Exam 4 Flashcards
In regards to bone composition, hydroxyapatite is overlaid on a ____ scaffold
Collagen 1
What percentage of bone is inorganic, what portion is organic?
67% inorganic
33% organic
Name 5 noncollagenous proteins found in bone. (Note that these are also found in dentin)
Bone sialoprotein
Osteopontin
Osteocalcin
Osteonectin
Matrix extracellular phosphoglycoprotein
Name four physiological roles of bone
Structural
Calcium homeostasis
Reservoir for growth factors in tissue repair
Contains both hematopoietic and mesenchymal progenitor cell populations
Describe the macrostructure of bone
Outer layer of dense compact (cortical) bone with an inner cavity
Inner cavity contains marrow (red or yellow) and cancellous (trabecular) bone
Bone is highly vascular, with a network of blood vessels.
What are the 3 organizational units of the macrostructure of compact bone?
Circumferential: outer ring of bone tissue
Concentric lamellae: intact osteons
Interstitial lamellae: fill space between concentric lamellae: former concentric lamellae
Why are interstitial lamellae half-circle in shape?
The bones are constantly being remodeled. Half-circle osteons are osteons that have diminished and are beginning to be replaced.
Osteons are formed around ____ canals
Haversian
Osteons are the basic functional units of compact bone. They form cylinders running ____ to the long axis of bone. They are formed from ____ lamellae. They are build around a canal called a ___.
Parallel
Concentric
Haversian canal
____ canals connect Haversian canals, linking osteons.
Volkmann
Cancellous bone is spongy bone, much less densely arranged than compact bone. Where is this bone found? What are its functions?
Found at the ends of long bones, in apposition to joints and is associated with the marrow spaces
Functions to provide structural support for marrow tissues and it is the site of blood cell production, also supports mesenchymal and hematopoietic progenitor cell populations
Note that this bone type is highly vascularized.
What is the periosteum?
Connective tissue layer attached to the outer layer surface of bone by sharpey’s fibers.
What are the two layers of the periosteum?
Outer fibrous layer and inner layer in apposition to the bone surface. The inner layer is both highly cellular and vascularized.
Note that the inner layer is involved in growth and repair.
What is the endosteum?
Loose connective tissue covering the inner surface of both cancellous and compact bone.
Separates the marrow from the bone. Poorly defined histologically.
What are the three different types of bone cells? Describe them.
Osteoblasts: bone forming cells with a mesenchymal origin (form a premineralized matrix)
Osteocytes: bone cells, which are actually encapsulated osteoblasts
Osteoclasts: cells which break down tissue. Hematopoietic in origin.
Describe the origin of osteoblasts and osteoclasts
Osteoblasts: mesenchymal origin
Osteoclasts: hematopoietic origin (they are kinda like bone macrophages)
Osteoblasts are ___-nucleated cells which synthesize ___ matrix. They differentiate in response to a cascade of growth factors and play a role in both bone formation and repair. Osteoblasts do not form complexes, rather they communicate with one another through ___
Mono
Osteoid (unmineralized collagen matrix)
Gap junctions
How is the osteoid production of osteoblasts similar to odontoblasts?
The produce and secrete collagen and non collagenous proteins in vesicles
Also note that they secrete growth factors in osteoid matrix
After bone formation, osteoblasts flatten, forming ____ cells
Bone lining
What are the cells that are osteoblasts which are embedded into the bone matrix and are considered the terminal differentiation of osteoblasts?
Osteocytes
True or false… osteocytes form interconnected lacunae in the bone tissue. They have cellular processes which interact with surrounding bone tissue: mechano-transduction, coordination of odonto/osteoclast activity and possibly work in conjunction with bone lining cells
True
True or false… osteoclasts are mono nucleated cells that result from fusion of monocytes
False. Although they do result from the fusion of monocytes, they are multi-nucleated cells
Osteoclasts are responsible for the resorption of bone and are activated in inflammation by ___ and ___
IL-1b
TNF-a
What is TRAP and what is it used for? What are TRAP positive cells?
