Bone tissue Bone is a connective tissue that is characterized by a mineralized extracellular matrix. The matrix is secreted by cells called osteocytes. Bone tissue •UNIQUE QUALITIES OF BONE •HYDROXYAPATITE: Calcium Phosphate crystals. •It prevents diffusion of metabolites. •It prevents interstitial growth -- all bone growth occurs from the periosteum. •A CANALICULAR SYSTEM: Tiny canals connect one haversian system to the other. •VASCULARITY: All bone cells are in close proximity to vessels! •APPOSITIONAL GROWTH: All growth occurs by appositional growth. •BONE RECONSTRUCTION: Bone is dynamic tissue, constantly changing shape. • Bone tissue • •LONG-BONE GROSS STRUCTURE: •DIAPHYSIS: the shaft with a medullary cavity on inside. •EPIPHYSIS: the ends. •METAPHYSIS: the site of ossification, between the diaphysis and epiphysis. •ARTICULAR CARTILAGE: hyaline cartilage covering compact bone • at the ends of long bones. It lacks perichondrium. •PERIOSTEUM: osteogenic potential around the outside. •ENDOSTEUM: lines the marrow cavity and also has osteogenic potential. • Výsledek obrázku pro bone Bone tissue •Consists of cells in lacunae, in an extracellular matrix Výsledek obrázku pro bone cells osteoblasts Bone tissue •BONE CELL TYPES •A) OSTEOPROGENITOR CELLS: • the stem-Cells of bone, on the inner lining of the periosteum and endosteum •B) OSTEOBLASTS: • secretory cells, secrete the bone matrix •ALKALINE PHOSPHATASE which calcifies the matrix. •have polarity and resemble other secretory cells •C) OSTEOCYTES: they are osteoblasts that have become trapped in their own matrix, found in lacunae, between layers of lamellae, in the matrix of cortical bone •CANALICULI: fine cytoplasmic extensions of the osteocytes running perpendicular to the haversian canals •D) OSTEOCLASTS: large, multinucleate cells derived from monocytes, have acid hydrolases, many lysosomes and are eosinophilic •HOWSHIP'S LACUNAE: the spaces for bone resorption, between the osteoclast and the bone resorption surface • • •BONE-MATRIX •COLLAGEN: Type I Collagen = 85% - 90% of total bone protein •HYDROXYAPATITE: Bone salts (Calcium Phosphate) composes the non-protein inorganic part. • Bone tissue natuerliche_image ocl41he Výsledek obrázku pro bone cells Osteoblast GER •Osteocyte lemelozní kost osteocyt v lakuně www.histology.leeds.ac.uk www.studyblue.com Osteoclast osteoclasts tchealth.com osteoblasts osteocytes Bone tissue – types • •WOVEN BONE - collagen fibers are not arrenged into lamellae and running in different directions, they form a network in gound substance, osteocytes in lacunae are situated in this network •COMPACT BONE - is recognized as: •Lamellar bone: arranged in concentric layers called lamellae, with Haversian Canals containing blood vessels in the center, often found around the outside of large bones •Spongy bone: forms trabeculae inside of bone cavity with the bone-marrow, lamellae are organized in parallel way to their surface • • Výsledek obrázku pro woven bone Výsledek obrázku pro spongy bone Compact lamellar bone •Haversian Lamellae: lamellae around central Haversian Canals •- contain blood vessels and nerves -Osteocytes are within the lamellae, with canaliculi radiating toward the central haversian canal -Volkmann's Canals: run perpendicular (transverse) to the Haversian Canals, they connect the haversian canals to each other, or to the marrow cavity • Unit_05-09A 1 – osteocyte, 2 – interstitial lamellae, 3 – haversian canal, 4 - lamellae Compact lamellar bone • Interstitial Lamellae: remnants of older haversian lamellae, they are not concentrically arranged, but lie in between the haversian systems •Circumferential Lamellae: the external and internal borders of cortical bone. • Outer Circumferential Lamellae: adjacent to the periosteum •Inner Circumferential Lamellae: adjacent to the endosteum fig09densebone plywood1 http://accessmedicine.mhmedical.com/ Lamellar compact bone (Schmorl) Spongy bone •forms trabeculae inside of bone cavity with the bone-marrow. Lamellae are organized in parallel way to their surface Výsledek obrázku pro spongy bone Výsledek obrázku pro spongy bone