Prenatal Development Flashcards
Ontogenetic development
The development of an individual over their lifetime
Microgenetic development
Changes that occur over very brief periods of time
Phylogenetic development
Changes over evolutionary time (thousands or millions of year)
Prenatal stage
Conception to birth
Infancy
Birth to 2 years
Preschool
2 - 4 years
Childhood
5 - 12 years
Adolescence
12 - 18 years
Young adulthood
18 - 40 years
Middle adulthood
40 - 65 years
Late adulthood
65 + years
Preformationism
The popular belief (until the 17th century) that miniature people lived in sperm and started to grow when the sperm met the egg
Epigenesis
The term describing what we now know which is that new organs and structures develop through a series of stages throughout prenatal development
Germinal stage
Conception to two weeks
Zygote doubles its cells twice a day
At about 2 weeks, the zygote attaches to the uterus wall and the cells become an embryo
What is a fertilised egg called?
A zygote
Embryo stage
2 - 8 weeks
Period of rapid growth
Key organs and structures develop
Foetus stage
9 weeks - birth
Growth and development of organs
Fewer than ____ of zygotes survive
Half
What is a gene?
A short section of a chromosome
What is a chromosome?
Molecules of DNA that hold the genetic instructions for every cell in our body
How many pairs of chromosomes does a normal human cell have?
23
Which pair of chromosomes determines sex?
23rd
Female sex chromosome
XX
Male sex chromosome
XY
Why are more males conceived than females?
Sperm that carry the Y chromosome are lighter and swim faster than those carrying two X chromosomes
Why are males more vulnerable prenatally?
They are more susceptible to stress and more likely to be miscarried or have birth complications
As they only have one X, if there is a defective gene, they don’t have a functioning copy to balance this out
Monozygotic (identical) twins
The growing cluster of cells breaks apart early resulting in two identical clusters
Dizygotic (non-identical) twins
When two eggs are fertilised at the same time
Where does the zygote attach?
To the uterine wall
What does the inner cell mass become?
The embryo
What does the outer cell mass become?
Amniotic sac and placenta
What is the amniotic sac?
A membrane filled with a clear fluid which provides an even temperature and cushioning
What does the placenta do?
Permits the exchange of materials from the mother to the embryo/foetus via the bloodstream through blood vessels that make up the umbilical cord
Three layers of the inner cell mass, from top to bottom
Ectoderm
Mesoderm
Endoderm
Ectoderm
Becomes the nervous system, nails, teeth, inner ear, lens of the eye, and skin
Mesoderm
Becomes muscles, bone, circulatory system, inner layers of the skin and internal organs
Endoderm
Becomes the digestive system, lungs, urinary tract and glands
What does the neural tube become?
Brain and the spinal cord (central nervous system)
Which areas develop first in the foetal period?
Areas near the head
During the last 5 months, what develops more rapidly?
The lower parts of the body
Foetuses movements
What causes male genitalia to develop?
Presence of androgens (hormones which include testosterone)
What influences prenatal development?
Zygotes genetic code
The environment
What is a teratogen?
Environmental agents (drugs)
Diseases (e.g. measles)
Physical conditions (malnutrition)
Can affect the growing embryo/foetus
What affects the effects of teratogens?
Timings (may only cause damage if exposed at a specific time of development)
Dose-response relationship
What is the dose-response relationship?
The greater the exposure, the more likely the damage
Alcohol on prenatal development
Can lead to foetal alcohol syndrome
Characteristics of foetal alcohol syndrome
Facial defects
Hyperactivity
Behavioural problems
What is the most common teratogen?
Alcohol
