Prenatal Development Flashcards
What are chordates?
All animals with spinal cords
What do a majority of these chordates have?
A backbone (vertebral column)
What does biodiversity mean?
The number of different kinds of species in each group of living animals
Describe the species biodiversity
Other insects and beetles are major groups.
No. of chordates are very small
Estimates of how many species on earth = 5-5- million
Describe the similarities of development across species
Diverse species e.g mice + humans = similar gestational processes
all species develop from single eggs, which diversify into complex organisms w/ brains, eyes and mouths.
Who suggested the recapitulation theory?
Suggested by Haeckel when reporting the similarity of forms of early embryos of a variety of species
What is the recapitulation theory?
Popularised in the 19th century. This theory suggests that embryonic development (ontogeny) repeats the evolutionary history of an animal’s ancestors (phylogeny).
Drawing of embryos supported this theory.
How does the recapitulation relate to humans?
Human development occurs in the form of adult animals lower down the evolutionary scale. Animals would stop developing at the appropriate time for their species.
What is a problem with the recapitulation theory?
Technological advancement (photography developing in the late 19th century), shows that this view is not correct.
What can be said learnt from the recapitulation debate?
- Prior beliefs = influence perception
- How reliant science enquiry is on technology
Name 3 examples of improvements in molecular biology that caused an increased understanding of development
1950s - invention of the microscope
1695 - performation theory of development
Late 19th century - improvement in optics
What is Hartoseker’s Performation theory?
Nicolaas Hartoseker saw a tiny human inside a sperm cell when using a more powerful microscope. This popularised the idea that the womb was an oven where tiny humans expanded.
What did the improvement in optics lead to?
Led to embryonic growth now understood to involve substantial differentiation.
What did Aristotle suggested about prenatal development that was popularised around 384-322 B.C?
Suggested a chain of being (Scala naturae) where there was higher and lower life forms - a hierarchy. This idea is widespread outside science.
What are the problems of Aristotle’s suggestions?
Theory suggested evolutionary change is a directional process = false
Misconception that humans are at the top (the most perfect)
What are the three stages of prenatal development?
- The Geminal Period = conception to implantation in the uterine wall
- The Period of the Embryo = implantation to ~2mths
- The Period of the Foetus = 2mths to birth
What is the Geminal Period?
- Sperm and egg cell fuse = zygote (fallopian tube)
- Zygote moves to uterus
- In first 4 days, Zygote cells multiply = mass of cells - morula (daughter cells look the same as parent cells)
- Day 5 = turns into a blastocyst (earliest example of physical differentiation of tissue in the prenatal development )
- Day 8-9 = implantation of blastocyst on the uterine wall making a hypoblast
What is the Period of the Embryo?
- Blastocyst = 3 layers of major tissues (ectoderm, mesoderm and endoderm)
- Post implantation = embryo has identifiable diff. tissues e.g heart, eye, cartilaginous scaffolds but not bones
- One month post-implantation = individual toes, fingers is apparent and gut bulge
What is an ectoderm?
When the blastocyst differentiates into the nervous system, teeth, nails and epidermis (outer layer of skin)
What is a mesoderm?
When the blastocyst differentiates into muscle, bones, the circulatory and reproductive system
What is the endoderm?
When the blastocyst differentiates into the Gastro-intestinal tracts, lungs and glands and systems for excretion and digesting.
What is the Period of the Foetus?
2 mths = limbs well formed, brain expanded and foetus can respond to stimulation
4 mths = touch, movement, hearing (20 weeks at gestational age). Foetal bhvr can be talked about from this age.
8mths = genitalia (can be seen), reacts to temp/ painful stimuli/ light, has preferences in position + will reorient self to it.
What type of hearing do foetus’ have at 20 weeks gestational age?
Low frequency sounds 250-500 Hz
Normal adults is 20,000 Hz
Babies can’t hear much.
What causes a child to vary from typical development?
According to WHO = origins of congenital aberrations are unknown in 50% of cases. They can have genetic or environmental causes.
Genetic example = cystic fibrosis
Environmental experiment = teratogens
Compare mitosis and meiosis
Both produce new cells, use DNA replication.
