embryo-limb development Flashcards
two layers of a developing embryo
embryoblast
trophoblast
embryoblast forms
epiblast
hypoblast
trophoblast forms
syncytiotrophoblast
cytotrophoblast
what happens on day 16 of development?
gastrulation occurs
from bilaminar to trilaminar
three layers that result from gastrulation
endoderm
mesoderm (layer that forms due to gastrulation)
ectoderm
what occurs during neurulation
formation of neural tube
mesoderm forms paraxial, intermediate and lateral plate on either side of neural tube
paraxial mesoderm organizes into what
somitomeres that become somites
how many somites by day 35
42-44 somites
somitomeres in the head form
neuromeres not somites
somites from from which somitomeres
occipital region to caudal region
what are the regions of somites
4 occipital 8 cervical 12 thoracic 5 lumbar 5 sacral 8-10 coccygeal
1st occipital and last 7 coccygeal disappear
what two layers do somites differentiate into
sclerotome
dermomyotome
what does the sclerotome give rise to
vertebrae and most of skull axial skeleton rib cartilage bones of the trunk
what do bones first appear as
condensations of mesenchyme cells
what are the two methods of bone development
intramembranous
endochondral
intramembranous
mesenchyme cells are just replaced by bone cells or osteocytes
endochondral
mesenchyme become chondrocytes then form bone cells or osteocytes
lateral plate mesoderm forms
sternum and limb bones
neural crest forms
bones of the skull
head somitomers form
forms the cranial vault and base of skull
what two layers does the dermomyotome give rise to
dermatome
myotome
dermatome gives rise to
dermis and subcutaneous tissue
myotome gives rise to
muscle
myoblasts fuse to form myotubes which fuse to form muscle fibers
abaxial muscle cell precursors form what
ventrolateral muscle cells
limb muscles
abdominal muscles
infrahyoid muscles
pimaxial muscle cell precursors from what
dorsomedial muscle cells
muscles of the back
shoulder girdle
intercostal muscles
muscle cells from the limbs are derived from
somites from specific segmental levels
epaxial
intrinsic back muscles
from primaxial
hypaxial
body wall and limb muscles
from abaxial
how do vertebral column forms from sclerotomes
caudal portion of each sclerotome proliferates and fuses with cranial portion of inferior sclerotome
intersegmental
notochord forms
nucleus pulposus
mesenchyme forms
annulus fibrosus
congenital scholiosis
asymmetric fusion of vertebra
appears that half of the vertebra is missing
abnormal curvature of the vertebral column
accessory ribs due to
extra vertebral body
fused ribs due to
missing a vertebral body
klippel-feil anomaly (brevicollis)
short neck because of the absence or fusion of cervical vertebra
at craniovertebral junction
1% of new borns
how do limb buds appear
as outpocketings from ventrolateral body wall
limb buds consist of
core of mesenchyme surrounded by surface ectoderm
upper limb buds appear by day
day 26
lower limb buds appear by day
day 28
mesenchyme is
somatic layer of lateral plate mesoderm
mesenchyme contributes to
bones tendons ligaments cartilage fascia joints vessels dermis
homeobox (hox) gene does
regulates axes and patterning
AER is essential for
the proximal-distal axis of limbs
AER stands for
apical ectodermal ridge
what forms AER
apex of each limb bud thickens to form, mutilayered
AER induces
proliferation of underlying mesenchyme
AER causes which mesenchyme to remain undifferentiated
adjacent mesenchyme
ZPA is responsible for
patterning of the anterior-posterior axis of limbs
how does ZPA form
mesenchymal cells aggregate at the posterior margin of the limb bud forming a zone of polarized activity
retinoic acid
should not be taken during pregnancy. can cause duplication of limbs
normally cells in ZPA release it already
hand and foot pads form
distal ends of the limb buds flatten
what does mesenchyme do in hands and feet
mesenchyme condenses to form digital rays by 6th week for hands and 7th weeks for feet
what causes formation of separate digits
apoptosis between digits
each finger still has AER to continue distal growth
when does mesenchyme form cartilaginous models of the limb
6th week
mesenchyme to chondrocytes to cartilage
when doe endochondral ossification begin to form limb bones from lateral plate mesoderm
8th week
by what week have all bones form
12th week
when does secondary ossification center form
at birth
how do limbs rotate to each anatomical position
upper limbs rotate laterally through 90
lower limbs rotate medially almost 90
how does dermatome start
segmentally then changes
initial blood supply to upper limb
dorsal intersegmental arteries from aorta
primordial vascular pattern consists of
primary axial arteries
what does the axial artery become
brachial and then common interosseous
what are the secondary branches from the brachial
radial and ulnar arteries
which artery degenerates
median artery
what does the axial artery begin as
ischiadic atery
primary axial artery is represented by
profunda femoris
popliteal
posterior tibial
minor limb anomalies are how common
fairly common
what is critical period for limb anomalies
4th-5th weeks
how often do major limb anomalies occure
1/500
usually genetics
major cause of limb defects from 1957-1961
thalidomide
bone malformations
failure to develop
formation of extra bones
fusion of adjacent digits
achondroplasia
cause of dwarfism
1/15000
bowed limbs and short
disturbance of endchondral ossification at epiphyseal plates
thanatophoric dysplasia
lethal skeletal dysplasia
1/20,000
respiratory failure
fibroblast growth factor receptor deficiency
osteogenesis imperfecta
deficient in type 1 collagen
early hearing loss, protrusion of eyes, bowing of legs, fractures. blue-gray sclera.
amelia
absence of entire limb
meromelia
absence of part of limb
cleft hand or foot (extrodactyly)
lobster claw deformity
absence of central digit
failure of digital rays to form
brachydactyly
shortness of digits
associated with short stature
polydactyly
supernumery digits
extra digits usually useless
extra digits is medial or lateral
toes not in center, useless
syndactyly-two types
1/2200
webbed digits
cutaneous (webbing of digits)
osseous (fusion of bone)
congenital clubfoot
generally any defect with talus
1/1000
abnormal orientation of the foot that prevents normal weight bearing
inconclusive evidence for restriction movement in utero as cause
environmental factors
congenital dislocation of hip
1/1500
results from laxity of the joint capsule or underdevelopment of the acetabulum
