Flashcards in Lect. 22 - Skeletal System Devpt. I Deck (16):
What parts of the skeleton originate in the lateral plate mesoderm?
Limb bones and girdles
What parts of the skeleton originate in the head mesoderm?
Calvaria and base of skull
What parts of the skeleton originate in the neural crest?
Describe the common pathways of the bone/cartilage differentiation pathways
Mesenchyme is induced to enter the common pathway; production of N-cadherins which promote mesenchymal cell condensation; TGF-beta stimulates synthesis of fibronectin and N-CAM; aggregated state of mesenchymal cells is stabilized.
Describe the membranous bone pathway of the bone/cartilage differentiation pathways.
Requires TFs Runx-2 and Osx; mesenchymal cells differentiate into osteoblasts
Describe the permanent cartilage pathway of the bone/cartilage differentiation pathways.
Mesenchymal condensation forms chondroblasts; Sox-9 causes chondroblasts to secrete collagen II and cartilage matrix; Sox-9 is continually expressed in permanent cartilage.
Describe the endochondral bone pathway of the bone/cartilage differentiation pathways.
Runx-2, ihh, and BMP-6 induce this cartilage to undergo hypertrophy; hypertrophic cartilage cells secrete bone proteins and vascular endothelial growth factor; invading blood vessels erode the hypertrophic cartilage and bring in osteoblasts to replace cartilage w/ bone
Origin of the centrum
Derived from ventral and medial parts of paired scleretomes
Origin of neural arches
Arise from dorsal regions of sclerotomes
Origin of costal processes/ribs
Proximal development depends on expression of myotonic myogenic factors, Myf-5 and Myf-6; distal development depends on BMP signals from somatopleural mesoderm
Attached-floating ribs boundary
What is the origin of the sternum?
Derived from lateral plate mesoderm; arises as a pair of cartilaginous bands that fuse then subdivides into craniocaudal elements
What is the origin of the clavicle?
Arises from neural crest; follow intramembranous pathway; one of the first bones to become ossified