Week 4 - Bone Homeostasis Flashcards
What is the process of bone remodeling?
Activation –> Resorption –> Formation/Mineralization
How long does resorption typically take?
~3 weeks for osteoclasts to dig a resorption pit
How long does formation usually take?
3-4 months for osteoid to fill in the pit
How long does remineralization typically take?
years
What is involved in the signalling for cancellous bone formation?
Wnt pathway and hormones
What are the basic steps to remodeling cancellous bone?
- Activation (site of denuded bone)
- Resorption by osteoclasts
- Osteoblasts at site
- Secretion of osteoid
- Mineralization
What is the main difference in how cortical bone is remodeled (compared to cancellous bone)?
Cortical bone is remodeled around a capillary and forms a cutting cone resulting in concentric circles of bone that gets laid down.
What is found at the apex (widest part) of a cutting cone?
Osteoclasts
What is periosteal apposition?
Deposition of bone on the cortical surface
What do osteocytes secrete?
Sclerostin
What is the function of sclerostin?
Antagonist of Wnt & therefore decreases bone formation
What is the most important regulator in bone remodeling?
PTH
What hormones promote bone remodeling positively (ie. anabolic or anti-catabolic) and which ones work on resorption vs formation?
Estrogen - decreases resorption
Calcitonin - decreases resorption
Testosterone - decreases resorption & increase formation
Progesterone - increases formation
PTH (at intermittent dosing) - increases formation
What hormones promote bone remodeling negatively (ie. anti-anabolic or catabolic) and which ones work on resorption vs formation?
Cortisol - suppresses estrogen thus increases resorption; also decreases formation
PTH - increases resorption
