Bone and Joints 3 PDF

Feriha ERCAN, Ph.D. Dept. Histology and Embryology Function: Support and protection for the body and its organ A reservoir for calcium and phosphate ions. Bone is composed of : Support cells (osteoblast, osteocytes) A non-mineral matrix of collagen and GAG’s (osteoid) Inorganic mineral salts deposit...

Feriha ERCAN, Ph.D. Dept. Histology and Embryology Function: Support and protection for the body and its organ A reservoir for calcium and phosphate ions. Bone is composed of : Support cells (osteoblast, osteocytes) A non-mineral matrix of collagen and GAG’s (osteoid) Inorganic mineral salts deposited within the matrix. Remodeling cells (osteoclast). Osteoid and Bone Matrix Consists of organic (30%) and inorganic (70%) components. Organic bone matrix: Type 1 collagen (90%), proteoglycans enriched in chondroitin sulfate, keratan sulfate, hyaluronic acid, noncollagenous proteins. Noncollagenous matrix proteins are osteopontin, osteonectin, bone sialoprotein. osteocalcin, Inorganic bone matrix is represented predominantly by deposits of calcium phosphate with the crystalline characteristics of hydoxyapetite. Osteoblast The cells of Bone Osteoprogenitor cells: Stem cells bone of Osteoblasts: Synthesize the organic component of bone matrix (osteoid), mineralize it by depositing calcium and phosphate hydroxides (hydroxyapetides) Osteocytes: Inactive osteoblasts trapped in mineralized bone, lie within small cavities. Adjacent cell processes found within canaliculi are connected by gap junctions. Osteoclasts: Multinucleate cells, derived from monocytes, erode mineralized bone, localized in Howship’s lacuna Osteocytes Osteoclasts Classification of bones 1. Compact bone 2. Spongy or cancellous bone Bone marrow Types of Bone on the Basis of Microscopic Organisation of ECM 1. Lameller bone: Typical of the mature or compact bone. 2. Woven bone: Observed in the developing bone. Lameller bone consists of lamellae, largely composed of bone matrix, and osteocytes each occupying a cavity or lacuna with radiating and branching canaliculi. Canaliculi Lamel Osteocyte Lameller bone displays four distinct patterns. 1. Osteons or Haversian system 2. Interstitial lamellae 3. Outer circumferential lamellae 4. Inner circumferential lamellae Vascular channels in compact bone 1. Haversian canal 2. Volkman’s canal Periosteum Trabecular bone Blood vesels Outer circumferential lamellae Inner circumferential lamellae Interstitial bone lamellae Volkman’s canals Haversian canals Trabecular bone Compact bone Havers system Osteocytes Havers canal Osteocytes Interstitial lamel Havers canal l Osteocytes Canaliculi ossium EM micrographs of canaliculi and osteocyte Haversian canal Volkman’s canal Periosteum and Endosteum Periosteum: Inner layer: During embryonic period consists of bone-forming cells (osteoblasts), is the osteogenic layer. In the adult, periosteum contains inactive connective tissue cells that retain their osteogenic potential in case of bone injury. Outer layer: Rich in blood vessels, some of them entering Volkman’s canal, and thick anchoring collagen fibers, called Sharpey’s fibers, that penetrate the outer circumferential lamellae in the bone. Endosteum: Consists of squamous cells and connective tissue fibers covering the spongy walls hausing the bone marrow and extending into all the cavities of the bone, including the Haversian canals. Mineralization of Osteoid A glycoprotein (osteocalcin) in osteoid binds extracellular Ca++ ions, leading to a high local concentration. The enzyme alcaline phospahatase, which is abundant in osteoblasts, increases local Ca++ and PO4concentrations. Osteoblasts produce matrix vesicles, which can accumulate Ca++ and PO4ions from larger molecules. Matrix vesicles imp alcaline phospathase is produced by ostebolblst Osteoblasts Newly formed matrix vesicles Ealy mineralization of matrix vesicles increasing mineral deposition by accretion around matrix vesicles matrix vesicles with confluent mineralization Fully mineralized bone Selective Bone Resorbtion Lyosomal enzymes are released by osteoclasts. Released enzymes hydrolyse the collagenous protein and GAG’s of the bone matrix. The disrupted bone matrix yields up its attached mineral salts. Local acidic conditions result from the secretion of