Bone Histology Flashcards
Lamellar bone
Mature/secondary bone
Regular parallel arrangement of collagen fibers
Most adult bones
Woven bone
Immature/primary - usually replaced by lamellar bone
Loose arrangement of collagen fibers
Lower mineral content, more cells
Forms during fracture repair/remodeling
Epiphysis
Knobby regions at end of bone
Compact bone is superficial, with spongy bone deep to surface - contains epiphyseal plat
Metaphysis
Between diaphysis and epiphysis
Consists of spongy bone
Epiphyseal line
Within metaphysis
Epiphyseal plate has fused
Medullary cavity
Cylindrical shape in diaphysis containing bone marrow
Periosteum
Dense irregular CT covering external surface. Does not cover articular surfaces
Anchored in perforating fibers
Neurovascular
Contains osteoblasts
Endosteum
CT lining of medullary cavity
Contains osteoprogenitor cells, reticular cells, CT Uber’s
Periosteum layers
Inner layer: osteoprogenitor cells next to mature bone - retain potential for bone injury and repair
Outer layer: rich in vasculature, fibroblasts and collagen fibers
Sharpey’s fibers
Sharpey’s fibers
In the outer layer of periosteum, these fibers anchor to outer circumferential lamellae
Bone matrix
Organic components: type I collagen fibers, proteoglycans, other proteins (osteocalcin, osteopontin, osteonectin)
Inorganic components: Ca hydroxyapatite, Mg, K, Na, F
Osteon
Cylindrical structures in mature compact bone - run parallel to the shaft of the bone
Canals
Central - vasculature and innervation
Perforating canals - perpendicular connections to central canal
Canaliculi - connect lacunae
Lamellae
Concentric: rings of bone around central canal
Outer circumferential - rings around periosteum
Inner circumferential - rings around endosteum
Interstitial: pieces of old osoteon that result from remodeling
Osteoprogenitor
Stem cell that produces osteoblasts
Found in endosteum and periosteum
Osteoblasts
Mesenchymal cells that produce osteoid (nonmineralized organic matrix)
Initiate and control mineralization of the osteoid
Osteocytes
Mature bone cells embedded in bone matrix
Maintain matrix
Communicate with osteoblasts to increase deposition of bone matrix
Osteoclasts
Large, multinucleated cells produced by the fusion of monocytes
Ruffled border
Remodel and reabsorb bone through H+ and lysosomal proteins
Intramembranous ossification
Bones develop from mesenchyme precursors Select bones form from this process Flat Some facial Mandible Central part of clavicle
Endochondral ossification
Begins with hyaline cartilage Produces most bones of the skeleton Bones of extremities Pectoral and pelvic girdles Pelvis, vertebrae, ends of clavicle
Reserve zone (endochondral ossification)
Primitive hyaline cartilage - responsible for lengthening - cells run
Proliferative zone ( endochondral zone)
Chondrocytes cluster parallel to growth axis
Share territorial matrix
Hypertrophic zone (endochondral ossification)
Hypertrophic chondrocytes form calcified matrix - chondrocyte apoptosis - attract vasculature - instruct bone collar
Very important zone for signaling
Vascular invasion zone (endochondral ossification)
Vasculature penetrates calcified atria (septa) - invasion of osteoprogenitor
Achondroplasia
Autosomal dominant syndrome - mutation in FGFR3 (fibroblast growth factor receptor 3) Most common form of dwarfism Shortening of long bones Small midface Altered spinal curvature
Osteomalacia
Progressive softening and bending of bone Defect results in decreased mineralization of osteoid Caused by: dietary vitamin D deficiency Lack of sun exposure GI disease (US) Signs: bone and joint pain Muscle weakness Fracture Difficulty walking and waddling gait Muscle spasms and cramps
Rickets
Juvenile osteomalacia
Defect in mineralization of cartilage in growth plate
Vitamin D deficiency, decreased absorption of calcium and phosphorus from bowels
Caclipenic - Ca deficiency
Signs of rickets
Delayed closure of fontanelles
Parietal and frontal bossing
Craniotabes (soft skull bones)
Widening of wrist and bowing of the distal radius and ulna
Progressive bowing of femur and tibia
