Bone Flashcards
What is bone composed of?
Similar to dentin (but not anatomically)
HA overlaid on a collagen I scaffold
-67% - Inorgo - HA
-33% - Orgo
—28% - Collagen
—5% - Noncollagenous proteins
What are the non-collagenous proteins in bone?
Bone sialoprotein (BSP)
Osteopontin (OP)
Osteocalcin (OC)
Osteonectin (ON)
Matrix extracellular phophoglycoprotein
What 3 cell types are in bone?
Osteoclasts
Osteoblasts
Osteocytes
What are 4 physiological roles of bone?
Structural
Ca2+ homeostasis
Reservoir for growth factors in tissue repair
Hematopoietic and mesenchymal progenitor cell populations in marrow
Calcitonin does what?
Removes Ca2+ from blood and put it into bone
PTH does what?
Takes Ca2+ from bone and puts it into blood
What is the macrostructure of bone?
Outer layer of dense, compact (cortical) bone, with an inner cavity
Inner cavity with marrow, red or yellow, and cancellous trabecular bone
HIGHLY VASCULAR
T/F - Cholera diarrhea disturbs Ca2+, drops significantly, and is pretty much plasma diarrhea.
TRUE
What are the 3 organizational units of compact bone?
Circumferential - Outer ring of bone tissue
Concentric (osteonic) lamellae - Intact osteons
Interstitial lamellae - Fill space b/t concentric lamellae, former concentric lamellae
What is the basic functional unit of compact bone?
The osteoblasts
Look at slide 6. Picture of bone with labels
Do it
An osteon is formed from?
Concentric lamellae
Basically concentric rings of bone, built around a canal housing a capillary (Haversian Canals)
What links Haversian canals?
Volkmann canals
What heals faster, bone or cartilage?
Bone
-It is much, much more vascular than cartilage
Where there is blood, there is healing
Where is cancellous bone found?
Spongy bone
End of long bones, in apposition to jts and is associated w/ the marrow spaces
What does cancellous bone do?
Provides structure support for marrow tissues, highly vascular
Site of blood cell production, supports mesenchymal and hematopoietic progenitor cell populations
Layers of bone from outside in.
Periosteum
Outer Circumferential lamellae
Osteonic lamellae
Haversian canals
Inner circumferential lamellae
Endosteum
Marrow cavity with trabecular bone
How is the periosteum connected to the outer surface of bone?
SHARPEY’S FIBERS
Outer fibrous layer and inner layer in apposition to the bone surface
Which layer of the periosteum is highly cellular and vascularized, outer or inner?
Inner layer
What is endosteum?
Loose connective tissue covering the inner surface of both cancellous and compact bone
Separates the marrow from the bone
T/F - Volkmann’s canals connect osteons, while osteons are built around Haversian canals.
TRUE
What are osteoblasts?
Bone forming cells with MESENCHYMAL origin
What are osteocytes?
Bone cells
- Encapsulated osteoblasts
- Housed in osseous lacunae
What are osteoclasts?
Cells which break down bone tissue. HEMATOPOIETIC origin
Osteoblasts, clasts, and cytes are responsible for what?
Bone formation, repair, and maintenance
Tell me more about osteoblasts.
Mononucleated cells that synthesize osteoid matrix
MESENCHYMAL origin (Ectomesenchymal in the head)
Differentiate in response to a cascade of growth factors
Bone formation and repair
Communicate with each other via gap junctions, do NOT form complexes
T/F - Osteoblasts produce osteoid matrix similar to odontoblasts.
TRUE
Osteoblasts secrete what?
Collagen
Non-collagenous proteins via vesicles
Growth factors
TGFbeta1, BMP2, IGF I and II, PDGF, FGF)
Once bone is formed, they flatten and from bone lining cells
What are osteocytes?
Osteoblasts which have been embedded into the bone matrix
They are the endgame of healthy osteoblasts
What do osteocytes occupy?
Lacunae in bone tissue
Interact with each other
What are osteoclasts?
Fusion of monocytes
HEMATOPOIETIC ORIGIN
What do osteoclasts do?
