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BONE TISSUE Textus Osseus BONE TISSUE Textus osseus Eva Mechírová, Zuzana Fagová Training for Students of MediTec project 1. – 15. 9. 2019 UPJŠ, Košice, Slovakia - specialized connective tissue for support and protection - composition: - cells - mineralized intercellular matrix – bone matrix Function: - supports and protects fragile tissues and organs - harbours the bone marrow - protects vital organs in the cranial and thoracic cavities - serves for storing of calcium, phosphate and other ions - body movement together with skeletal muscle contraction Histological composition of the bone tissue 1. Bone matrix – intercellular substance a. Inorganic components b. Organic components: Fibers Amorphous ground substance 2. Cells a. Osteoprogenitor cells (preosteoblasts) b. Osteoblasts (bone forming cells) c. Osteocytes (inactive osteoblast) d. Osteoclasts (bone resorbing cells) 1.Bone matrix – intercellular substance a. Inorganic components → Ca, P, Mg, K, Na → hyproxyapatite crystals (65%) crystals lie alongside collagen fibrils and are surrounded by amorphous ground substance b. Organic components: Fibers → collagen fibers (collagen type I) ! Amorphous ground substance → GAG, PG, structural GP chondroitin sulfate osteonectin sialoprotein osteocalcin This composition gives rigidity and resistance to bone tissue Bone tissue CELLS Osteoprogenitor cells - mesenchymal origin Cells mononuclear phagocyte - Character of stem cells: system – osteoclasts proliferation and differentiation - originated from hemopoietic - become active – during growth, progenitor cells fracture repair - break down calcified matrix Osteoblasts – active, produce osteoid - regulate bone mineralization Osteocytes – cells of mineralized bone tissue - remained as terminally differentiated cells for years - reactivation Osteoblasts – line endosteal and periosteal surfaces ( epitheloid layer) - cytoplasm : basophilic, granular endoplasmic reticulum, Golgi apparatus, light euchromatic nucleus - high proteosynthetic activity- produce alkaline fosfatase (membrane limited vesicles) that neutralise the inhibitory effect of pyrophosphate, - produce collagen type I (95%), GAG, proteoglycans, glycoproteins - polarized cell – nucleus opposite the bone tissue FUNCTION : 1) synthesis of organic components of bone matrix (growth, response to fracture, remodeling of bone) 2) regulate minerelization of bone matrix 3) regulate activity of osteoclasts cuboidal cells with basophilic line endosteal and periosteal cytoplasm (proteosynthesis) surfaces - form a single layer deposited unmineralized organic matrix – mineralized bone osteoid – produced at the surface when tissue new bone is required Osteocytes - are differentiated osteoblasts embeded in mineralized matrix- differentiated cells for years involoved in maintening of bone matrix - oval shape with long processes - occupy small cavities – lacunae - nucleus with higher content of heterochromatin - reduced GER,GA osteocytes lie in the lacunae between or inside the lamellae of mineralized matrix -metabolites are unable to diffuse through calcified matrix, the exchanges between osteocytes and blood capillaries depend on communication through the cannaliculi ossium (100µm) Osteocyte (EM) Osteoclasts: monocyto-macrophage system - motile cells situated in Howships lacunae – on the surface of bone tissue - acidofilic cytoplasm, 5-50 nuclei on the outer surface - on the inner surface many cytoplasmic processes, ruffled border – enlarge resorptive area Function: - synthesis of collagenases, acidic phophatases = proteolytic enzymes - resorption of bone tissue – extracellular braek down Osteoclasts – derived from fusion of monocytes – 5-50 nuclei, ø 40 µm 5-50 nuclei • abundant mitochondria • acidophilic cytoplasm • poor GER •well developed Golgi compl. • high number of lysosomes foamy look osteoclast is a highly polarized cell situated in superficial concavity of bone – Howship lacuna Types of bone tissue 1. primary woven bone tissue-immature ► formed during embryonic develop. -primary bone tissue is replaced by lamellar, secondary bone tissue 2. secondary lamellar bone tissue – mature compact bone tissue spongy bone tissue (trabecular) 1) PRIMARY- woven-immature bone tissue - In growing skeleton, particularly in embryo and fetus - In adults- during rapid bone remodeling (post-fracture repair) - near the sutures of the flat bones of the skull, tooth sockets a) bundles of collagen fibres are irregular b) numerous bone cells c) irregular lacunae ossium d) less mineralized e) no lamellae are present!! aaaaaa 2) SECONDARY BONE tissue - lamellar - mature • a) collagen fibers in lamellae are paralelly arranged • b) embedded in mineralized bone matrix • c) form concentric layers -lamellae thick 3-7 µm • d) osteocytes occupy the cavities -lacunae at the outer margin of the lamellae, or inside of lamellae TYPES OF LAMELLAR BONE TISSUE: 1. Compact – on the surface of diaphysis of long bones on the surface of flat or irregular bones 2. Spongy - in epiphysis - 80% of its volume made up of cavities filled with bone marrow Spongy bone tissue: a) network of irregular lamellae of bone tissue 100-300 µm thick called trabeculae b) bone marrow between trabeculae d) no Haversian systems SPONGY BONE TISSUE Compact bone tissue on the surface of a long bone 4 systems of lamellae: 1.Outer circumferential lamellae 2.Haversian systems (osteons) 3. Interstitial lamellae 4.Inner circumferential lamellae OSTEON – HAVERSIAN SYSTEM – circularly arranged lamelae of bone tissue central canal - Haversian, surrounded by 4-20 concentric lamellae of bone tissue Haversian canal contains - blood vessels, nerves and loose connective tissue -between the lamellae lie the osteocytes in lacunae ossium - long cytoplasmic processes run in canaliculi ossium cementum on the surface of osteon lacunae lamellae canaliculi ossium interstitial lamellae Haversian canal cementum lacunae osteon Compact lamellar bone tissue Formation of lamellae in osteons Osteoblast Osteoid HaversovHaversiankan canalál Periosteum – covers outer surface of the bones • outer layer: dense connective tissue ; Sharpey´s fibers (collagen type I) • inner layer: osteoprogenitor cells – spindle shaped – quiescent form activation during growth and repair of bone Endosteum - lines inner surface of the bones: • lines bone marrow cavity • lines Haversian canal Thin layer of connective tissue and osteoprogenitor cells NUTRITION OF THE BONE Blood vessels from periosteum & endosteum – run through horizontal Volkmann´s canals – vertical Haversian´s canals – canaliculi ossium (osteocytic processes) Haversian canals communicate with the marrow cavity, the periosteum, and each other through horizontal or oblique Volkmann canals Volkmann's canals run at right angle to the Haversian canals BONE as an organ is composed of: bone tissue cartilage blood vessels connective tissue bone marrow Classification of bones: long bones – epiphysis, diaphysis short bones flat bones of the skull (diploë) irregular bones.
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