MSCT Week 4: Musculoskeletal Embryology Flashcards
When does embryo folding occur?
occurs between 18-24 days after fertilization
What is embryo folding?
the Trilaminar embryo undergoes cranial - caudal and lateral folding to form the tube within a tube body plan
Identify process
As a result of embryonic folding the top of the yolk sac becomes?
what about the mesoderm surrounding this new structure?
the gut tube which is suspended within the tube of the body by mesoderm surrounding it which becomes the wall of the gut (connective tissue, smooth muscle, blood vessels)
As a result of embryonic folding, the endoderm becomes?
Epithelial lining of the gut
As a result of embryonic folding, the ectoderm becomes?
epithelium of the skin
As a result of embryonic folding, the mesoderm becomes?
becomes the components of the body wall and limbs (bone, connective tissue, smooth muscle, blood vessels)
Identify
Lateral Plate Mesoderm is subdivided into?
- Somatic Mesoderm
- Splanchnic Mesoderm
Somatic mesoderm is in contact with?
The ectoderm
Splanchnic mesoderm is in contact with?
endoderm
After folding of the embryo, splanchnic mesoderm…
surrounds the gut tube and forms the wall of the gut
Splancha means?
Viscera or guts
Splancha Mesoderm AKA
Visceral Mesoderm
After embryoinic folding, the somatic mesoderm…
forms components of the body wall and limbs
Somatic mesoderm forms
3 listed
- connective tissue and smooth muscle in the body wall and limbs
- components of the body wall and limbs
- appendicular skeleton (bones of the limbs)
Paraxial mesoderm forms
2 listed
- the axial skeleton (vetebral column and ribs)
- skeletal muscle in the body wall and limbs
Limbs develop from
lateral plate mesoderm
When do Limbs develop?
4-8 weeks
How do limbs start developing?
Initiated by embryonic induction
Intermediate mesoderm produces FGF8
FGF8 induces the overlying ectoderm to form the apical ectodermal ridge
The AER is thickened ectoderm that maintains the proliferation of underlying somatic mesoderm cells (the progress zone) through production of FGF4 and FGF8; it promotes outgrowth of the limb bud along the proximal/distal axis (shoulder to fingers)
How limbs begin to develop
- Intermediate mesoderm produces FGF8
- FGF8 induces the overlying ectoderm to form the apical ectodermal ridge
- The AER is thickened ectoderm that maintains the proliferation of underlying somatic mesoderm cells (the progress zone) through production of FGF4 and FGF8; it promotes outgrowth of the limb bud along the proximal/distal axis (shoulder to fingers)
Limb development diagram
Progress zone
Process of embryonic induction of limbs
Lateral plate mesoderm is induced between weeks 4-8
intermediate mesoderm produces FGF8
FGF8 induces the lateral plate mesoderm to produce FGF10
FGF10 induces the overlying ectoderm to form the Apical Epidermal Ridge (AER)
The AER is thickened ectoderm that maintains the proliferation of underlying somatic mesoderm cells (the progress zone) through the production of FGF4 and FGF8; it promotes outgrowth of the limb bud along the proximal/distal axis (shoulder to fingers)
Experimental removal of the AER results in? & interpretation
Truncation of the limb (meromelia or amelia)
this confirmed a role for the AER in regulating the development of the proximal/distal axis of the limb
it demonstrated that the cells of the limb bud differentiate in a proximal to distal pattern
Selective loss of the AER facilitates the formation of?
the digits by reducing the amount of FGF in the region of the interdigital spaces, leading to cell death (apoptosis) and cessation of cell proliferation in these areas
Selective loss of AER causes?
Zone of Polaraizing Activity description
is a specialized mass of cells in the base of the limb bud that regulates development along the cranial (anterior)/caudal (posterior) axis