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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
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during week 3, as part of gastrulation, 3 primary germ layers develop. Names?
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ectoderm becomes what
- skin
- CNS
- cranial and sensory nerves
- teeth
-
mesoderm develops into what?
- blood vessels
- muscles
- connective tissue
- bone
- urogenital system
- cardiovascular system
-
endoderm becomes
- digestive system
- respiratory system
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nerulation happens at 4 weeks with the formation of __ and __
neural plate and neural tube
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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)
- genetic
- 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
-
syndactyly
- 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?
at diaphysis
-
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)
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