Embryology and Teratology Flashcards
teratogenesis
production of congenital birth defects in embryo or fetus
- malformations–> could be internal or external >200 different congenital abnormalites
leading cause of infant mortality in NA, why?
birth defects
- partly due to an improvements in obstetrical care so that other death rates are decreasing
- environmental toxins and drugs
malfunctions
non-reversible morphological defects present at birth
% of birth defects in live births
2-3%
birth defects count for __ of all deaths of children below 1 yr
more than 1/3, after the age of 2 the incident of BD goes up bc we discover BD in organs ( symptoms show later)
- 1/4 of deaths in children under 15 ( this is significant!!)
largest cause of birth defects
unknown causes (65-75%)
what % of BD is caused by known genetic causes
20-25%
other causes of BD
metabolic, infection, drug/chemical, chromosome aberration
less than ___ % of pregnancies result in a healthy, normal infant
50% –> including miscarriages
- majority is post-implantation loss (31%)
largest contributor to the 50% incident of unsuccessful pregnancy
post-implantation loss
- if uterus is not ready to receive the ovum, then the fertilized egg is shred
Each trimester has?
Particular nutritional needs and risk for development
organogenesis happens when? what is it?
- when is the organogenic period? what is it
organogenesis = 3-8 weeks after fertilization, which is the time when division and differentiation of the ovum occurs to form tissue and organs
- organogenic period 17-57 days post fertilization–> critical period with maximal cell division and differentiation ( hyperplasia - 17-8 weeks- time of max vulnerability for teratogenic effects)
teratogenic period
the organogenesis period may also be called the teratogenic period bc it is the most susceptible to birth defects
When does the neural tube close
within 28 days ( most women don’t know pregnant yet)
period of max cell division and differentiation
the organogenic period
- critical period ( organization, differentiating and organogenesis take place)
at the end of the organogenic period
the development the major fetal structures should be complete
hyperplasia
increase in cell number, happen 17 days to 8 weeks after fertilization, max time of vulnerability for teratogenic effects
what occurs day 17- 8 weeks
hyperplasia, could also be the organogenic period
max vulnerability to teratogenic effects
hyperplasia
after 8 weeks
hypertrophy (increase in cell size )
hyperplasia stops after 8 weeks, and now cells get bigger and form into more specialized organs and biochemical structures ( hyperplasia is the base foundation - building out of nothing - like. house- increasing cell size, after 8 weeks this is done and just need to add to the base structure- paint, add drywall –> increase cell size and improve function
higher risk for development of organ or biochemical malfunctions
during hypertrophy stage of development ( after 8 weeks )
pre-implantation –> before 1 week
increase in cell number but not cell size
- exposure to toxins has no effect or only a slight decrease in growth–> due to the fact that the fate of cells is not yet determined (pluropotency)–> they have great restorative capacity and low susceptibility to teratogens
interference with hyperplasia
permenant reduction in cell number which cannot be fixed later ( however before 1 week, exposure to toxins has little to no effect, bc cells are all pluripotent and could just generate, also more protection at this stage - not even in uterus yet
blastogenesis
zygote begins to cleave, increase cell number, producing the morula, then a cavity forms in the center of the morula, the entire structure is now called a blastocysts
blastocysts contain which two cell types
embryoblasts (inside) and trophoblasts (outside)
trophoblast cells secrete proteolytic enzymes which erode the epithelial lining, and allow for fluid and nutrients to be absorbed during the first days before placenta provides food for cells, these trophoblast cells are what well soon form to become the placenta
for the first 20-25 days what provides food for the embryo? what is this phase called? how does food enter?
histiotrophic nutrition phase–> fluid and nutrients absorbed by phagocytosis
histiotrophic phase
the first 20-25 days before the placenta has formed and fluid and nutrients are absorbed by trophoblast cells through phagocytosis to provide nutrients to the blastocyst
where do nutrients come from in the histiotrophic phase
the uterus lining “eating of the uterus”
- this is bc there is no placenta so must rely on the uterus for nutritional support
how does the placenta start forming
the trophoblast forms a cord of cells that extend into the endometrium and attach to start forming the placenta
how is pre-implantation characterized?
increase in cell number but not cell size
- low susceptibility to toxins
why is there low susceptibility to toxins in pre-implantation
cells are pluripotent so the ones that are harmed may just die off and can be rapidly replaced
- and there is less exposure as not in the uterus yet
describe the order from single celled zygote to gastrula
zygote, morula ( about 16-32 cells), blastula (about 100 cells), gastrula( day 14 when the embryobblast cells in the blastula start to differentiate into different cell types
what happens in gastrulation?
- embryo development at around 14 days ( differentiation into 3 layers) During gastrulation (day 2-3 weeks), VERY SUSEPTIBLE TO TERATOGENS 1. primitive streak 2. neurulation: ectoderm differentiates into the neural plate--> neural tube 3. mesoderm and endoderm cells migrate internally to form organs and tissues
the blastula folds in on itself to form three germ layers, the ectoderm, the mesoderm, and the endoderm, that will give rise to the internal structures of the organism. Starts with the formation of the invagination ( Hensons node) and moves gradually forming the primitive streak ( soon to be spinal cord)
definition of a blastula
After the cleavage has produced over 100 cells, the embryo is called a blastula. The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel)
post- ovulation ( 16 days)
following implantation, gastrulation occurs
primitive streak
the faint streak which is the earliest trace of the embryo in the fertilized ovum of a higher vertebrate
- forms the future axis of the fetus and allows the three cells types to form
ectoderm
brain, CNS, skin
mesoderm
voluntary muscles, CVS, excretory organs
endoderm
digestive and Resp, glandular organs
when is VERY susceptible to teratogens
gastrulation, organogenesis
Neurulation
the ectoderm differentiates into the neural plate, forming the neural groove
precursors to CNS
crest cells
edges of the neural groove connect to form
the neural tube
when does gastrulation occur
2-3 weeks
