Bone Flashcards
Organic and inorganic components to bone
- Inorganic: hydroxyapatite (Ca and P)
- Organic: type I collagen and ground substance
Compact vs Cancellous bone
- Compact: dense bone, main type in diaphysis
- Cancellous: lower density trabecular bone, found in epiphysis, short bones, and irregular bone
Both compact and cancellous bone show two type of organization
- Mature Lamellar Bone (discrete sheets of matrix)
- Woven bone: newly formed with randomly arranged components
Woven Bone
- Abundance of collagen, poorly mineralized
- Osteocytes are plentiful and random
- Important in bone development, fracture repair and bone remodeling
Mature lamellar bone
- Collagen fibers laid down in concentric lamellae
- Osteocytes are contained within lacunae in regular pattern
- Main type of bone found in adults
Osteon
- Haversian system
- Complex of concentric lamellae, central canal with artery, v and nerve, endosteum
Between successive lamellae are
Lacunae with osteocytes
Lacunae are interconnected by
Canaliculi
Dendritic processes of adjacent cells are in contact via
Gap Junctions
Osteon cells receive nutrients via
Vessels in the Central Canal
Spaces between the lattice of Trabeculae are sites of
Marrow formation
Periosteum
Outer Covering of bone
- Consists of inner cellular and outer fibrous layer
- Collagen fibers of the outer layer are continuous with adjacent bone, joints, tendons, and ligaments
Osteogenic cells
-Progenitors, develop into osteoblasts
Osteoblasts
-Secrete matrix, synthesize collagen, GAGs, glycoproteins
Osteoid
- Osteoblasts form it
- Zone of unmineralized fivers
- Osteoblasts act on this material to mineralized it, transforming it into bone
- When osteoblasts are trapped within this matrix, they become osteocytes
Osteocytes
- Cytoplasmic projections travel within canaliculi to communicate across gap junctions
- Maintain matrix and ion balance (namely Ca and P)
Internal remodeling
- Osteoclasts cut path, osteoblasts secrete matrix and fibers to form new lamellae
- Older osteons fill in central canal
Osteoclast formation and function
- Multinucleated osteoclast cells are formed from the fusion of monocytes
- Forms a ruffled border on the bone side, seals the resorption reaction edge
How osteoclast degrade bone
-Collagenase and other enzymes digest collagen and dissolve Ca
Two forms of both grown
Intramembranous and endochondral
Intramembranous ossification overview
- Bone ossified directly from mesenchyme
- Mostly flat bones, mandible, medial clavicle
- Contributes growth of short bones and the thickening of long bones
Endochondral ossification overview
- Bone ossified from cartilaginous precursor
- Derived from mesenchyme
- Endochondral growth is the norm for most of the weight bearing bones
Intramembranous Ossification steps
-bone grows within condensation of mesenchyme tissue
- ) ossification center develops (osteoblasts divide and secrete osteoid)- site of new bone formation
- ) Calcification begins (osteoblasts differentiate into osteocytes trapped in matrix) osteoblasts on the outer edge remain active
- ) development of trabeculae (spongy) by action of osteoclasts on calcified bone (bone marrow cavity formed)
- ) development of periosteum on surface of osteoblasts layer
Bone grows within what in endochondral ossification
- Cartilaginous mold
- Mold formed in mesenchyme during fetal development
Endochondral Ossification steps
- ) Hyaline cart mold secreted by chondroblasts
- ) bony collar forms through intramembranous ossification and helps maintain shape
- ) model lengthens and widens
- ) blood vessels invade, stimulating growth at the primary ossification center. Vessels fuse to create foramina
- ) Primary ossification center replaces the zone of calcified cartilage. Calcification kills chondrocytes and accelerates cartilage degen
- ) osteoclasts create and open medullary cavity as osteoblasts continue to secrete bone
- ) Secondary ossification center forms around epiphyseal vessels around the time of birth
- ) Epiphyseal line is where the primary and secondary ossification centers joint; Articular cartilage represents remnant of hyaline cartilage model
Bone growth after early development occurs at
Epiphyseal plate
Synchondrosis vs Symphysis
Synchondrosis is temporary hyaline cartilage connection between blocks of bone during development
Symphysis is permanent cartilaginous connection between bones; hyaline and fibrocartilage
Synovial joints
Complex cartilaginous joint with capsule, Articular cavity, and Articular cartilage
Articular cavity
Filled w synovial fluid derived from plasma
- Lubes and cushions joint movement
- Provides nutrients to Articular cartilage
Articular Cartilage
—Hyaline
- Reduces friction
- Absorbs shock
Osteoporosis
- Bone resorption exceeds bone formation
- Leading to decreased bone mineral density
- At risk: immobilized pt and post menopausal women
- Routinely tested for bone density using DEXA scans
Osteopetrosis
-Genetic disease characterized by dense, heavy bones “marble bones”
Causes of Osteopetrosis
- Defective proton pumps/chloride channels
- Osteoclasts lack ruffled border
- Obliteration of bone marrow cavities causes reduced blood cell formation, anemia, and WBC loss
Osteosarcoma
- Arise from osteoprogenitor cells
- Cancer originating directly from bone (primary bone tumor) is uncommon
The skeleton is often the site of
-Secondary, metastatic tumors Arising when cancer cells move into bones from malignancies in other organs
Common origination of secondary metastatic tumors
Breast, lung, prostate, kidney, thyroid
Bone Fractures
Initial repair by fibrocartilage formation, then osteogenic activity
Endosteum contains
-Osteoblasts and osteoclast
How do osteoblasts become osteocytes
-Trapped in osteoid
Bone Fracture steps
- ) hematoma forms
- ) Fibrocartilage Callus forms
- ) Hardy callus forms of WOVEN BONE by ossification
- ) Woven bone replaced by lamellar
