Ignacio's Lectures Flashcards
Osteocytes
- Osteoblasts buried in bone matrix
- Form osteocyte network - syncytium
- Sense & translate mechanical strains into biochemical signals (initiate bone loss or gain)
Bone Minerals
Ca++ & Phosphorus arranged in hydroxyapatite crystals deposited in gap regions of collagen fibers
Osteogenic (Cambium) Layer
- Inner layer of cortical bone
- Composed of osteoprogenitor cells (stem cells capable of producing osteoblasts)
Endochondral Ossification
1a. Reserve/Resting Zone
Source of chondrocytes for the proliferating zone
Canaliculi
- Minute canals radiating from lacuna
- Communicate w/ nearby lacunae
Interstitial Lamellae
Angular lamellae btween haversian systems
Indications for Tooth Extraction
- Mobile teeth
- Crowding of teeth
- Retained teeth
- Teeth in line of fracture
- Teeth destroyed by disease
- Endodontically diseased teeth (dental pulp, aka root canals)
Intercellular/Ground Substance
- Glycosaminoglycans (GAGs) → Aggrecan
- Hyaluronic acid
- Chondroitin sulfate
- Keratin sulfate
Periosteum
- Connective tissue that lines external surface of cortical bone (except at articular cartilage sites)
- Highly vascularized
- Outer fibrous layer
- Inner osteogenic (cambium) layer
- Contains osteoblasts during growth & development
Nutritional Osteodystrophy
Low Ca++, High P diet → hypocalcemia → Incr. PTH → Incr. osteoclast resorption, Decr. osteoblast formation, fibrous tissue replaces bone
Blood Flow to Cortical Bone
- Centripetal Flow (going in)
- outer 1/3 of heavy periosteal attachements supplied by periosteal a.
- Centrifugal Flow (going out)
- inner 2/3 supplied by nutrient a.
Interstitial Cartilage Growth
Division of chrondrocytes within lacunae & synthesis of new cartilage matrix
(cartilage expands from within)
Fibrocartilage
- Irregular, dense, fibrous tissue
- Dispersed, encapsulated chondrocytes
- Large bundles of Type I collagen fibers
- Resist compression & shear forces
- High tensile strength
- No perichondrium
- Annulus fibrosis of IVD, menisci, insertions of tendons & ligaments
Retained Tooth
Permanent tooth bud does not grow immeadiately beneath deciduous (baby) tooth & does not casuse roots of deciduous tooth to be resorbed
Mature (Lamellar) Bone
- Matrix organized into arrays of lamellae
- Extracellular matrix >>> cells
Endochondral Ossification
1b. Proliferative Zone
Chondrocytes:
- multiply
- accumulate glycogen
- produce matrix
- arrange in longitudinal columns (stack like coins)
Maloclusion
Failure of upper & lower teeth to interdigitate properly
Endochondral Ossification
- Primary Ossification Center Formation
- Blood vessels of metaphysis invade calcified catrilage
- Formation of primary ossification center
- Osteoblasts produce bone trabeculae in diaphysis
Hyaline Cartilage
- Matrix rich in type II collagen fibers
- Fetal skeleton, growth plate, articular cartilage, larynx, trachea
- Appositional or Interstitial growth
- Avascular
- Allographs successful (immune cells can’t get to it)
- Limited regenerative properties
Periodontitis/Periodontal Disease
- Bacterial film on tooth produce acids & enzymes → damage enamel, subadjacent gingival tissue, periodontal ligament
- Plaque mineralizes → atrophy & inflammation of gingival eptithelium
- Alveolar bone loss
Osteoporosis
- Low bone mass (resorption > formation)
- Predisposes to fractures
- Not big issue in vet med
Factors Imparing Bone Fracture Healing
- Advanced age
- Poor nutritional status
- Inadequate food supply
- Soft tissue between fractured ends of bone
- Inadequate immobilization
- Infection @ fracture site
Zones of Endochondral Ossification
- Reserve/Resting zone
- Proliferative Zone
- Hypertrophic Zone
- Maturation
- Degeneration
- Calcification
Bone Remodeling
Resorption (osteoclasts) → Reversal (prep bone surface) → Formation (osteoblasts) → Resting
- All steps occur on same surface
- Does NOT result in change in shape or position of bone
Cutter Cone
- Occurs in direct/primary bone healing
- Bone remodeling
