Unit 3.1: Prenatal development Flashcards
What can you divide pregnancy into?
three trimester periods
Do the trimesters of pregnancy correspond with the three main periods of development?
no
Which stages are there and what does each stage come with?
zygote, embryo and fetus
specific biological changes
Germinal period (duration)
first two weeks after conception
embryonic period(duration)
- to 8. week after conception
Fetal period (duration)
- week until birth
When and how does pregnancy begin?
at conception (fertilisation)
sperm cell penetrates wall of egg cell (ovum)
-> zygote
Where does the fertilisation process normally take place?
inside the Fallopian tube
How does the germinal period start and how long does it last?
with fertilisation
first 14 days
What happens between fertilisation and the implantation into the uterus?
duplication of cells via mitosis
-> until it forms a blastocyst (4-5 days after fertilisation)
-> differentiation of cells into trophoblast (shell) and embryoblast (nucleus)
What will happen with the trophoblast and embryoblast after implantation into the uterus?
trophoblast: structures responsible for nutrition and protection of the embryo
embryoblast: becomes embryo
How does the germinal period end?
blastocyst implanted in wall of uterus
Why does the blastocyst implant itself into the wall of the uterus?
to receive mother’s blood supply
How many zygotes don’t achieve implantation and thus die?
50-75%
When does the embryonic period begin and end?
after implantation (2 weeks) until 8th week
Amnion
becomes amniotic sac surrounding the embryo (fluid-filled)
-> shock absorber
-> maintains temperature
-> reduces weight and facilitates movement
Yolk sac
produces blood cells for embryo until it has its own supply
Allantois
becomes umbilical cord
Chorion
becomes lining of placenta
Placenta
semi-permeable membrane embedded in uterus
separates mother from embryo
What passes through the placenta?
oxygen
carbon dioxide
sugars
proteins
fats
What does the embryo receive from the mother via the umbilical cord?
Maternal blood carrying oxygen and nutrients
Why can we say that the placenta is the site of all metabolic transactions between mother and embryo?
Embry receives oxygenated blood from mother and removes carbon dioxide and metabolic waste via the placenta
What is the embryoblast?
embryonic disc
consists of 3 layers of cells that will form all tissues and organs
What does the ectoderm layer of the embryoblast become? (outer layer)
nervous system, skin and hair
What does the mesoderm layer of the embryoblast become? (middle layer)
muscles, bones and cardiovascular system
What does the endoderm layer of the embryoblast become? (inner layer)
digestive system, lungs, urinary tract and other internal organs
What does the neural tube develop from, how and when does that happen?
primitive streak in ectoderm folds into neural tube
third week post-fertilisation
What develops in the 4th week (before anything else)?
4th: head, eyes, nose, ears and mouth
What is another major step in the embryonic period, related to the cardiovascular system?
minuscule blood vessel begins to pulsate
-> will later become heart
What develops in the 5th week?
retina and lenses
arms and legs (with webbed fingers and toes)
What happens in the 7th week?
finger and toes separate
rudimentary skeleton formed
What does the rapid development of the brain in the 5th to 8th week allow the embryo to do?
contract muscles and make sporadic movements (not voluntary)
What happens by the end of the embryonic period regarding the embryos blood supply?
liver and spleen produce red blood cells
How tall and heavy is an average embryo by the end of the embryonic period?
2.5 cm
1 gram
When does the genital/gonal ridge appear?
7-8th week
What happens in the 9th week regarding the indifferent gonad?
separates into male or female sex organs
What does the differentiation of the indifferent gonad depend on?
genetic information and enzymatic processes
How will the embryo be male or female?
male: 23rd chromosome XY
-> Y- chromosome (SRY gene) triggers indifferent gonad to produce testes
female: no message sent
-> ovaries produced
How much does the brain increase in size from the 4th to 6th month and why does this happen?
6x
neurogenesis: mass production of neurones
synaptogenesis: formation of synapses
Which direction will the brain develop in?
proximo-distal
-> hindbrain, midbrain, forebrain
Why is brain development in the 4th to 6th months of the fetal period considered particularly crucial?
CNS begins to regulate vital body functions (e.g. breathing and sucking)
When does the fetus reach the age of viability and what does this milestone mean?
end of 6th month
possible to be born prematurely and survive
Why does each day in the uterus between the 7th and 9th months of pregnancy increase the probability of a healthy life with normal cognitive development?
increased maturation of neurological, respiratory and cardiovascular systems
-> mature CNS helps organs work in unison
Why is inhaling and exhaling amniotic fluid in the uterus incredibly important for the fetus?
strengthens the muscles necessary for breathing
How does the mother child relationship behave during the last 3 months?
intensifies
-> noises, tastes and behavioural patterns are detected by fetus
How heavy is the average neonate?
3.4 kg
When is auditory communication between mother and fetus possible?
