MSK Flashcards
What kind of tissue includes bone and cartilage?
Connective / mesenchymal tissue
Why is the non-living intercellular matrix secreted by living bone/cartilage cells relevant to injury/healing?
Tissue is avascular in nature, meaning that it is slow to heal
What are 2 kinds of mature bone tissue?
- Compact bone
- Cancellous (spongy) bone
What is the membrane that covers bone?
Periosteum
Why is the vascular nature of periosteum relevant to bone injury?
Fractures result in bleeding
Endosteum is a membrane that lines which 3 structures?
- Spaces of spongy bone
- Marrow cavities
- Haversian canals of compact bone
What is the term for the heads of long bones?
Epiphyses
What is the term for the shaft of long bones?
Diaphysis
What is the term for the widening part of the bone between the shaft and the epiphyseal plate?
Metaphysis
In children, a fracture can affect growth/development if which structure is involved?
Epiphyseal plate
Why may myeloid cancers affect bone homeostasis?
Osteoblasts and osteoclasts originate in bone marrow
What is the unit of bone tissue?
Osteon
What is the term for the “rings” seen in bone tissue?
Concentric lamellae
What is the term for the space in the centre of an osteon where a blood vessel runs through?
Haversian canal
What is the length of time of the adult cycle of bone remodelling?
4 months
What is the name for the undifferentiated stem cells of osseous tissue?
Osteoprogenitor cells
What is the name for bone building cells that synthesize and secrete organic (protein) matrix of bone?
Osteoblasts
What is the name of mature bone cells that maintain bone matrix and release calcium into blood?
Osteocytes
What is the name for bone cells that resorb bone matrix and release calcium & phosphate from bone?
Osteoclasts
How do osteoclasts work to resorb bone?
Remove both protein and mineral components creating a tunnel-like space in the osteon
What is the approximate composition of new bone?
60% mineral
20-25% organic (collagen)
20% water
What cell lineage are osteoclasts derived from?
Monocyte/macrophage precursors
What are 3 functions of osteoblasts?
- Deposition of organic matrix (osteoid) on wall of canal created by osteoclasts
- Deposition of bone lamellae
- Release RANK-L to induce osteoclast activity
What produces RANK ligand, and what is its function?
Produced by osteoblasts
Binds to RANK receptor on osteoclasts, causing osteoclast differentiation and proliferation
What produces osteoprotegerin (OPG), and what is its function?
Produced by osteoblasts
Destroys RANK receptors and acts as an antagonist for RANK-L
How are bisphosphonates released, and what is their function?
Released during bone resorption, concentrated under osteoclasts
Inhibit osteoclast activity, promote osteoclast apoptosis, modulate signaling from osteoblasts to osteoclasts
What 3 hormones promote osteoblast secretion of OPG to inhibit osteoclasts?
- Growth hormone
- Thyroid hormone
- Sex hormones
What are 3 functions of vitamin D and parathyroid hormone?
Stimulate osteoblasts to:
1. Produce RANK-L and IL-6 (activate osteoclasts)
- Produce M-CSF (increase osteoclast differentiation
- Decrease secretion of OPG
What are 4 functions of calcitonin, and in what population does it have a major role in?
- Binds directly to osteoclast receptors to inhibit their activity
- Increases renal elimination of Ca and PO4
Plays a major role in children’s growth/development
What are 3 functions of parathyroid hormone, and in what population does it have a major role?
- Increases release of Ca and PO4 from bone
- Increases conservation of Ca and elimination of PO4 by kidney
- Increases intestinal reabsorption of Ca via vitamin D (calcitriol)
Plays a major role in adults
What are 2 functions of activated vitamin D (cholecalciferol)?
- Increases absorption of Ca from intestine
- Inhibits actions of PTH
What are the different forms that vitamin D is converted into?
Vitamin D > cholecalciferol (hormone) > calcidol (inactive) > calcitriol (very active)
What may paradoxically happen if a person with hypocalcemia takes exogenous vitamin D?
It would cause bone resorption as vitamin D only regulates blood calcium. Blood calcium must be sufficient for vitamin D to promote bone mineralization
What are 3 clinically relevant ways that causes osteoclast upregulation and activation?
- Inflammation
- Immune activation
- Corticosteroid treatment
What microscopic features of osseous tissue help long bones withstand lateral stress without fracturing?
Concentric lamellae (as in a tree)