- Osteoclasts cross the fracture site w/ osteoblasts following behind to lay down concentric lamellae (osteons)
Fibrous Osteodystrophy
- Incr. osteoclastic resorption of bone & replacement by fibrous tissue
- Factors: Hyperparathyroidism (primary < secondary)
- Signs: deformities, lameness, pathologic fractures
- “Rubber Jaw”
- “Popeye Long Bone”
Articular Cartilage
- Hyaline cartilage
- Within joint spaces
- NOT covered by perichondrium
- Interstitial growth
- Nutrients received via synovial fluid
Bone Resorption
- Decalcification of matrix: acidification within subosteoclastic compartment
- Digestion of organic components of matrix (collagen, PGs): lysosomal acid hydrolases (cathepsins)
Osteochondrosis Dissecans (OCD)
- Articular epiphysis complex dysplasia
- Clefts in retained cartilage w/ subsequent fracture of overlying cartilage
- Pain, effusion, lameness, synovitis
- Dogs (shoulder), horse (tarsus), pig (femur)
- Leads to DJD
Endochondral Ossification
- Formation of Compact Bone
- Cartilage is entirely replaced by bone
- EXCEPT:
- epiphyseal growth plate
- articular cartilage
- EXCEPT:
Haversian Systems/Osteons
Concentric rings of matrix surrounding a circular, vascular canal
Appositional Cartilage Growth
- Deposition of new cartilage matrix by chrondroblast @ perichondrium (surface)
- Growth via widening of bones
Prognathia
- Maloclussion
- Protrusion of lower jaw
- “Undershot”
Appendicular Bones
- Thoracic limbs
- Pelvic limbs
Endochondral Ossification
- Medullary Cavity Development
- Bone collar thickens, lengthens
- Mature bone produced from woven bone
- remodeling (bone formation & resorption)
- Medullary cavity developes via osteoclast resorption
- Bone marrow generated
Fraction Classification: Pattern
Inner Circumferential Lamellae
Cortical lamellae that extend completely around the entire cortex just beneath the endosteum
Endochondral Ossification
1c. Hypertrophic Zone
Chondrocytes secrete macromolecules that modify matrix to allow capillary invasion and initiate matrix mineralization
Indirect/Sencondary Bone Healing
- Occurs w/ inadequate fixation & stabilization for primary bone healing
- Requires fibrous/cartilagenous callus (bridge)
Endochondral Ossification
- Calcification of Cartilage
- Formation of woven bone collar
- Blood vessels supply perichondrium
- Osteoblast differentiation
Direct/Primary Bone Healing
- Does NOT require callus formation
- Occurs w/ absolute fracture stability
- Direct osteonal remodeling (“cutter cone”)
Chondrodystrophy
- Disproportionate dwarfs (basset hounds, dauschunds)
- Primary lesion in growth plate and/or articular epiphysis complex
- Random or selected mutations
Vascular canals of Haversian System (Osteon)
- Haversian canals (center of osteon)
- Volkmann’s/communicating canals (connect adjacent Haversian canals)
- Perforating canals (penetrate from periosteum & endosteum)
Chondrocytes
- Mature cartilage cells
- Embedded in matrix within lacunae
Bone Neoplasia
- Primary
- Osteosarcoma
- Secondary
- Metastasis to other regions (breasts, prostate, lungs)
Brachydontic Teeth
- Do NOT grow continuously
- Humans, carnivores, pigs
- Crown covered in enamel only
- Root covered in cementum only
Fibrils
- Collagen (and sometimes elastin) fibers
- Arranged in 3D felt-like pattern
- Part of matrix
Avascular (atrophic) Nonunion
- Failure of fracture to heal AND lack of callus formation
- Rigid internal fixation in combo w/ method to stimulate fracture healing
Deciduous Teeth
Baby teeth
Matrix
- Intercellular/ground substance
- Fibrils (collagen fibers)
Inflammation/Necrosis of Bone
- Infectious: osteomyelitis
- Non-infectious: hypertrophic osteodystrophy
- Aseptic necrosis of bone (Legg-Calve-Perthes disease)
Osteoblasts
- Derived from mesenchymal stem cells
- Bone formation
- Produced bone matrix (osteoid)
- Initiate mineralization of matrix
- Initiate resorption of matrix by osteoclasts
- Single nucleus
- Occur in groups along bone surfaces
Vascular Nonunion
- Callus formation but failure of fracture to heal
- Responds well to rigid internal fixation
