MSS09 Flashcards
What are the major cell types of bone? What are their functions?
Osteoblast: synthesize the organic components of bone matrix. Produce OPG
Osteocytes: terminal differentiation of osteoblast
Osteoclast: degrade bone marrow matrix protein
what does alizarin/alcian red stain identify?
Calcium stains red. Cartilage stains blue
What drives terminal differentation of osteoclasts?
M-CSF and RANKL (produced by osteoblasts). Osteoblasts also produce osteoprotegerin (which inhibit osteoblast differentiation by binding RANK)
What stimulates osteoclast activity? Inhibits?
PTH and vitamin D. Calcitonin inhibits it.
What histochemical stain can be used to identify osteocytes?
DMP1 (dental matrix protein) and SOST( Sclerostin)
What histochmical stains can be used to identify osteoblasts?
alkaline phosphatase and osteoclacin
Expression of what molecule regulates commitment to the osteoblast lineage?
RunX2 (cbfa-1) and osterix (SP7)
What is the difference between cortical and trabecular bone?
Cortical bone (85% of bone): function is primarily structure. Organized in osteons
Trabecular ( 15%): function is metabolic– high surface area for mineral homeostasis
What is the bone remodeling cycle? Similarities and differences in cortical and trabecular bone?
Trabecular bone is more actively remodeled than cortical bone.
Bone resorption and bone formation are coupled.
Bone resorption is rapid (~2 weeks), bone formation is slow (4-6 mon for full mineralization)
Remodeling of trabecular bone allows buffering of calcium and phosphate content ( mineral homeostasis)
What is the difference beween modeling and remodeling?
Bone growth in radial size and shape change. Mediated by physiological respones to mechanical loading. At level of whole bone: strain is primary stimulus to modeling. At level of cell: shear stress is critical stimulus. Connections among osteocytes allow bone to growth to be directed to sites with greatest strain.
How does a fracture heal?
hematoma forms at fracture size–> Stem cells form soft callus–> blood vessels invade–> bone replaces cartilage ( hard callus)–> remodeling to form lamellar bone and modeling occurs to reduce bulge.
What are the different processes of bone formation?
Intramembranous bone: formed by formation of osteoblasts from mesenchymal stem cells within periosteum. (Bones of skull and ribs)
Endochondral bone: replace cartilage model. Bones grow in length by proliferation of chondrocytes within growth plate. (long bones0
What are the different zones at a growth plate?
- Proliferative zone: chondrocyte division
- Zone of hypertrophy and calcification
- Ossification and resoprtin: blood vessels invade zone of calcified cartilage.
Calcified cartilage is resorbed by chondroclasts and replaced with osteoblasts
What is the primary component of bone ECM?
Type I collagen
How does the structure of bone provide toughness?
Interface between lamellae and between osteons (cement lines) can absorb and dissipate force. Transverse cracks are less about to propagate than longitudinal cracks.
