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Bone Resorption
The unique ability of self-renewal in bone tissue
Osteoclasts
• Multinucleated bone cells (many nuclei). • Function: to remove damage or old bone tissue
by creating an acidic environment between bone surface and cell.
• Leaves behind an empty space within bone tissue known as a resorption pit.
Osteoblasts
• Mononucleated bone cells (single nucleus). • Function: to deposit a fresh bone matrix in the
resorption pit left behind by the osteoclasts.• Responsible for the deposition of new bone.
Osteocytes
• Osteoblasts which become stuck in the fresh bone matrix they have recently laid down.
• Communication between osteocytes is vital for bone tissue health.
• Disruptions within this communication network signals for bone to be remodeled or replaced.
Lacuna- Space in which individual osteocytes reside within bone tissue.
Canaliculus- Cellular protrusion which connect individual osteocytes with one another. Forms a communication network within bone tissue.
Osteoclasts
Osteoblasts
Osteocytes
Osteoblast activity must equal osteoclast activity
Summary of Bone Cells
Remodeling
• Why does bone need to be remodeled?– It has become hypermineralized (old) or had been damage.
• How does bone know it needs to under go remodeling?– Disruption in osteocyte communicate initiates the process of
bone remodeling.
Steps of Bone Remodeling
1. Osteoclasts resorb bone. 2. Osteoblasts deposit fresh bone matrix3. Osteoblasts become embedded within this matrix,
transitioning into osteocytes.4. Communication has been re-established.
Blood Vessel
Lining cells
Osteocytes
Osteoblasts
Osteoclasts
Microcrack
Osteocyteapoptosis
Local factors
Cementline
New bone
Animation: Bajaj D. Ph.D., adapted from http://courses.washington.edu/bonephys/physremod.html
Bone Remodeling/Repair
Bone
Osteoporosis
• Osteoporosis is an age related skeletal disease.• Osteoporosis means “porous bone”.• About 10 million Americans are diagnosed
with Osteoporosis, of which 80% are women.
Courtesy of Michael J. Klein, M.D.Fritton & Schaffler, 2008 “Bone Quality”
HealthyOsteoporotic
Pharmaceutical Countermeasures of Osteoporosis
• How can drugs alter this process of bone remodeling?
– Bisphosphonates, which inhibits bone resorption (osteoclast activity).
– Parathyroid Hormone, which stimulates bone formation (osteoblast activity).
Inhibition of Bone Resorption
How do Bisphosphonates Function?
Ruffled Border
Osteoclast Apoptosis
Absence of Ruffled Border
Animation by Bajaj, D. Ph.D.
To think about:
• Why is bone resorption vital to bone health?• What can happen if bone cell activity is not
balanced?• How can drugs treat this imbalance in bone
cell activity which is observed in Osteoporosis?