pre-natal development: elaborate version Flashcards
when is the ‘embryonic phase’
embryonic phase is until 8 weeks post fertilization
when is the ‘foetal phase’
foetal phase is 9 weeks onwards
name the 3 broad tissue types in an embryonic cell mass
- ectoderm (epidermis + nerve tissue)
- mesoderm (skeletal, mm, blood)
- endoderm (GIT, respiratory linings)
how many Carnegie stages or horizons are there in the embryonic period?
23.
fun fact: by stage 23 (week 8) more than 90% of the identifiable structures of the adult body have appeared
what happens in week 1 ?
- cell division with reduction in cytoplasmic volume
- loss of zona pellucida
- free blastocyte
what happens in week 2?
- implantation
- extraembryonic mesoderm
- primitive streak
- gastrulation
what happens in week 3:
- gastrulation
-notochordal process - primitive put
-notochordal canal
-somitogenesis - head fold
somite number 1-3
what happens in week 4
somite 4-12 neural fold fuses
somite number 13-20 rostral neuropore closes
somite number 21-29 caudal neuropore closes
what happens in week 5
somite number 30 leg buds lens placode pharyngeal arches lens pit optic cup lens vesicle nasal pit hand plate
what happens in week 6
nasal pits moved ventrally
auricular hillocks
foot plate
finger rays
what happens in week 7
OSSIFICATION COMMENCES
straightening of the trunk
when does ossification commence?
week 7 yoooooo
what happens in week 8
upper limbs longer and bent at elbow
hands and feet turned inward
eyelids, external ears
rounded body, head and limbs
outline embryonic limb development (and when)
3 weeks: minor swelling appears at site of future limb bud
4 weeks: buds appear at level of lumbar myotomes
4 weeks + 2 days: distends laterally from the trunk
~5 weeks: limb bud extends distal toward sacral myotomes and length increases
tell me some fun facts about embryonic limb development
- all segments lie in transverse plane, relatively perpendicular to the trunk
- all segments are discernible by week 7
- by week 8 there is distinciton between thigh, leg and foot. ossification points of fibula appear. all basic organ development is complete
when do congenital foot deformities occur?
all before the 7th embryonic week… e.g. talipes equinovarus (TEV)
outline embryonic foot development
week 5: foot ‘disk’ recognisable but toes/rays are not yet identifiable.
week 6: inward rotation continues, including of the leg
digital rays become progressively more distinct. toes are spread
@ week 7 the foot structure is clearly recognisable, plantar surfaces face medial, dorsal surface lateral
foot is in equinus. entire limb externally rotated
what happens in week 9-12
- organs cont to grow
- eyelids close
- nails and teeth develop
- genitals appear
- liver is making RBCs
- active (but can’t be felt by mum)
what happens in week 13-16
- skin is transparent
- covered in lanugo (hairy gunk)
- pancreas and liver secretes
- leg is externally rotated at hip, knees flexed, foot in equinus
what is the foot/leg position in week 13-16
leg is externally rotated at hip
knees flexed
foot in equinus
what happens in week 17-28
foetus can hear/swallow
will stretch and move
meconium (dark green first poo)
bone marrow fc
starts to store fat: focus on getting biiig
– leg remains externally rotated at hips, knees flexed, AJs in equinus
what happens in week 29-40
- brain grows rapidly
- some nervous control gained
- lungs still develop
- bones developed
- gains weight
what is the foot/leg position in week 17-28
leg remains externally rotated at hips, knees flexed, AJs in equinus
what’s going on with lower limb/ foot position during the last trimester?
lower limb remains folded in fetal position
feet slightly inverted and PF
one leg/foot is crossed over the other
