EXAM2_HE18_LIMB_Development Flashcards
(36 cards)
What expression at primitive node initiates/maintains primitive streak?
Nodal (TGF-B family)
What expression at primitive streak controls cell migration (invagination)?
FGF8
What expression drives left/right asymmetry later in development?
FGF8 and Nodal expression
Where developed from: Vasculature of limbs? long bones of limbs? Respiratory system? Visceral organs? Gi system? CT?
Vasculature of limbs- Lateral Plate Visceral
long bones- lateral plate Somatic
Respiratory system- lateral plate visceral
Visceral organs & GI- lateral plate visceral
CT- somatic lateral plate mesoderm
MYOTOME differentiation:
2 divisions. What do each form? what expression for each?
When does myotome differentiation occur?
- Hypaxial- body wall & limb muscles- anterior primary rami
(MyoD expression-posterolateral origin of paraxial somite) - Epaxial- Intrinsic back muscles- post primary rami
(Myf5 expression)- posteromedial origin of paraxial somite)
AT 5 WEEKS!
Signaling for hypaxial and epaxial- what about dermis?
BMP4 & WNT>MYOD> body wall/limb muscles
SHH & WNT >MYF5> intrinsic back muscles
NT-3>PAX3>DERMIS
What is special about the epaxial derivatives? hypaxial derivatives?
epaxial ;Myoblasts do not migrate- form intrinsic back muscles
hypaxial- some don’t migrate- form intercostal muscles
some Migrate into the limb muscles
Limb buds- when formed? what type of tissue? where tissue from? location of upper/lower buds? what determined by?
- Buds @ 4 weeks
- Paddles @ 6 weeks
- Fingers @ 8 weeks
-cuboidal ectoderm
-Has dermis deep to ectoderm
-mesenchyme from somatic mesoderm form cartilage>bone
-Upper limb bud C4-T2
-Lower limb bud L1-S2
Determined by HOX genes
mesenchyme>dermis>cuboidal ectoderm layers of limbs
What segments of top part of arm? Lower part of arm?
What segments of lateral leg? midline of leg?
Top surface- c4-c7
Under surface T1-T2
lateral leg- L2-L5
midline leg- s1-s3
Apical Ectodermal Ridge (AER) what causes differentiation? what does it regulate? what kind of cells in differentiation zone? where derived from? when digits formed?
- AER differentiates response from FGF from mesoderm
- Differentiation zone (chondrocytes & CT) Low FGF is proximal
- Proliferative/progress zone Hi FGF-extends limb
- Mesenchyme from lateral plate somatic mesoderm
- cartilaginous digital rays form in each digit 6-8wks
- apoptosis creates digits by 8 weeks
describe the FGF concentration and its role in limb development. High FGF region? low FGF region? what happens there? What it’s called?
Distal End of AER- HIGH FGF= progress zone (proliferative) mitotic
Proximal to AER- LOW FGF = differentiation zone
Nile Blue stain used for?
FGF
What is formed at 8 weeks?
6 and 4 weeks?
8- should have apoptosis and digits of CARTILAGE
6- paddles-Hyaline cartilage
4- buds
Limb development 6 weeks? 8 weeks? 12 weeks? Birth?
what limbs form faster? by how much?
6- limb bones exist as hyaline cartilage models
8- endochondral ossification begins in center of diaphysis
12- primary ossification centers formed
birth- diaphysis is ossified- epiphysis has active secondary ossification centers- branches of intersegmental arteries grow into developing limbs-
Upper limb develop 1-2 days before lower limbs
what is the flow of bone formation?
mesenchyme>cartilage> bv & osteoblasts arrive via blood> ossification
Limb Rotation- When; what rotates how much where?
Begins @ 7 weeks -Upper limb rotates 90deg laterally extensors posterior-thumb lateral flexors anterior thumb lateral
-Lower limb rotates 90deg medially
extensors anterior
flexors posterior
big toe medial
Limb muscle formation and innervation.
- Skeletal myoblasts from HYPAXIAL division of myotome migrate into limb bud by 7 weeks
- CT in the limbs guides myoblast formation of skeletal muscle
problem with CT during limb formation?
if there is a problem with the CT during limb formation the myoblasts will not be patterned correctly
SOMATIC vs SOMITIC
Somatic - referring to lateral plate somatic mesoderm
Somitic- referring to paraxial plate mesoderm somites
What controls the patterns of muscle formation in the limbs? Why is this so important?
Where are occipital/cervical myoblasts derived from?
Where are Body wall/ Limb myoblasts derived from?
CT Fibroblasts (somatic lateral plate)- in buds will direct the myoblasts migration and massing
-Myoblasts migrate within CT in limb buds and develop into specific muscle divisions
Occipital/Cervical muscles- from SOMITIC mesoderm of paraxial mesoderm
Body wall/limbs- SOMATIC mesoderm from lateral plate mesoderm
Where can Connective tissue be derived from?
Head, Cervical/Occipital, Limbs.
Lateral Plate- somatic MAINLY- limb ct for myo formation
Paraxial mesoderm- cervical/occipital ct for myo formation
Neural crest- CT for myo formation of head muscles
Innervation of muscles- What RAMI? 2 divisions of that rami? Functions of each division?
Why is nerve/muscle contact so important?
ANTERIOR PRIMARY RAMI forms appropriate spinal nerves that enter limb buds and has TWO DIVISIONS:
- Anterior division- innervates flexors of limbs
- Posterior division- innervates extensors of limbs
nerve/muscle contact required for complete differentiation
-if muscle develops without innervation- they malfunction
What nerves innervate extensor muscles of the arm and forearm?
Posterior division of the ANTERIOR PRIMARY RAMI forms a posterior nerve:
1. RADIAL NERVE- extensor muscles of the arm and forearm
What nerves innervate Flexor muscles of the arm? flexor muscles of the forearm?
Anterior division of the ANTERIOR PRIMARY RAMI forms 3 anterior nerves:
- MUSCULOCUTANEOUS NERVE- flexor muscles of ARM
- ULNAR & MEDIAN NERVES- flexors of FOREARM
