1973 X and colleagues described a Y that affects many children of alcoholic mothers.
Kenneth Jones
Fetal Alcohol Syndrome
What are the most noticeable characteristics of fetal alcohol syndrome?
- Microcephaly
2. Malformations of the heart, limbs, joints and face
FAS babies are likely to display what 4 things?
- excessive irritability
- hyperactivity
- seizures
- tremors
FAS babies are also X and Y than normal, and their physical growth lags behind that of normal age-mates.
smaller
lighter
Finally, the majority of the X in Y babies born with FAS score well below average in intelligence throughout childhood and adolescence, and more than Z% of them display [blank]
3 in 1000
90%
major adjustment problems as adolescents and young adults
It is not just recreational drugs that have teratogenic effects -
some of the most commonly used over-the-counter-drugs have suspected negative effects on the developing fetus.
Heavy use of aspirin, for example, has been linked to …
fetal growth retardation, poor motor control and even infant death (Barr et al., 1990);
the use of ibuprofren in the third trimester increases the risk of…
a prolonged delivery and pulmonary hypertension in newborns (Chomitz, Cheung and Lieberman, 2000).
What do environmental hazards as teratogens include?
chemicals in the environment that the pregnant woman cannot control and may not even be aware of, as well as some that she can regulate.
What is probably the most well known environmental hazard for the developing fetus?
Radiation
How did the harmful effects of radiation to the developing fetus come to light?
following the atomic blasts of 1945 in Japan
What happened to preganant women within half a mile of the 1945 atomic blast in Japan?
Not one gave birth to a live child
What happened to preganant women within 1.25 miles of the 1945 atomic blast in Japan?
75% of the pregnant women who were within 1.25 miles of the blasts had seriously disabled children who soon died, and those who did survive were often mentally retarded (Apgar & Beck, 1974).
Less understood environmental hazards that pregnant women come in contact with on a regular basis include what four things? Why are they thought to have teratogenic effects?
food additives, artificial sweetners, pesticides, and cosmetic products,
some of which are known to have teratogenic effects in animals.
Unfortunately, the risks associated with a large number of these common chemical additives and treatments ….
remains to be determined.
To conclude…. (2 sentences)
In answering this question we first introduced the three stages of prenatal development, before exploring environmental risks that may impact on fetal development. The environmental risks we explored were: diseases, drugs and environmental hazards.
