Intro to Bone - Blank Flashcards
What is the master transcription factor involved in osteoblast differentiation?
What factors signify that an osteoblast is mature?
Runx2.
High alkaline phosphatase, DMP, SOST (Sclerostin?), DKK1.
What are found in bone canaliculi? What is the major protein involved here?
Canaliculi have cytoplasmic projections between osteocytes which communicate via Connexin-43 gap junctions.
Describe the signaling required for osteoclast maturation.
CSF to stimulate macrophages from bone marrow, then signaling of RANK via RANK-L (opposed by OPG) to promote fusion.
Why is carbonic anhydrase important to osteoclast function?
Bone resorption can only occur under acidic conditions, which is facilitated by the products of carbonic anhydrase (H+, HCO3-).
In a typical long bone, what % of its dry mass is cortical bone?
What is the function served by trabecular bone?
About 80% is cortical.
Metabolic; presumably supports the bone marrow.
How do osteocytes communicate with the bone surface? Why might they do this?
Via cytoplasmic processes & via factors like sclerostin and RANK-L. Osteocytes control bone integrity via osteoblast/clast activation?
What is a Volkmann’s canal?
A canal perpendicular to the length of a long bone, which connects parallel haversian canals.
Distinguish between intramembraneous and endochondral ossification.
Intramembranous ossification occurs in development of flat bones, involves direct mesenchymal-to-bone tranformation, and increases thickness(?)
Endochondral ossificaiton involves conversion of a cartilaginous template to bone, occurs in development of long bones, and increases length.
What is the significance of the epiphyseal growth plate?
In long bones, endochondral ossification occurs at the epiphyseal growth plates, resulting in elongation.
The growth plates seal at particular ages, and so can reveal the “age” of a bone.
Which has a higher rate of turnover: Trabecular or cortical bone?
How are lamellae oriented in each?
Trabecular.
In trabecular, lamellae follow the trabecular curvature. In cortical, they are concentric (osteons).
How much of a bone is typically remodeling at any time?
How long does it take to resorb, then rebuild typical cortical bone?
10%.
2 weeks to resorb, up to 6mo to rebuild.
Describe the structure of a typical bone remodeling unit (BRU).
Osteoclasts at the tip dig through and resorb bone. They are followed by osteoblasts which replace it.
What is the significance of tetracycline in the context of bone mineralization?
Tetracycline appears to disrupt bone mineralization, leaving a distinctive mark (stain?) when given systemically. This can be measured, I guess.
What causes bones to form in a bent shape?
The constantly remodeling bone responds to mechanical stressors; abnormal, prolonged pressure could cause it, but it is more typical of developmental disorders like Rickets.
Briefly summarize the process of fracture healing.
A hematoma forms around the fracture.
A fibrocartilaginous (primary) callus forms, & neovascularization is abundant.
The primary callus is replaced by a bony one.
The bone continues to heal via remodeling for months or years.
