Embryology 2 Flashcards
what is the first thing that happens during week 3
a groove/dip forms in the middle of the epiblast region called the primitive streak
what does the formation of the primitive streak signal the start of?
the axis of the embryo
What happens to the cells that start to divide when primitive streak is formed?
these newly formed cells are going to sink down from epiblast and invaginate/ migrate in between the epiblast and hypoblast
what do the cells do once they migrate from the epiblast?
they displace the hypoblast
and form 3 germ layers.
what are the 3 germ layers that are formed from the epiblast
ectoderm
mesoderm
endoderm
what happens when a cell commits to being ecto, meso or endoderm?
cannot reverse this- they are somewhat specialised now- have to progress down that pathway
what does an ectodermal cell form
part of the skin
neural tube
what does a mesodermal cell form
cardiovascular system
muscles
bone
what does an endodermal cell form
certain organs/systems
what happens during gastrulation
formation of the germ layers
how is a notochord formed
cells haven’t stopped dividing at the primitive streak- after forming the 3 germ layers, they continue to divide to form a solid tube (not neurul tube) downwards
they soon lose contact with the ectoderm and form a solid rod of cells called the ‘notochord’
what is a notochord?
a solid rod of cells that sits below the primitive streak in the mesoderm
what happens after the notochord is formed
neurulation (neural tube formation)
what happens after notochord formation
notochord induces ectodermal cells in the midline to form a neural plate that sinks down to forn neural tube that sits between the ectodermal and mesodermal layers
what does the neural tube do to the mesoderm layer first?
it induces it to thicken it
what are the 3 parts called that the mesodermal layer splits into?
paraxial mesoderm
intermediate plate mesoderm
lateral plate mesoderm
what does the paraxial mesoderm separate into?
somites
what does the intermediate plate mesoderm separate into?
urogenital system (kidneys + repro)
what does the lateral plate mesoderm separate into?
body cavity and coverings
what is the 4th-8th weeks period called
embryonic/ organogenetic period
what is the term ‘lateral folds’ describing?
folding of ectodermal layer into a tube - starts in week 3
when are lateral folds are complete
in the 4th-8th week period
what develops from the neural tube
forebrain, midbrain, hindbrain and spinal cord
when does the heart start to beat?
day 24
from which part does the gut form?
the endoderm
how many pairs of somites form in the paraxial mesoderm?
43- these differentiate further
what does a dermatome give rise to
dermis of the skin
what does a myotome give rise to
muscles
what does sclerotome give rise to
bones including vertebrae
somites develop further into which 3 things?
dermatome
myotome
sclerotome
define teratology
Study of when things go wrong during development
what are teratogens
environmental factors that cause abnormal development
what is congenital rubella syndrome caused by
contraction of german measles whilst pregnant
what can malformed limbs be due to
use of thalidomide by mother whilst pregnant
TRUE or FALSE
the majority of caused of abnormal development are of unknown aetiology
TRUE
Environmental causes for abnormal development
drugs- prescription/ recreational/ other
alcohol/tobacco
infectious agents
radiation
examples of infectious agents that can transfer through placenta and affect developing embryo
ToRCH
Toxoplasma, Rubella, Cytomegalovirus, Herpes
genetic factors causing abnormal development
Too many/too few chromosomes
Structural changes - deletions of genes, segments of chromosomes
Turner’s syndrome
45 chromosomes single X
Down’s syndrome
47 chromosomes trisomy 21
what does the risk posed by a teratogen depend on? (3)
exposure during critical periods of development
dosage of drug/chemical/factor
genetic constitution of embryo ie some more susceptible than others at equivalent doses
when is your risk of teratogenesis highest
weeks 3-8
when is your highest risk of death during development
weeks 1-2 but low risk from teratogens
how do you diagnose malformations/ check baby is alright PRENATAL?
Blood - AFP alpha-fetoprotein
Ultrasound scan – 12 week anomaly scan
Invasive tests: chorionic villus sampling and amniocentesis
how do you diagnose malformations/ check baby is alright POSTNATAL? (4)
Hip stability
Testes (descent)
Fingers and toes
Hearing