28 weeks
Apoptosis
destruction of 25-75% of neurones (unnecessary)
-> surviving neurones reorganised to optimise functioning
Why is apoptosis necessary?
initial over-production ensures that all neurones necessary for life are formed
What are teratogens?
agents that increase the risk of prenatal abnormalities and birth complications
Do teratogens affect all pregnancies in the same way?
no
Sensitive-period principle
effects of teratogen on specific part of a system are more severe while a structure is forming
Which are periods of heightened vulnerability to sensitive-period effects?
Head and CNS: 3-5 weeks
Heart: 3-6 weeks
Other organs and body parts: 5-9 weeks
Which organs are sensitive to teratogens throughout the entire pregnancy?
eyes
genitals
NS
Individual difference principle
susceptibility to harm is influenced by embryo’s/fetus’ genes and mother’s genes
Dosage principle
longer exposure or higher dose are more likely to cause harm to embryo/ fetus
Can multiple teratogens cause the same effect?
yes
Can one teratogen cause more than one effect?
yes
What do long-term effects of teratogens often depend on?
quality of post-natal environment
Sleeper-effect principle
sleeper effect: some effects may not be apparent until later in life
Why are disease teratogens particularly dangerous for embryos and fetuses?
immature immune system
What are the effects of Rubella on the embryo/fetus?
first 8 weeks: high risk of blindness and cardiac abnormalities
6 to 13 weeks: high risk of deafness
3-4 months: high risk of mental retardation
What are the effects of Syphilis on the embryo/fetus?
sypihlic spirochetes can’t cross placenta until 18th week
after: miscarriage or child with eye, ear, bone, heart and brain damage
What does genital herpes cause?
30% mortality rate of infected newborns
blindness and mental retardation
Why are mothers with genital herpes advised to undergo cesarean sections?
babies are often infected when they come in contact with mother’s genitals during birth
What happened during the Thalidomide tragedy?
Thalidomide: mild tranquilizer to treat nausea and vomiting (usually occurs during first 3 months of pregnancy)
taking thalidomide during first 2 months resulted in severe birth defects
-> - 21st day: no ears
-> 25-27th day: deformed or no arms
-> 28-36th day: deformed or no legs
-> after 40th day: baby not usually affected
Why can alcohol consumption affect development?
disrupts function of placenta (even in mild dosages; damage most severe with bingeing)
What are some effects of fetal alcohol syndrome (FAS)?
Microcephaly
deformed heart, limbs, etc.
below average body growth
below average intelligence
When is the sensitive period for the effects of alcohol on development?
there is none
-> damage in early and late pregnancy
Why is cigarette smoking harmful?
disrupts placenta’s ability to provide oxygen and nutrients
nicotine concentration in embryo/fetus’ blood stream 15% higher than mother’s bloodstream
What are some effects of cigarette smoking?
cleft lip
abnormal lung function and hypertension
increased risk of miscarriage and death after birth
below average birth weight and growth
What is the normal weight gain of mothers during pregnancy?
first 3 months: 1-2.3 kg
after: 45 g a week
-> total increase of 11-14 kg during pregnancy
What are the effects of severe malnutrition?
1st trimester: disrupted formation of spinal cord and miscarriage
3rd trimester: underweight newborn with under-sized head
-> death within first year
What effect does adding small doses of magnesium and zinc have?
improves functioning of placenta
reduces incidence of birth complications
What effect does floic acid have and where is it found?
promotes development of neural tube in first 8 weeks of pregnancy
fresh fruit, beans, liver, tuna, green vegetables
What is the safest age for pregnancy?
16-35
Why is birth before 16 dangerous?
lack of prenatal care
socioeconomic conditions
Why is birth after 35 dangerous?
increased risk of miscarriage (increased probability of chromosome abnormalities)
most pregnancies healthy regardless
How does stress relate to prenatal development?
temporary fluctuations: not harmful
chronic and severe stress: decreased heart rate and motor activity
-> reduced prenatal growth, premature delivery and low birth weight
-> irritable temperament, irregular sleeping and feeding habits
Amniocentesis
prenatal screening technique to detect chromosome abnormalities (usually in at-risk women)
large, hollow needle inserted in abdomen to sample amniotic fluid
disadvantages:
cant be performend until 11-14 weeks post-fertilisation due to insufficient amniotic fluid
analysis takes up to 2 weeks
Chorionic Villus Sampling (CVS)
Catheter (thin tube) inserted through vagina and cervix or needle through abdomen
fetal cells extracted from chorion
same tests as amniocentesis, but can be performed during 8th to 9th week and analysed within 24h
Disadvantage: considerably higher risk of miscarriage
-> only recommended for mothers at very high risk
Ultrasound (sonar) imaging
very safe and common
most useful after 14th week
useful to detect gross abnormalities, multiple pregnancies and sex
used to guide other procedures (e.g. amniocentesis)
disadvantage: no invasive analysis (only outline of embryo/fetus)