They are the 2 kind of cell divisions that happen in the body - producing 2 daughter cells that have the same number as the parent cell.
Describe the key points of meiosis
Usually results in gametes containing 23 chromosomes. Each parent gives 23 chromosomes = 46 chromosomes usually
What is aneuploidy?
The condition of having fewer or more than 46 chromosomes, 23 pairs
How many chromosomes do people w/ Down syndrome have?
47 chromosomes, 21 pairs
How many chromosomes do people w/ Edwards syndrome have?
18 pairs = (3 copies of chromosome 18)
How many chromosomes do people w/ Patau syndrome have?
3 copies of chromosome 13
What are chromosomal variations associated with?
Developmental problems in various organ systems + learning difficulties.
True or False?
There is variability in how a chromosome may affect a person.
True - sometimes negative affects don’t always happen
What are the effects of chromosomal variation in sex?
Some, not all = lead to ambiguous genitalia at birth
/ + some cases = ambiguous secondary sex characteristics at birth.
There are more than 2 biological sexes
What is Turner syndrome?
45 chromosomes
1:2,000-5,000
Usually appear female = 95%
What is Klinefelter syndrome?
48 chromosomes
XXXY
1:50,000
Usually appear male until puberty
Learning disability often
What is a teratogen?
substances that can cause physical or functional defects in the embryo/foetus inside the womb
Describe the overall vulnerability of the foetus
At different times of development, diff. developing organs are more/ less vulnerable to teratogens.
Examples
- Central system = vulnerable throughout
- Heart, upper + lower limbs = immune from foetal period
- External genitalia = highly vulnerable in foetal period
- Spine and brain = highly vulnerable in embryonic period
True or False?
The mother and foetus shares the same blood supply before the placenta is formed. This makes them vulnerable to teratogenic influences throughout development.
False - The mother and child doesn’t share the same blood making them immune to teratogenic influence. When the placenta forms and blood supply is shared, this is when the child becomes vulnerable.
Describe the Thalidomide
Thalidomide was developed in 1954 for pregnancy symptoms by the CIBA pharmaceutical company. This only affected children if the drug was prescribed in the first trimester of the pregnancy (misshapen limbs bc highly vulnerable during first trimester).
Describe the Thalidomide Tragedy
- By 1961 = 20,000 children in 46 countries w/ misshapen limbs
- Cause = people didn’t think it was thalidomide bc they didn’t understand chemicals can cross the placental barrier
- Popular idea of cause = widespread testing of atomic bombs pre-1970 in the atmosphere
Why was the US not as affected by the Thalidomide Tragedy?
Thalidomide = never approved by the Food + Drug Administration bc of Dr. Frances Oldham Kelsey
Describe how many cases there were across countries
Cases of thalidomide poisoning
1. US = ~40
2. UK = ~2,000
3. Germany = ~ 2,500
What is foetal alcohol syndrome?
Effects manifests in the developing nervous central = associated w/ neurological problems.
It causes problems w/ vision, hearing and learning. It also causes characteristic facial features and microcephaly.
Describe DeCasper & Spence (1986)
16 Mothers = gestation ages 7.5 mths pregnant read stories 2x a day
When babies = 2.5 days old, played familiar story + new stories in headphones
o Group 1 = sucked faster (high amplitude sucking) = familiar story got louder
o Group 2 = sucked slower = familiar story got louder
Babies = preference for familiar story shows babies were learning during the womb
Describe Harper (1991)
Sampled mothers + babies
o Group 1 (learning) = mothers watched neighbors
o Group 2 (control) = mothers didn’t watch neighbors
Found differences in movement
o G1 = ↑ active when soundtrack was played compared to G2
Describe James’ 2010 review
Fetal learning research is difficult
Habituation = decrease to innate behavioural response with repetition = non-association learning
o Suggested many studies focusing on habituation learning in children = acoustic stimulation but was more like vibro-acoustic bc it is hard to produce pure acoustic stimulus without vibration
Several studies = use exposure to produce data
o H/E = methodological limitation = Not randomised, used ‘sham’ or ‘dummy stimulus e.g James et al. 2002
