Bone Lecture Flashcards
What is bone considered?
a special CT with a mineralized matrix
What is bone a storage site for?
calcium and phosphate (hydroxyapatite crystals)
What is the major structural component of bone?
Type 1 collagen
How does bone affect blood?
It regulates blood calcium levels (calcitonin and PTH)
Two types of bone structural arrangement?
- compact (outside)
- spongy/trabecular (inside)
Osteoblast
- secretes dentin
- not fully enclosed in matrix
Osteoclast
- eats up dentin
- degrades and remodels bone
Osteocyte
- cell inside of the matrix
Structural components of dried bone
- calcium phosphate (hydroxyapatite crystals) 67%
- collagen 28%
- non-collagenous proteins 5%
General Structure of Bone
- proximal epiphysis: articular cartilage
- metaphysis: spongy bone with red bone marrow
- diaphysis: medullary yellow marrow
- metaphysis
- distal epiphysis:
What surrounds bone?
- periosteum
- endosteum
What are the 2 layers of periosteum?
- outer fibrous
- inner cellular
Where are sharpeys fiber found?
at muscle entheses
What do sharpeys fibers do?
anchor muscle (and periosteum) to bone
What direction are the fibers of perichondrium and periosteum?
Parallel (except at muscle attachments; perpendicular)
Mature bone
- called lamellar bone
- can be compact or spongey
Immature bone
- called woven bone
- has more cells and a diffused arrangement
Ground bone preparation
- loses ALL organic components
Demineralized bone preparation
- loses ALL inorganic components
ID
Volkmann’s Canal
ID
Volkmann’s Canal
ID
Circumferential Lamella
ID
Haversian Canal
Does spongy bone have osteons?
NO
Which type of bone is easier to remodel?
Woven/immature
Woven vs Immature Images
Woven Characteristics
- unorganized lamellar pattern
- more cells per unit area
- more ground substance
Mature Characteristics
- lamellar pattern intact
- less cells compared to woven
- less ground substance; more mineralized
Where are osteoprogenitor cells found?
- cellular layer of periosteum
- endosteum
- canals
Shape of osteoprogenitor cells
- flat and squamous
Role of osteoprogenitor cells
- unspecialized “stem cell” for bone
- produce osteoblasts
- can give rise to any cells in bone
Origin of osteoprogenitor cells
mesenchymal stem cells
Cells of bone labeled
What do osteoprogenitor cells differentiate into?
Osteoblasts
Structure of osteoblasts
- contain increased amounts of ER, GA, and mitochondria
- allows for syntheis and secretion of bone matrix
Function of osteoblasts
- form bone by producing non-mineralized matrix (osteoid)
- regulate osteoclast function
- T1 collagen
- osteonectin and osteocalcin
Location of osteoblasts
- metabolically active at bone surface
What is the most important molecule for bone development?
Alkaline phosphatase
Osteoblastic differentiation?
- Stable beta-catenin plays a major role in inducing cells to form osteoblasts
What induces osteoblast differentiation?
- PDGF
- IDGF
Osteoclast activation
- Via PTH receptors on osteoblast
Osteoclast inhibition
- Osteoblasts can secrete OPG (osteoprotegrin)
- OPG binds to RANKL and inhibits osteoclast activity
What stimulates bone production?
Estrogen
What inhibits bone (matrix) production?
Glucocorticoids
What stimulates bone resorption?
Prostaglandins
What inhibits bone resorption?
Estrogen
Osteoblast EM
Osteoblast EM
Bone attributes image
Osteocyte origin
Former osteoblasts trapped in matrix form 90% of cells in the mature skeleton
Osteocyte structure
- High nucleus to cytoplasm ratio
- Have long cellular processes for communication via canaliculi in the bone
Osteocyte function
- CANT DIVIDE (bc theyre enclosed in bone)
- maintain bone and cellular matrix
- important in regulation of calcium and phosphorus in bone
Osteocyte signaling
- Stimulated by calcitonin
- Inhibited by PTH
- Communication with osteocytes via gap junctions in canaliculi
What anchors osteocytes to canaliculi walls?
tethering fibers
What are bone lining cells?
Spindle-shaped cells on the surface of bone
Where are bone lining cells located?
Endosteum and periosteum
Bone lining cell origin
Mesenchymal stem cells
What can bone lining cell yield
- High oxygen and Low strain = osteoblasts
- Low oxygen and Intermediate strain = cartilage
- High strain = fibrous tissue
Bone lining cell image
Osteoclast function
reabsorb bone
Osteoclast origin
myeloid hematopoietic cells from monocyte/macrophage cell lineage
Osteoclast image
Osteoclast image
What is bone resorption
bone matrix breakdown
Bone resorption image
Bone resorption image