organic acids such as carbonic, lactic, and citric acids by osteoclasts, break up the hydroxiapetite, releasing soluble Ca++ and PO4- ions. Soluble break down products of demineralisation and protein hydrolysis may be resorbed by the osteoclast by endocytosis. Osteoclast resorbtion of bone can be stimulated by parathormone and inhibited by calcitonin. which one of the hormones below inhibit or stmulate osteoclast imp Osteoporosis and Paget’s Diseases osteoclast Normal cortical and trabecular bone osteoblast Patients wtih osteoporosis Paget’s disease Osteogenesis 1. Intramembranous bone formation: Most flat bones are formed by this way. Ossification is formed on the mesenchymal connective tissue. 2. Endochondral bone formation: Most long and short bones are developed by this way.This type of ossification occurs in two steps. 1. A miniature hyaline cartilage is formed. 2. The cartilage model continues to grow and serves as a structural scaffold for bone development. Intramembranous ossification Bone spicule Osteoblast Osteoid Bone matrix Osteocytes Mesenchyme Osteoclasts Bone spicule practical lab question Osteoblast Osteocyte Osteoid Blood vessel Mesenchyme Primary bone tissue Endochondral Ossification Early perichondrium Primitive Developing mesenchyme cartilage model Blood vessels periosteum Developing Primary bone collar (diaphysial) ossification center cortical bone Bony trabeculae Secondary (epiphysial) ossification center Hyaline cartilage Vascular invasion zone Trabecular bone Bone marrow Periosteum Resting zone Secondary ossification center Proliferative zone Hypertphophic zone Vascular invasion zone Trabecular bone Hypertphophic zone Vascular invasion zone Trabecular bone Hyaline cartilage Trabecular bone Hypertrophied and calcified zone Blood cells Chondron Hypertrophic zone Proliferative zone Resting zone Vascular invasion zone Hyaline cartilage Secondary ossification centers epiphyseal ossification center RZ PZ epiphyseal plate HZ OZ Trabecular bone Epiphyseal plate Fıgure 8-18 Copyright © McGraw-Hill Companies Summary of bone types and their organisation Type of bone Histological Features Major Locations Synonyms Woven bone, newly Irregular and random calcified arrengement of cells and collagen; lightly calcified Developing and growing bones; hard callus of bone fractures Immature bone; primary bone; bundle bone Lamellar bone, remodeled form woven bone All normal regions of adult bone Parallel bundles of collagen in thin layers (lamellae), with regularly spaced cells between; heavily calcified which one is immature bone Mature bone; secondary bone compact bone and cancelous bonr are types of lamellar bone Compact bone, 80% of all lamellar bone Parallel lamellae or Thick, outer region densely packed (beneath periosteum) osteons, with intestitial of bones lamellae Cancellous bone, 20% of all lamellar bone Interconnected thin spicules or trabeculae covered by endosteum Cortical bone Inner region of bones, Spongy bone; adjacent to marrow trabecular bone; cavities medullary bone question is from here JOINTS 1. Permit limited movement 2. Permit free movement Semi-mobile joints (synarthroses) 1. Syndesmoses: Joints between the flat bones of the skull 2. Synchondroses: Joints between ribs and sternum 3. Synostosis: In old age the support tissue forming both syndesmosis and synchondroses replaced by bone to form rigid immobile joint. Mobile joint (diarthroses) Joints that allow free movement between adjacent bones are termed synovial joints. Intervertebral disk vertebra Annulus fibrosus Nucleus fibrosus intervertebral disk vertebra Sciatica: Wear and tear on the intervertebral disks may lead to degeneration of the annulus fibrosus, with extention of the nucleus pulposus. This results in: Impaired efficency of the disk as a shock absorber. Expansion of the annulus fibrosus, causing it to bulge. Ligament Synovial joint Fibrous joint capsule Synovial cavity Articular cartilage Synovium Skeletal muscle tendon Sharpey’s fibers The internal lining of the joint capsule is a specialized secretory epithelium, the synovium, which porduces synovial fluid. Synovial membrane have two types of cells: Bone 1.Type A cells: Phagosytosis 2.Type B cells: Protein synthesis SC AC AC Arthritis: 1.Osteoarthritis 2. Rheumatoid arthritis Bone