prenatal development Flashcards
Lecture 2/22
what % of organisms that have a spinal cord (chordates) have a bony sheath / skeletal
97%
due to humans having spinal cords which group of organisms does it make us a member of
chordates
how many species of chordates are there
around 6,000 in the world
and in terms of biodiversity amongst other living things there is a actually only a few of us - scientists have named 2 million different species
early scientific views on prenatal development
1590s - invention of microscope
1695 - Nicalaas Hartsoeker and the performation theory of development
19th century - improvements in optics had demonstrated that embryonic development did not involve simple processes of growth but also substantial differentiation.
Nicolass Hartsoeker
1695
the preformation theory of development
the preformation theory of development
nicolaas Hartsoeker - 1695
looked at sperm under a microscope and saw that in the inside of it looked to be a human shaped element
led to the idea if preformation - the idea that development is entirely a matter of growth and the womb acts as place for this expansion to happen within
aristotle - 384-322 b.c.
scala naturae - great chain of being species are fixed and arranged hierarchically
with humans at the top of the scale / ladder of creation
an incorrect idea of evolution
that it is a directional process - a straight line from point a to point b
what is the recapitulation theory
based on aristotle idea of ladder of creation
suggested that the embryo took the form of adult animals further down on the ladder of creation
stages of recapitulation theory
fish phase - suggested due to theorists seeing that human embryos went through a fish like phase
followed by salamander stage of development
etc. tortoise, chick, hog, calf and rabbit before achieving the final goal
stages of prenatal development
- the germinal period - conception to implantation
- the period of the embryo - implantation to 2 months roughly
- the period of the fetus - 2 months to birth
germinal period
sperm cell fertilizes an egg in the fallopian tube
zygote moves down the fallopian tube and into the uterus
4 days after conception the zygote multiplies to form a mass of cells called a mortula
after this the daughter cells decrease and decrease to leave a spherical mass of identical cells called stem cells (can grow into any type of tissue) in this stage the embryo is a blastocyst
finally the embryo implants on the uterus wall
what is a mortula
when the zygote multipies to form a mass of cells
what is a blastocyst
is a stage where the embryo is around 150 cells and has stem cells
happens at around 3 to 5 days
period of the embryo - stage of implantation
happens around 8 weeks post conception
the blastocyst now differentiates into 3 distinct layers of different tissue types as each of these layers develop the become different major organ systems
last 2 months
the 3 types of blastocyst tissue
ectoderm - top layer - nervous system, teeth, finger, nails and outer layer of skin
mesoderm - middle layer - muscles, bones and circulatory system and inner surface of the skin
endoderm - bottom layer - gastrointestinal tracks and major organs e.g. lungs and glands
period of the fetus
this period is concerned with growth as most organs are developed
the liver is already developed and the eyes continue to develop as the brain grows
featus will respond to stimulation at this stage
hearing develops at 20 weeks
4 months there is motor development - movements such as sucking their thumb
by the end of this period featus respond with movement or heart rate changes to temperature changes or touch
when does hearing develop
20 weeks - can detect low frequency sounds of around 250 to 550 hertz
(very narrow hearing band - adults = 20 to 20,000 hertz)
range of a voice
variations from typical development statistic
world health organisation
orgins of congenital aberrations are unknown in 50% of cases
genetics part in variation from typical development
Cystic fibrosis
sickle cell anemia
various chromosomal disorders
environment part in variation from typical development
toxins - thalidomide, alcohol, radiation, pesticides
nutrition - folic acid
how many chromosomes do we inherit from our parents
46 - 23 from each parent
the process of cell dividing in half
mitosis
(supports growth)
mitosis
prophase - duplicate chromosomes in cell
metaphase - chromosomes align at the metaphase plate
anaphase telophase - sister chromatids separate coursing two cells with the same genetic code to exist
Meiosis
happens during the creation of the egg and sperm
so once division has ended you end up with daughter cells that half the original number of chromosomes
human karyotypes
the pictation of chromosomes
chromosomal variations
aneuplodiy - the condition of having fewer or more chromosomes than the usual number coursing developmental issues and learning difficulties
down syndrome - trisomy 21
edwards syndrome - trisomy 18
patau syndrome - trisomy 13
chromosomal variations in the sex chromosome
there are lot of different variations that are compatible with life leading to intersex individuals
a lot more than just xx or xy
define teratogens
are substances that cause birth defects
only effect the fetus affect the implantation phase due to a shared blood supply
the thalidomide tragedy
drug developed in 1954 - to treat headaches, insomnia and morning sickness
by 1961 - the drug had led to 20,000 children in 46 different countries being effected by birth defects such as severely misshapen limbs
only effected children if prescribed during the 1st trimester as the limbs can only be effected during embryo period
fetal alcohol syndrome
course by alcohol effecting the development of the central nervous system
cause unusual facial structure and an under developed brain
children have difficulties with vision and hearing plus face learning difficulties
DeCasper and spence - 1986
fetal learning
N=16 gestation age 7.5 months
read stories 2x a day
tested at 2.5 days after birth
half hear same stories after fast sucking of the dummy and half hear it after slow sucking
result - babies showed preference for familiar stories as they
hepper 1991
neighbors - soap show
sampled mothers who religiously watch the show and those who didn’t
look for difference in their babies when playing the stimulus (show intro) after they were born
found clear difference in the movements of the learning group
