Embryology ii Flashcards
(19 cards)
When do teratogens have their greatest effect?
the earlier the exposure
pre-embryonic = lethal
embryonic = significant effects on system development
fetal- systems already established only CNS vulnerable
What is the sequence of events of early embryonic development?
fertilisation and implantation gastrulation neurulation segmentation embryonic folding
Where is the primitive streak found?
dorsal surface of the embryonic disc
What does it mean if two primitive streaks are identified?
conjoined twins
What happens in gastrulation? What is formed?
migration and invagination
trilamanar disc produced
What are the three layers of the trilamanar disc and what are their fates?
ectoderm- skin/ tissues in contact with outside
mesoderm- supporting tissues
endoderm- internal structures
What causes situs inversus?
immotile cilia
cilia not present to waft signalling molecules to the left affecting L/R signalling cascades in development
What is the notochord?
solid rod of cells in midline of mesoderm layer
How is neural tube created?
notochord release molecules that diffuse a limited distance–>overlying ectoderm thickens and edges elevate out of plane of disc and curl towards each other
What part of the mesoderm is segmented?
paraxial
When does the first pair of somites appear?
day 20 occipital region
What rate do somites appear?
3 pairs/day till 42-44 pairs cranio-caudal sequence
How many somite pairs in total?
31 as some disappear
What does the initial somite look like?
block of mesoderm cells around small cavity
What are the sections of a somite and their fates?
dermatome- dermis
myotome- muscle section
sclerotome- hard tissue section ( bone)
Implications of segmentation?
rise of repeating structures such as ribs, vertebrae and intercostal muscles
What are the two types of embryonic folding? Where does the pressure that causes it come form?
cephalocaudal folding- growth of neural tube–> pressure downwards
lateral folding - somites put lateral pressure on disc
What does the part of the yolk sac pinched of in folding become?
midgut
What membrane surrounds embryo?
amniotic