Tartrate resistant acid phosphatase
It is a histological marker used to identify osteoclasts
TRAP positive cells are osteoclasts
Describe how osteoclasts resorb bone.
Osteoclasts attach to the surface of bone by integrin, cytoplasm adjacent to surface is rich in talin, actin, and viniculin (helps form a tight seal).
This creates a ‘ruffled border’ in apposition to bone to form resorption pits (Howship’s lacunae)
Within Howship’s lacunae, osteoclasts secrete hydrogen ions and matrix degrading enzymes to demineralize bone.
The bone matrix undergoes transcytosis through the osteoclast to be released through the opposite side
What is lamina limitans?
It is the zone between Howship’s lacunae and intact bone. (This is the surface where bone is being degraded by the stuff released from osteoclasts)
Osteoblasts and osteoclasts are supplied by ___ cell populations, then differentiate in response to signaling cascades. Bone cell recruitment also results from trigging by ___, ___, and ____.
Progenitor
Tissue damage
Inflammation
Repair signals
Bone formation is controlled by complex interactions between osteoblasts and osteoclasts through a balance of synthetic and resorptive signals. Osteoblasts regulate osteoclast function through the ____ system. Describe this system.
RANK-RANKL-OPG
RANKL- receptor activated nuclear factor kb ligand: osteoblasts
RANK - receptor activated nuclear factor kb: osteoclasts
OPG - osteoprotegerin: produced by osteoblasts, binds RANKL
If RANKL (osteoblasts) binds to RANK (osteoclasts), resorption occurs. If osteoblasts secrete OPG, it binds to RANKL to prevent binding of RANKL to RANK, thus preventing resorption.
In endochondral formation, bone is formed on a ___ cartilage pattern. It causes ___ cells to condense into ____. When collagen is secreted, it mineralizes and is broken down by ____, allowing penetration of vasculature.
Hyaline
Mesenchymal
Chondrocytes
Chondroclasts
In endochondral formation, once vasculature is formed, ___ cells come which differentiate into ___.
Mesenchymal
Osteoblasts
In endochondral formation, bone matrix surrounds remaining mineralized collagen, forming ____ which make up the ____
Mixed spicules
Primary spongiosa
In endochondral ossification, osteoclasts gradually remove mineralized cartilage to develop the inner ____. Also, secondary growth centers form in the ___ of some long bones.
Marrow cavity
Epiphyses
In intramembranous ossification, mesenchymal cells condense in ____, differentiating into ___ and forming an ossification center. ___ is secreted into the connective tissue matrix and is penetrated by ____, which results of rapid formation of mineralized woven bone. Woven bone is remodeled into mature ___ bone with a collar of cortical bone around it.
Fibrous connective tissue
Osteoblasts
Osteoid
Blood vessels
Trabecular
Sutural bone growth is effectively the fusion of skull plates. Sutures are ___ bands between the plates. Inner ___ layer, associated with the ___ ,meets with the outer ___ layer to join the sutures together. The advantage to sutures is that it gives flex to the skull as bone formation proceeds. (Ultimately the sutures are replaced with bone)
Fibrous connective tissue
Cambian
Periosteum
Capsular
Bone is continually destroyed and reformed. Children turnover ~___% of their bone per year whereas adults turn over ___% of cortical and ___% trabecular per year
30-100
5
15
Most bone is deposited around the ____ and resorbed from the ____. This allows the marrow cavity to grow in size
Periosteum (outside)
Endosteum (inside)
Describe the bone remodeling and repair of cortical bone
Primary osteons are replaced by secondary osteons which are replaced by tertiary osteons, allowing bone growth
What are the 4 general phases of tissue repair?
Hemostasis: clot formation
Inflammation: infiltration of immune cells and initiation of repair
Reparative phase (proliferation): migration of cells, formation of granulation tissue
Wound contraction and scarring
What is hemostasis? What are its primary and secondary goals?
Hemostasis transition of blood from a liquid to a fibrillar gel
Primary goal: stop the bleeding
Secondary goal: initiation of healing
In hemostasis, what leads to the coagulation cascade? Clot unites edges of wound, and the ___ provides a scaffold for future cell migration and repair
Disruption of platelets
Fibrin
The clot formed in the oral cavity is different than in other parts of the body. How?
