PRENATAL DEVELOPMENT Flashcards
The 3 main stages of prenatal development and changes that occur during each stage
- Germinal (conception - 2 weeks)
- Embryo (2 - 8 weeks)
- Foetus (9 weeks - birth)
GERMINAL stage of prenatal development
Zygote (fertilised egg) travels down the fallopian tube to the womb.
It then becomes an embryo (2 weeks after fertilisation) as it attaches to the uterus wall.
What is a ZYGOTE?
The fertilised egg formed from the union of egg and sperm and membrane grown around.
EMBRYO stage of prenatal development
A time when the key organs and structures are really rapidly developing.
The embryo grows about 1mm a day!
FOETUS stage of prenatal development
Marks a time in the growth and development of those key organs developed in the embryo stage.
External organs like arms and legs growing quite rapidly too.
Genes
Genes are short segments of chromosomes (molecules of DNA that hole the genetic instructions for every cell in our body).
How does sex determination occur
The 23rd pair of chromosomes determines a person’s sex
Females = XX Males = XY
T/F, it is the Y chromosome that = the development of a male.
SO, gender is determined by the sperm - sperm carrying Y chromosome are smaller/lighter than those carrying the X chromosome, so they can get to the egg faster.
It is the presence or absence of androgens (hormones that include testosterone) that cause male genitalia to develop.
- it is the foetus themselves that produce this hormone, depending on whether they ave a Y chromosome or not.
How do twins arise
When 2 sperms enter the egg @ exactly the same time so the membrane that would normally form to fight off other sperm once one had reached the egg, doesn’t have time to form before 2 sperms are trapped.
MZ twins are identical because they come from the same zygote.
DZ twins - when 2 eggs are fertilised at the same time. They have separate placentas.
What are teratogens?
Environmental influences ie.
- environmental agents (such as drugs)
- diseases (such as German measles)
- physical conditions (such as malnutrition)
Can impair prenatal development, leading to birth defects of prenatal death.
The impact of teratogens on prenatal development
Baby isn’t susceptible to teratogens during the first 2 weeks from conception because placenta has not developed yet.
All depends on which key structures are developing at the TIME.
The greater the exposure, the more likely the damage.
Alcohol = the most common ‘human’ teratogen
- it easily crosses the placenta into the foetuses bloodstream + amniotic sac.
Foetus/embryo won’t have yet developed the structures to metabolise alcohol - this is why it affects them so much - the alcohol stays in their bloodstream for longer.
The impact of alcohol as a specific teratogen
If alcohol is consumed over quite a long period of time or in large/binge doses, this can lead to FOETAL ALCOHOL SYNDROME.
- can lead to quite noticeable facial defects.
- can cause the baby to be quite hyperactive and have behavioural problems.