Resorption of bone
Activated in inflammation
-IL-1beta, TNFalpha
Key marker
—Tartrate Resistant Acid Phosphatase (TRAP)
How are osteoclasts attached to surface?
Integrin, cytoplasm adjacent to surface rich in talin, actin, and vinculin
Form a ruffled border in apposition to bone
Form resorption pits (Howship’s lacunae)
-Secrete H+ ions and matrix degrading enzymes
What is osteoid?
Bone protein, unmineralized
What is the zone b/t Howship’s lacunae and intact bone?
Lamina limitans
Osteoblasts/osteoclasts are supplied by what?
Progenitor cell populations
Differentiate in response to signaling cascades
Also triggered by tissue damage, inflammation, repair signals
What is bone formation controlled by?
Complex interactions b/t osteoblasts and osteoclasts
Balance b/t synthetic and resorptive signals
Osteoblasts regulate osteoclast fx RANK-RANKL-OPG system
What is RANKL?
Receptor Activated Nuclear Factor kappaB Ligand
OSTEOBLASTS
What is RANK?
Receptor Activated Nuclear Factor kappaB
OSTEOCLASTS
What is OPG?
Osteoprotegerin
Produced by osteoblasts binds RANKL
Bone development types.
Endochondral bone formation
-Long bones
Intramembranous ossification
-Bones of the skull
Sutural bone growth
-Fusion of skull plates
*These are not necessarily exclusive processes
What is the most important factor in ossification?
Vascular supply
Tell me about endochondral formation.
Bone formed on a hyaline cartilage pattern
Condensation of mesenchymal cells into chondrocytes
Collagen is secreted, mineralizes, and is broken down by chondroclasts
—This allows for penetration of vasculature
With vasculature comes from ________ cells which differentiate into osteoblasts.
Mesenchymal
What makes up the primary spongiosa?
Bone matrix surrounds remaining mineralized collagen which forms mixed spicules
__________ gradually remove mineralized cartilage and develop marrow cavity.
Osteoclasts
Secondary growth centers from what?
Epiphyses of long bones
-Growth plates
Tell me how PTH leads to resorption. THIS IS IMPORTANT
PTH activates osteoblasts
Osteoblasts express higher levels of RANKL
RANK on Osteoclast binds to RANKL
This leads to resorption
Tell me about PTH and quiescence. THIS IS IMPORTANT
PTH activates osteoblasts
RANKL is blocked by OPG (OPG is produced by osteoblasts)
OPG binds RANKL and competes with RANK
This is a negative feedback loop
This leads to quiescence
SLIDE 18
Tell me about intramembranous formation.
Mesenchymal cells condense in fibrous CT, differentiating into osteoblasts and forming an ossification center
Osteoid is secreted into the CT matrix and is penetrated by bvs
-Rapid formation of mineralized woven bone
Woven bone is remodeled into mature trabecular bone w/ a collar of cortical bone around it
Tell me about sutural bone growth.
Fusion of skull plates
Sutures are fibrous CT bands b/t plates
-Allows for internal expansion of organs
Inner Cambrian layer associated with periosteum
Outer capsular layers meet to join sutures together
Gives the skull some “flex”
Children bone turnover ___-_____% of their bone per year.
30-100%
Also addition to bone
T/F - Adult bone turnover - 5% cortical and 15% trabecular per year.
TRUE
Mostly just remodeling
Most bone is formed around the _______, while it is mainly resorbed form the _______.
Periosteum
Endosteum
What oversees bone remodeling and repair?
Cascade of factors
-Growth factors
What happens in remodeling of cortical bone?
Primary osteons replaced by secondary osteons, which are replaced by tertiary osteons
Allows for bone growth
__________ resorb bone, leaving a space which is filled by trailing ___________.
Osteoclasts
Osteoblasts
Osteoblasts create a _________ line (of what?) and lay new bone onto it.
Cement
Non-collagenous proteins
T/F - Osteons must be first broken down to put a new osteon in that spot.
TRUE
There is also a cutting cone v filling cone where the leading edge is the osteoclasts and trailed by osteoblasts
