skeletal development - Lecture 22/23 Flashcards
What are the mesenchymal origins for different bones of the body?
Mesodermal sclerotomes - vertebral column, ribs and sternum
Lateral plate mesoderm - limb bones and girdles
Head mesoderm - calvaria and base of skull
Neural crest - facial bones
All skeletal tissue derives from mesenchyme, all germ layers are capable of making normal bones
What is the common bone/cartilage differentiation pathway?
Mesenchyme induced into the common pathway
N-cagherins production promotes condensation of mesenchymal cell
TGF-β stimulates fibronectin and N-CAM synthesis
From the common pathway it can go to either membranous bone pathway, permanent cartilage pathway or endochondral bone pathway
Membranous bone pathway
Determined tissue induced by Runs-2 and Osx
These cause the mesenchymal cells to differentiate into osteoblasts
Permanent cartilage pathway
Mesenchymal condesation forms chondroblasts
sox-9 causes chondroblasts to secrete collafen II and cartilage matrix., continually expressed in permantant cartilage
Endochondral bone pathway
Cartilage Induced by Runx-2, ihh and BMP-6 to undergo hypertrophy
Hypertrophic cartilage cells secrete bone proteins and vascular endothelial growth factos
The invading blood vessel erode the cartilege and bring in osteoblasts to replace cartilage with bone
Where do the centrum, neural arches and constal processes of each vertebrae derive from?
Centrum - from ventral and medial parts of paired sclerotomes
Neural arches - dorsal regions of sclerotomes
(Failure of neural arch to form -> spina bifida)
Costal processes - proximal development depends on expression of myotomic myogenic factors, Mft-5 & 6. Distal development is from BMP from somatopleural mesoderm
The occiptal-cervical boundry, cervical-thoracic boundary and the attached-floating rib boundary is marked by anterior expressions of which How genes?
Occiptial-cervicle: Hox 3
Cervical-thoracic boudary: Hox 6
Attached-floating: Hox 9
