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when is the pre-embryonic phase
- first 3 weeks
- placenta formation
when is the embryonic stage? what happens here?
- weeks 3-8
- organogenesis (organs develop)
- bc new structures are developing rapidly, this is a very vulnerable time for the embryo, and this is unfortunate, since at this stage lots of ladies don't even realize they're pregnant
when's the fetal period
what happens here?
- 8-40 weeks
- maturation and growth of all structures & organs
during week 3, as part of gastrulation, 3 primary germ layers develop. Names?
ectoderm becomes what
- cranial and sensory nerves
mesoderm develops into what?
- blood vessels
- connective tissue
- urogenital system
- cardiovascular system
- digestive system
- respiratory system
nerulation happens at 4 weeks with the formation of __ and __
neural plate and neural tube
what induces what to thicken and form the neural plate
notochord ... ectoderm
neural plate gives rise to __
neural plate invaginates to form ___
- CNS (via the neural tube, which comes when the neural plate invaginates to form neural folks, and the folds fuse to form the tube)
- neural folds
where does the neural tube come from
notochord induces ectoderm to thicken to form the neural plate which invaginates to form neural folds which fuse to form the neural tube
failure of neural tube to close at top --> ?
at bottom -->
- cranially: anencephaly = no brain
- caudally: spinal bifida at thoracic or lumbar region
neural tube runs from __ to __
forms the __
closes at top and bottom by __
- hindbrain to S2
- CNS (brain & spinal cord)
- day 28
neural plate forms the __
- neural crest, which forms the PNS
- (so, ectoderm forms neural plate which gives rise to neural tube, and crest of the NP becomes the PNS, and the NT becomes the CNS)
3 reasons neural tube might not close (NTD = neural tube deficits)
- nutritional (take your folic acid supplements!)
- environment (exposure to toxins... bad)
apical ectodermal ridge (AER) -- what, when, secretes what?
- the apex of each limb bud (UE limb buds appear at 4th week, LE limb buds appear 2 days later)
- AER secretes fibroblast growth factor inducing limb growth
6 weeks cool detail about how fingers and toes form
- at this points we just have paddles
- then there's programmed cell death, leaving distinct digits
- webbed fingers (due to programmed cell death not happening right)
- most common limb anomaly
creating skeleton in the limbs...
- as limb lengthens menenchymal bone models undergo chondrification to form hyaline cartilage bone
- end of week 7, entire limb is cartilaginous, and there's an embyonic skeleton
ossification begins where?
what's the process by which cartilage is replaced with bone?
- endochondral ossification, w cell death occuring to leave holes for blood vessels to grow in
- osteoblasts invade and osteogenesis occurs
disturbance of limb buds at 4th week, at 5th week, at 8th causes...
- 4th: absent limb
- 5th: partial limb formed
- 8th: teratogens can't cause major limb deficiencies
FGFR3 disturbs what process, causing what?
- converting cartilage into bone, esp in long bones
- 70% of Dwarfism
- this is an autosomal dominant issue, limiting osteogenesis / endochondral ossification
- the condition is called achondroplasia
achondroplasion clinical manifestations
- cuboid shaped vertebra --> narrowing of spinal canal --> compression
- --> spinal stenosis, lordosis, kyphosis
- also tibia vara (bow-legged)
what do do with a kid with achondroplasia presenting w hypotonia and transient kyphosis
- discourage early unsupported sitting
- consider bracing
- (10-15% kyphosis is fixed)