The cells, which are responsible for removal of bone matrix in bone resorption, are
First, bone remodeling involves two main processes: resorption and formation. Osteoclasts are the cells that break down bone tissue. They do this by secreting acids and enzymes to dissolve the mineral matrix and digest the collagen.
The other cells involved are osteoblasts, which form new bone, and osteocytes, which are mature bone cells. There's also a less common cell type, maybe osteoprogenitor cells, but they're more like precursors.
Wait, the options might include osteoblasts, osteocytes, fibroblasts, or others. Let me make sure. Osteoclasts are derived from monocyte-macrophage lineage, so they're multinucleated. They have a ruffled border that increases surface area for resorption.
Clinical pearl: Osteoporosis treatment targets osteoclast activity, like bisphosphonates inhibiting them. So the key is remembering that osteoclasts are the resorption cells.
Now, I need to structure the explanation with all the required sections. Let me check each part again to ensure accuracy and conciseness.
**Core Concept**
Bone resorption is mediated by **osteoclasts**, multinucleated cells derived from the monocyte-macrophage lineage. These cells secrete hydrogen ions and enzymes (e.g., **cathepsin K**) to dissolve the mineralized matrix and degrade collagen, a process critical for bone remodeling and calcium homeostasis.
**Why the Correct Answer is Right**
Osteoclasts adhere to bone surfaces via integrin receptors and form a **sealing zone** to isolate the resorption site. They polarize their membrane to create a **ruffled border**, enhancing contact with the bone matrix. Acidification (via vacuolar ATPase) demineralizes the inorganic component, while proteases break down collagen, releasing calcium into circulation.
**Why Each Wrong Option is Incorrect**
**Option A:** *Osteoblasts* synthesize and mineralize bone matrix, not resorb it.
**Option B:** *Osteocytes* are mature bone cells that monitor stress and regulate mineral homeostasis but do not resorb bone.
**Option C:** *Fibroblasts* produce extracellular matrix in soft tissues, not bone.
**Clinical Pearl / High-Yield Fact**
Osteoclast activity is inhibited by **bisphosphonates** (e.g., alendronate), a key treatment for osteoporosis. Remember: **"Osteo**clasts = **break** bone; **Osteo**blasts = **build** bone."
**Correct Answer: D. Osteoclasts**