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WHERE AM I? Online Anatomy Module 1 INTRO & TERMS CELL EPITHELIUM CARTILAGE MUSCLE NERVOUS SYSTEM AXIAL SKELETON APPENDICULAR SKELETON MUSCLES EMBRYOLOGY SKELETON & DISTINCT CARTILAGE ‘SKELETONS’ Ear cartilage Nasal cartilage Cartilage participates as pieces that develop, and stay attached to the skeleton Xiphoid process an extension to the breast-bone Other cartilages act as separate skeletal elements in their own right: supporting the larynx (voice-box) [feel its firmness on yourself] and the trachea (windpipe) & bronchi CARTILAGE & ITS SITES Ears Nose Airway Cartilage is a firm, but flexible, pressure-resisting tissue, needed to support and connect other tissues and structures Ends of ribs Spine disks Joints CARTILAGES: Technical names Ears Auricular cartilage Nose Nasal/septal cartilage Airway Laryngeal & tracheal cartilages Ends of ribs Costal cartilages Spine disks Intervertebral disks Joints Articular cartilages CARTILAGE Cartilage cells introduce to the tissue resistance to pressure & an ability to recover shape , principally by aggregated proteoglycans able avidly to bind water. The PGs themselves are held in place by a meshwork of fine collagen fibrils (tiny fibers). Chondrocytes make a Matrix of Collagen II fibril meshwork trapping aggregated Proteoglycans PGs PG L PGs bind L - Link protein L L H2O aggregating backbone of HYALURONAN PG CARTILAGE Cartilage cells introduce to the tissue resistance to pressure & an ability to recover shape, principally by aggregated proteoglycans able avidly to bind water. The PGs themselves are held in place by a meshwork of fine collagen fibrils. Fibrocartilage is dense fibrous tissue with chondrocytes & their PGs substituted for fibroblasts Intervertebral disk is under pressure, but has tensile strength vertebral endplate to resist bursting and pull fibrocartilage of annulus fibrosus nucleus pulposus CARTILAGE Fibrocartilage is dense fibrous tissue with chondrocytes & their PGs substituted for fibroblasts Intervertebral disk is under pressure, but has tensile strength to resist bursting and pull fibrocartilage of annulus fibrosus Fibril orientation differs from one fibrous layer to nucleus pulposus the next CARTILAGE Intervertebral disk is under pressure, but usually has enough tensile strength to resist bursting and pull, however fibrocartilage of annulus fibrosus nucleus pulposus Herniated/ruptured disk pressing on nerve leaving spinal canal, e.g., causing sciatica JOINT/ARTICULAR CARTILAGE resilient, thin, lubricated, attached, living, nourished, modifiable, vulnerable Bone Joint capsule Muscle JOINT TERMS SYNOVIUM loose connective tissue { lining cells Joint capsule j o i n t . c a v i t y Joint cartilage Spongy subchondral absorbs and bone absorbs and spreads load directs load to shaft SKELETON & CARTILAGE Cartilage provides some flexibility & recovery of shape at critical places Cartilage participates as pieces that develop, and stay attached to the skeleton Other cartilage develops with bones (indeed, it precedes the bone), then remains at the ends to make the joint surface or articular cartilage Facial and skull vault/dome bones form with negligible cartilage present SKELETAL DEVELOPMENT Skeletal piece of hyaline cartilage Grows by internal expansion and from the surface Cell enlargement/hypertrophy Matrix calcification Calcified cartilage can be resorbed like bone, and be attached to bone selective erosion into mineralized cartilage LATER ENDOCHONDRAL OSSIFICATION Articular cartilage Growth/epiphyseal plate Secondary ossification centers - + Shaft bone grows by deposition on the outside, with mild resorption on the inside surface, plus osteonal remodelling in the interior Bone would be larger than in the previous view JOINT CARTILAGE Matrix Chondrocytes in holes/lacunae layer of mineralized cartilage for attachment to bone JOINT CARTILAGE Chondrocytes make a Matrix of Collagen II fibril meshwork trapping aggregated Proteoglycans PGs PG L - Link protein L L L PGs bind H O aggregating backbone of HYALURONAN 2 PG PROTEOGLYCAN STRUCTURE & H2O-BINDING Sugar side-chains of repeating pairs (disaccharides) SO4 SO4 } H2O SO4 -XL-GA-GU-GA-GU-GA-GU-GA-GUCore protein Side chains bear coo H2O -binding charged groups which mutually repel, but cannot disperse because of O2 bonds & anchorage to the core protein ARTICULAR CARTILAGE NUTRITION Nutrition SYNOVIAL FLUID Lubrication Why via synovial fluid? #1 Load-bearing surface, therefore vessels would not survive Nutrition from marrow blocked by mineralized-cartilage layer JOINT/ARTICULAR CARTILAGE Resilient - Meshwork loaded with H2O-trapping huge molecules Lubricated - Synovial fluid & its special molecules Attached - Via mineralized lowest layer to subchondral bone Living - Matrix allows diffusion to chondrocytes in lacunae Nourished - From synovial vessels via synovial fluid Modifiable - Cells continue to make & selectively destroy ECM JOINT CARTILAGE VULNERABILITIES Thin and easily worn away (osteoarthrosis) Relies on very indirect nutrition A few cells look after extensive matrix Has nearby a loose CT (synovium) in which damaging defensive responses occur, e.g., to crystals (gout), virus? (rheumatoid arthritis) Inflammatory synovial cells release damaging enzymes into synovial fluid, or cytokine signals turning on chondrocyte ECM destruction Large ECM molecules (PGs & Collagen) easily cleaved by enzymes into useless shorter pieces CARTILAGE TYPES HYALINE CARTILAGE ELASTIC CARTILAGE Precursor to bony skeleton stays on as Articular cartilage Laryngeal Airway pieces skeleton Tracheal rings like hyaline, but reinforced with elastic fibers a few ‘vocal’ Laryngeal pieces FIBROCARTILAGE joins bones, e.g., vertebrae, & tendons to bone more like dense fibrous tissue Auricle (“ear’) CARTILAGES: Technical names Ears Auricular cartilage elastic Nose Nasal/septal cartilage Airway Laryngeal & tracheal cartilages Ends of ribs Costal cartilages Spine disks Intervertebral disks fibrocartilage Joints Articular cartilages The rest are hyaline, as is most of the embryonic skeleton TYPICAL PIECE* OF CARTILAGE PERICHONDRIUM ( dense irregular CT) Chondrocytes vessels * Fibrocartilage does not occur as discrete pieces CARTILAGE GROWTH PERICHONDRIUM Chondrocytes Chondroblasts Appositional growth by surface cell division & differentiation Interstitial growth by interior cell division & matrix depostion JOINT COMPONENTS SYNOVIUM Joint cartilage absorbs and spreads load Spongy bone with struts/ trabeculae JOINT CAPSULE LIGAMENT Periosteum Fibrous Osteoblastic JOINT CAPSULE & SYNOVIUM SYNOVIUM JOINT SPACE Synovium lines the joint capsule, but it itself has a lining or surface JOINT CAPSULE EASY SLIDING FIRM ELASTIC SUBSTRATE BOUNDARY LUBRICANT FLUID FILM FIRM ELASTIC SUBSTRATE EASY SLIDING: Synovial Joint Articular layer or Disc Attached, polar PHOSPHOLIPID molecules Articular layer WATER + HYALURONAN + PROTEINS Hydrophilic side attaches to cartilage Bond to Hydrophobic side lowers surface energy for NONSTICK surface SYNOVIOCYTE ROLES SYNOVIAL FLUID ‘FIBROBLAST’ synthesizes hyaluronan & glycoproteins ‘MACROPHAGE’ phagocytoses debris in the joint space SUB-INTIMA for inflammatory defensive responses ECM MOLECULAR INTERACTIONS - Pathology 2 Unwanted degradation by bystander inclusion in cytokine signaling pathways of defensive cells IL-1 MF Lymphocytes of inner joint synovium IL-1 Articular chondrocytes Joint cartilage cells also respond to the signal: enzymes enzyme inhibitors proteoglycans = an inappropriate response causing cartilage matrix destruction - ARTHRITIS JOINT PANNUS SYNOVIUM PANNUS is a overgrowth of inflamed synovium onto & eating into the articular cartilage Joint cartilage PTERYGIUM is a similar, but less inflamed growth of conjunctiva onto the eye’s cornea SKELETAL DEVELOPMENT Skeletal piece of hyaline cartilage Grows by internal expansion and from the surface Cell enlargement/hypertrophy Matrix calcification Calcified cartilage can be resorbed like bone, and be attached to bone selective erosion into mineralized cartilage EARLY ENDOCHONDRAL OSSIFICATION perichondrium periosteum Bony collar provides support as mineralized cartilage is eaten away } EPIPHYSIS } DIAPHYSIS/SHAFT primary ossification front LATER ENDOCHONDRAL OSSIFICATION Articular cartilage Growth/epiphyseal plate Secondary ossification centers - + Shaft bone grows by deposition on the outside, with mild resorption on the inside surface, plus osteonal remodelling in the interior Bone would be larger than in the previous view ZONES/LAYERS OF THE GROWTH PLATE }RESTING } PROLIFERATION Expansion } HYPERYTROPHY } Matching erosion Osteoclasts stop the trabeculae from forever extending CALCIFICATION } OSSIFICATION new bone on calcified cartilage Cartilage is replaced by bone. There is no transformation of cartilage into bone WHERE AM I? Online Anatomy Module 1 ORIENTATION You are at the End CELL EPITHELIUM Caution how you exit. BACK on your CARTILAGE browser is needed MUSCLE Unfortunately there is NERVOUS SYSTEM no way that you can directly reach other AXIAL SKELETON topics listed here by APPENDICULAR SKELETON clicking on them. You get there by going back MUSCLES to the Paramedical Anatomy menu EMBRYOLOGY