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• HYALINE CARTILAGE TISSUE General: •Gel GS; flexible solid, • Skeletal tissue; support • Rigidity unnecessary • Ground substance (GS) • Chondroitin sulfate • Fibers embedded in GS • Usually collagen (type II) • Chondrocytes: mature cartilage cells; • inactive; in lacuna (“tiny lake”); • Cell shriveled. • Cartilage; avascular; not innervated. • heals slowly • Often surrounded by a • Perichondrium • dense irregular CT layer 1 HYALINE CARTILAGE TISSUE • Specific characteristics • Matrix; abundant, indistinct collagen fibers. • Two reasons: • collagen fibers and the ground substance • same refractive index • GS unstained with eosinophilic dyes • Matrix looks afibrous; • Slightly smokey glass. • Hyaline = glassy. 2 HYALINE CARTILAGE TISSUE • Chondrocytes are clumped • Chondroblasts are mitotic: • divide once or twice • cells stay together. • 2-5 chondrocytes • Matrix unevenly basophilic, near clumps. • Ground substance is chondroitin sulfate, • Glycosaminoglycan: an un- branched, sulfated, polysaccharide • produced by the chondroblasts 3 HYALINE CARTILAGE TISSUE • Hyaline cartilage, most common • Nasal cartilages ; most of larynx • Trachea and bronchi • Cartilage models ; precursors to bones • Articular cartilage; modified hyaline cartilage • Ends of bones, • Slightly soft, slippery layer • for articulation. Resembles regular hyaline cartilage except: • Evenly scattered single chondrocytes. • Uniform basophilic stain. • Hyaline cartilage; matrix about 80% of tissue volume. 4 ELASTIC CARTILAGE • • • • • Elastic cartilage, next-mostcommon • Ear and epiglottis. Predominantly elastic fibers. Visible even without staining. H&E staining, matrix is lightly eosinophilic, • Due to collagen fibers • Special staining for elastic fibers. Chondrocytes are evenly distributed • Most of the tissue’s volume • Larger than those of hyaline cartilage. 5 Fibrocartilage • Third type of cartilage • Lots of collagen fibers. • Very tough • Intervertebral discs • Pubic symphysis. 6 j. COMPACT BONE (dense bone) 7 Filippo Brunelleschi Dome of the Florence Cathedral Early 15th century 8 COMPACT BONE (dense bone) General characteristics of bone: • Ground substance; rigid solid • Bone; skeletal tissue • structural support. • GS; inorganic crystalline solid • calcium phosphate and calcium carbonate • hydroxyapatite or hydroxycalcium phosphate. • Other ions; carbonate, magnesium, sulfate, and fluoride. • GS : half of the matrix. • GS unstained with H&E. 9 COMPACT BONE (dense bone) • Half matrix is collagen fibers • Bundles of parallel fibers. • Matrix formation • Collagen fibers form first • GS crystals deposited on collagen fibers • Crystals then enlarge, fill in remaining matrix space. • Collagen fibers eosinophilic, matrix bright red with H&E. 10 COMPACT BONE (dense bone) • Parallel collagen bundles • give the matrix strength. • Crystalline solid + protein fibers analogous to: • Concrete and steel rods of foundations of buildings • Fibers or rods reduce the brittleness of the ground substance • GS gives the matrix rigidity. 11 COMPACT BONE (dense bone) • Bone cells; osteocytes • metabolically active • numerous thin branching cell extensions • extend through matrix • interconnect with other osteocytes. • Cell extensions within channels called canaliculi • "tiny canals”: singular: canaliculus • Extensions form and interconnect before the matrix is well developed. canaliculi 12 Three osteocytes COMPACT BONE (dense bone) • Osteocytes; not active in bone formation • Osteoblasts, immature bone cells, produce matrix, • Osteoblasts become the osteocytes. • Osteoblasts are stimulated by Vitamin D • hormone thyrocalcitonin or calcitonin (thyroid) • Osteoblasts development • mesenchymocyte >> osteoprogenitor cell>> osteoblasts >> osteocyte • Osteoblasts become osteocytes when trapped in the matrix • Body (soma) of each osteocyte is in a lacuna. 13 COMPACT BONE (dense bone) • Bone more dynamic than cartilage • Youth, bone remodeling common • undergoing matrix deposition and erosion • Slows with age. • Osteoclasts ; bone matrix erosion. • large, multinucleate cells • eosinophilic cytoplasm • pH change erodes bone matrix • GS dissolves • stimulated by parathyroid hormone • frees Ca2+ from the matrix. 14 COMPACT BONE (dense bone) • Bone matrix is in layers; lamellae (lamella; singular) . • Lamellae are of similar thickness and lie against each other. • Each lamella: bundles of collagen fibers are parallel to each other • adjacent lamellae ; fibers in a different direction • Contributes to the overall strength of the tissue. 15 COMPACT BONE (dense bone) • Surrounding the developing bone is layer of immature bone tissue--periosteum • Periosteum similar to perichondrium • remains after growth of bone tissue • an inactive layer. http://neuromedia.neurobio.ucla.edu/campbell/bone/wp.htm 16