Embryology Flashcards
When does Limb Development Occur?
Weeks 4-8 (mid-late development)
When are limb buds visible?
Week 4
What does limb bud initially consist of?
Lateral Plate Mesoderm covered in Ectoderm
Mesoderm differentiates into bone and connective tissue
Derivation of Skeletal Muscle?
Paraxial Mesoderm > Somites > Dermomyotome >Myotome > Hypomere (Ventral) > Migrates into limb buds
What muscles are formed from anterior condensation?
Flexors and Pronators
Flexors and Adductors in LL
What muscle groups are in the Posterior Condensation?
Extensors and Supinators
Extensors and Abductors in LL
When does Limb Rotation occur?
Weeks 6-8
Which direction does the upper limb rotate?
90 degrees LATERALLY
3 axes of Limb Growth?
Proximodistal (Lengthening of limb)
Dorsoventral (Makes each side different)
Craniocaudal (positions and differentiates digits)
Control of Proximodistal growth?
FgF10 secreted from mesenchyme thickens APICAL ECTODERMAL RIDGE
AER secretes FgF4 and FgF8; stimulates mesenchymal growth in PROGRESS ZONE
Control of Dorsoventral Growth?
Dorsal Ectoderm expresses Wnt7
Ventral Ectoderm expresses Engrailed-1 which inhibits Wn7
Control of Craniocaudal Growth?
Shh produced in ZONE OF POLARISING ACTIVITY on the caudal limb bud
High Shh= Caudal structure e.g. little finger
Low Shh= Cranial structure e.g. thumb
How are the digits differentiated?
Hand and foot plates flatten terminally in Week 6
Apoptosis in AER in Week 8
What is Amelia?
Complete absence
May be due to a loss of Fgf signalling
What is Meromelia?
Partial Limb Absence
Due to later loss of FgF signalling