Interconvertible Cells
Cell can be converted to another cell type
Methods to Stimulate Bone Fracture Healing
- Cancellous bone autograft
- Bone marrow cell injection
- Bone graft substitute
- Bone morphogenetic protein (BMP)
- Electrical/Ultraound stimulation
- Shockwave therapy
Outer Circumferential Lamellae
Cortical lamellae that extend completely around the entire cortex just beneath the periosteum
Bone Modeling
- Bone resorption: endocortical surface
- Bone formation: periosteal surface
Axial Bones
- Head
- Vertebrae
- Ribs
- Sternum
Fraction Classification: Relation to External Environment
- Simple/closed
- Compound/open
Elastic Cartilage
- High concentration of elastic fibers in ground substance
- Closely packed chrondrocytes (no isogenic groups)
- Does NOT calcify
- External ear, auditory tube, epiglottis
Osteoclasts
- Derived from hematopoietic stem cells
- Multinucleated
- Bone resorption
- Resorption surface: Howship’s lacuna, resorption bays
- Brush border adjacent to resorbed surface
- Extensive membrane infolding @ bone/osteoclast interface
- Activation: osteoblasts & bone marrow stromal cells
- Decr. activity: estrogen, calcitonin
- Incr. activity: PTH
Endochondral Ossification
- Secondary Ossification Center Formation
- In epiphysis
- late in fetal development
- no medullary cavity occurs
Arterial Supply to Long Bones
- Nutrient artery (marrow cavity)
- Metaphyseal artery
- Epiphyseal artery
- Periosteal artery
Frature Classification: Etiology
- Traumatic
- Pathologic
- Stress
Bone Regions (___physes)
Hypsodontic Teeth
- Grow throughout life
- Horses, ruminants
- Entire tooth encased in cementum, then enamel
Bone Functions
- Locomotion
- Support
- Attachment site for muscle tendons
- Mineral homeostasis
- Hematopoiesis (blood cell production)
Cancellous Bone
- AKA spongy or trabecular bone
- Made up of trabeculae arranged in lamellae
- Withstands mechanical stress applied to bone
Endosteum
- Lines all internal surfaces of bone, including;
- Endocortical surface of cortical bone
- Surfaces of cancellous bone
- Canls of cortical bone
- Loose connective tissue
- Squamous cell lining (osteoprogenitor cells)
Chondroblasts
- Immature cartilage cells
- Secrete extracellular matrix
- NOT imprisoned in lacunae
Osteomalacia/Rickets
- O: adults, only bone affected
- R: growing skeleton, bone & cartilage affected
- Failure of mineralization → bone deformities, fracture, bone pain
- Factors: Vit. D or phosphorus deficiency
- Rachitic rosary of ribs (focal thickening of growth plates)
Cement/Reversal Lines
Thin lines of uncalcified matrix along margins of haversian & interstitial systems
Brachygnathia
- Maloclussion
- Shorter lower jaw
- “Overshot”
Flat Bone
- Develop via intramembranous ossification
- osteoblasts produce bone directly
- No cartilage precursors
- Ex. skull
Endochondral Ossification
- Mature Bone
- Cortical & cancellous bone development
- Epiphyseal growth plate fused
- Perichondrium → periosteum
Healing of (tooth) Extraction Socket
Clot formation → repair phase → initiation of bone formation → woven bone → lamellar bone
Bone Lining Cells
- Cover resting bone surfaces
- Communicate w/ osteocytes via canaliculi
- Regulation of Ca++ flow from bone to extracell. fluid
- Can convert to osteoblasts w/ hormonal/mechanical stimuli
Fracture Classification: Displacement
- Undisplaced
- Displaced
- Translation (shift)
- Angulation (tilt)
- Rotation (twist)
Osteochondrosis (OD)
- Degernerative process of cartilage
- Involves growth plate and/or articular epiphysis complex
- Retention of growth cartilage (failed to mineralize) → ischemic necrosis
- Lameness, pain
- Young animals
- Large dog breeds (shoulder, elbow, tarsus), horses, cattle, poultry
Cortical Bone
- AKA compact bone
- Harder, outer layer of bone
- Made up of osteons
Renal Fibrous Osteodystrophy
- Decr. glomerular function → hyperphosphatemia
- Decr. activation of 1,2-D3 → Decr. Ca++ absorption
→Incr. PTH → Incr. ostroclast resorption, Decr. osteoblast bone formation, fibrous tissue replaces bone