It is softer and more easily detached
What is primary hemostasis?
Vascular constriction and initial platelet plug in a damaged blood vessel
How is primary hemostasis initiated?
Exposure of collagen in ‘subendothelium’ (normally separate from the lumen) to circulate Von Wilebrand Factor
What does Von willebrand factor do in primary hemostasis?
Von wilebrand factor causes platelet aggregation by interacting with platelet surface proteins
Note that platelets can also bind collagen directly via GPVI and a2b2 integrin
Platelets activate and dump out tons of preformed cytoplasmic vesicles containing ___, ___, ___, and platelet agonists ___ and ___. ___ anchors platelets together
More Von willebrand factor
Fibrinogen
Coagulation factors V and XIII
Serotonin
ADP
Fibrinogen
What does fibrinogen do?
Anchors platelets together
True or false… secondary hemostasis always occurs after primary hemostasis
False.. it may occur simultaneously with primary hemostasis or just after
Secondary hemostasis (blood coagulation) is a fairly complex cascade involving extrinsic and intrinsic pathways. Describe each of these pathways
Extrinsic: involved tissue factors which are. Not normally found in blood. factor VII and tissue factor interactions (found around(or on) fibroblasts), initiate the cascade.
Intrinsic: involves factors found in the blood. initiated by damaged endothelium (collagen exposure)
The ultimate goal of secondary hemostasis is to convert ___ into ___ which in turn converts soluble ___ into insoluble ___. Many of the steps involved in secondary hemostasis involve ___.
Prothrombin into thrombin
Fibrinogen into fibrin
Calcium
Fibrin cross-links to form a mesh, trapping red and white cells, resulting in a clot.
Which, the intrinsic or extrinsic pathway of blood coagulation involves factor VIII?
Intrinsic
In the reparative phase of hemostasis, ____ of adjacent cells occurs (epithelium). This will allow epithelial cell migration, which is…
Cell migration under fibrin clot occurs which creates a highly cellular ___ tissue
Mobilization
Epithelial cell migration: formation of new basal lamina, redistribution of integrin receptors, and formation of new hemidesmosomes. Eventually this forms a thin cover over the wound
Granulation
In the reparative phase, local and recruited ____proliferate in the wound. ___ production begins to fill the defect, forming a scaffold.
Fibroblasts
Collagen
In the reparative phase, endothelial cells proliferate and angiogenesis occurs. This occurs due to what three signaling factors?
TGF-b
VEGF
FGF-2
What are myofibroblasts? What are they involved in?
They are specialized fibroblasts with increased actin and myosin that function to close the wound
They align around wound, form cell junctions, and attach to connective tissue fibril around wound and draw wound edges together
True or false… generally, there is no scarring of oral mucosa
True. But no one really knows why
In periodontal disease bacteria induce inflammation at gingival margins, causing destruction of connective tissues. The formation of pocket epithelium occurs due to…
Apical migration of junctional epithelium
___ can arrest the spread of infection into periodontal tissues
Fibrosis
If the source of inflammation in periodontal disease is removed, the ___ stimulates reattachment of connective tissues
Fibrin clot
Pockets of about __mm or less can regain attachment
5
True or false… the repair mechanism of the PDL is basically the same as skin
True, however immediate remodeling of collagen by ligament fibroblasts = no scarring
In guided tissue regeneration, what is the purpose of using a membrane?
To prevent epithelial invasion, to allow connective tissue reattachment
What are the three primary zones of dental caries?
1) surface and body: surface zone re-mineralizes, body is the primary zone of demineralization
2) dark zone: zone of increasing demineralization
3) translucent zone: leading edge, caused by micro-pores which form in the enamel rod boundaries.
Note that caries are dynamic: continual de-mineralization and re-mineralization, but a net loss of demineralization
Reactionary dentin is formed due to a ___ stimulus while reparative dentin is formed due to a ___ stimulus
Mild
Strong