Limb development Flashcards
When does limb development occur?
4-8 weeks
When are limb buds visible?
4 weeks
What are limb buds visible as at end of week 4?
Outpouchings from the ventrolateral body wall
What does the limb bud consist of at first?
Core tissue derived from lateral plate mesoderm
The plate mesoderm is covered in what?
Ectoderm
The mesoderm core differentiates into what?
Mesenchyme which = connective tissue and bones
Skeletal muscle comes from where?
Paraxial mesoderm
What does the paraxial mesoderm differentiate into?
Somites
The somites differentiate into a ventral what?
Sclerotome
Sclerotome forms what
vertebral column
What does the dorsolateral part of the somit form?
Dermomyotome = dermatome and myotome
What does the dermo and myotome give rise to?
Skin and muscle
Myotome differentiates into two parts?
Dorsal epimere, ventral Hypomere
Epimere forms what?
Back muscles dorsal rami
Hypomere forms what?
Thoracic and abdo muscles with ventral
Where does limb muscle come from?
Hypomere region adjacent to upper and lower limb buds
Posterior condensation forms what?
Extensors and supinators
Anterior condensation forms what?
Flexors and pronators
When does limb rotation happen?
6-8 weeks
Upper libs rotate how?
90 degrees laterally
What does the rotation of limbs do that is important to dermotomes?
Spiral around limbs
What does the lateral mesoderm secrete to control growth?
FGF10
What does FGF10 induce?
Thickening of ectoderm apical ectoderm ridge
What does the AER express?
FGF 4 & 8
The rapid proliferation of the mesenchymal cells is called what?
Progress zone
Dorsal ectoderm expresses?
Wnt7
Ventral ectoderm expresses what?
Engrailed - 1
What does engrailed 1 do?
Inhibits Wnt7
Where is craniocaudal axis determined?
Zone of polarising activity
What is expressed at the zone of polarising activity?
Sonic hedgehod
Which direction does Sonic hedgehog move?
Caudally
High concentration of sonic hedgehog does what?
Induces causdal sructures (little finger low concentration = cranial eg thumb
Which week do limb buds flatten?
week 6
What is amelia?
Absence of a limb loss of Fgf
What is Meromelia?
Partial absence of a limb
What is phocomelia?
flipper limb
What is ectrodactyly?
Split hand and foot lobster claw