Lamellar spongy bone (HE) imgkid.com studydroid.com Woven bone • •WOVEN BONE: Osteocytes are uniformly distributed and randomly oriented throughout the bone !all bone starts as woven bone! •Bone first appears as little spikes called spicules, which then form trabeculae •The woven bone is reformed to make either cortical bone or spongy bone. • Výsledek obrázku pro woven bone Intramembranous ossification •Formation of bone directly from osteoblasts, with no cartilage intermediate. •Mesenchymal cells --> osteoblasts •Osteoblasts secrete the osteoid matrix •Osteoblasts then secrete alkaline phosphatase to calcify the matrix, trapping themselves in it forming Osteocytes •Some flat bones are formed by intramembranous ossification (bones of the skull, jaws, clavicula) • Enchondral ossification •Long bones are formed on a cartilage model. •GENERAL PROCESS: •Cartilage matrix is laid down •Perichondrium then becomes periosteum, when a vascular bud invades the perichondrial space, the vascular bud contains blood cells, bone marrow cells, macrophages, endothelial cells •GROWTH IN LENGTH: Occurs by proliferation of chondrocytes at the epiphyseal plates and at the primary ossification front. •GROWTH IN DIAMETER: Occurs by deposition of new bone under the periosteal collar along with simultaneous osteoclastic resorption, in order to maintain bone shape. The osteoclastic resorption is necessary to enlarge the medullary cavity. • Enchondral ossification • •PRIMARY OSSIFICATION CENTER: Occurs in the center of the diaphysis, and extends toward both epiphyses. •Thus there are two fronts of primary ossification. •Primary ossification centers close around the time of birth. Thereafter, long-bone growth occurs from the secondary ossification centers. •SECONDARY OSSIFICATION CENTER: Forms at the epiphyseal plate. •The orderly columns of chondrocytes are not seen here. •Growth occurs from the epiphysis downward, toward the epiphyseal plate. •EPIPHYSEAL CLOSURE: The end of longitudinal growth in long bone, when the primary ossification center overtakes (i.e. calcifies) the secondary ossification center, and hence long-bone growth ceases. • Enchondral ossification enos04he Intracartilaginous ossification (HES) plytka_wz Výsledek obrázku pro endochondral ossification Výsledek obrázku pro endochondral ossification Bone remodeling •The process of BONE-REMODELING, which occurs during growth and in mature bone. It explains relationship between osteoclastic and osteoblastic activity in bone-remodeling, which explains why osteoporosis is difficult to treat. •Activation: Osteoclasts are activated and begin secreting acids to resorb bone. •Resorption: Osteoclastic resorption occurs. •Reversal: Resorption stops and osteoblasts take over. •Formation: Osteoblasts form bone on the opposing surface to complete the bone reforming process. • Figure 2-2. Modeling and Remodeling Illustrations of bone modeling and remodeling. The illustration of modeling demonstrates that bone formation occurs without a link between osteoblast and osteoclast action. In the remodeling illustration, osteoblasts create an osteoid layer in the remodeling space to replace bone following osteoclast action. Figure 2-3. Bone Remodeling An illustration of activation, resorption, reversal, and formation in bone remodeling (demonstrated from left to right). In this illustration, mesenchymal stem cells become either osteoblastic stromal cells or osteoblast precursors. During the activation stage, osteoblastic stromal cells interact with hematopoietic stem cells to become osteoclasts. During resorption, osteoclasts remove bone in the remodeling space under a layer of lining cells. After a brief reversal phase (where the cell is marked “?” because it is an undefined type of cell), osteoblasts begin laying down new bone in the formation stage, which is shown as the longest of the four stages. Inside the bone, osteocytes connect to each other and to the surface of the bone. CONNECTIVE TISSUE – II: bone. Slides: Lamellar bone (95. Bone – HE or Schmorl staining) Endochondral ossification (96.) Atlas EM: Osteoblast (46) Osteocyte (47)