connective/supporting tissue bears mechanical stress without distortion -> shock absorption smooth surface -> facilitates movements of joints guides development of bones chondrocytes extracellular matrix (ECM): high concentrations of glucosaminoglycans (GAG) proteoglycans (core protein) hyluronic acid collagen (Type II > I) elastic fibres lacunae physical properties depend on: electrostatic bonds between collagen/elastic fibers and GAGs water bound to negatively charged sulfated GAG chains avascular: nutrients from surrounding connective tissue (perichondrium) by diffusion -> chondrocytes have low metabolic activity no lymphatic vessels or innervation -> low regenerative properties http://marvistavet.evetsites.net/sites/site-5348/images/arthritis/gag.gif
homogeneous, semitransparent articular surfaces of movable joints walls of larger respiratory passages ventral ends of ribs epiphyseal plates of long bones (longitudinal growth) embryonal cartilage later replaced by bone
Extracellular matrix 40% collagen (Type II) binds: hydrated gel of proteoglycans and structural gylocproteins proteoglycans: basophilic aggrecan: cca. 150 GAG side chains of chondroitin sulfate & keratan sulfate chondrocytes bind to ECM via chondronectin the more GAG, the more basophilic (territorial vs. interterritorial matrix)
Cellular components fewer cells than in other types of cartilage at periphery: elongated chondroblasts aligned parallel to surface deeper: round chondrocytes groups of 2-8 originating through mitosis from one chondroblast -> isogenous aggregates through secretion of ECM cells are pushed apart -> separate lacunae dehydration of tissue during histological preparation -> cells shrink and separate from lacunar wall no blood supply -> low metabolic rate: glucose -> anaerobic glycolisis -> lactic acid diffusion helped by compression & decompression can only exist as thin plates
perichondrium: dense connective tissue, collagen Type I + fibroblasts & chondroblasts chondrocytes: active - basophil; inactive: glycogen + lipid droplets chondron (territorium): isogenic group of chondrocytes + territorial matrix lacunae pericellular matrix (capsule): strong basophilia territorial matrix: basophil interterritorial matrix: weak basophilia
zones of articular cartilage: 1. parallel to surface 2. crossing fibres 3. perpendicular to surface 4. calcified pressure applied -> some water is forced out of the cartilage matrix into the synovial fluid pressure released -> water is attracted back into the interstices of the matrix. essential for nutrition of the cartilage and for facilitating the interchange of O2, CO2, and other molecules between the synovial fluid and the articular cartilage.
ECM: collagen Type II + elastic fibres -> greater flexibility than hyalin cartilage staining: resorcin fuchsin, orcein cartilage of ear larynx: epiglottis, cuneiform perichondrium
mixture of hyalin cartilage & dense connective tissue intervertebral discs attachment of ligaments pubic symphysis
chondrocytes singly and aligned in isogenous aggregates separated by fibroblasts and dense collagen Type I. NO perichondrium intervertebral disc anulus fibrosus: fibrocartilage nucleus pulposus: remnant of notochord, gel-like matrix shock-absorbers
Chondrogenesis from embryonic mesenchyme mesenchymal cells round up, retract extensions dividing cells: chondroblast cytoplasm rich in RER (basophilic): collagen synthesis production of ECM separates cells interstitial growth: mitotic division of chondroblasts appositional growth: differentiation of new chondroblasts from perichondrium repair is slow: dense connective tissue from perichondrium
specialized connective tissue provides support for body protects vital organs harbors cavities containing bone marrow for production of blood cells reservoir of calcium, phosphate, ions form a system of levers for transferring force ECM: calcified (bone matrix) cellular components: osteocytes osteoblasts: synthetise organic components of ECM osteoclasts: multinucleated cells resorpting bone
osteocyes: in lacunae between lamellae of bone matrix, with cytoplasmic processes in canaliculi no diffusion of metabolites through calcified matrix -> canaliculi endosteum: surrounds marrow cavity periosteum: external surface, fibrous and cellular layers Matrix dry weight: 65% inorganic, 35% organic organic: 90% collagen Type I. inorganic: hydroxyapatite, Ca2+, Mg2+
differentiate from osteoprogenitors in peri/endosteum differentiate into osteocytes synthetise organic components of matrix (collagen Type I, proteoglycans, glycoproteins) deposit inorganic components of bone located in one layer on surface of bone matrix active: cuboidal/columnar inactive: flat polarized: secretion on side of bone matrix
appositional growth calcification: osteocalcin (polypeptide) binds Ca2+ matrix vesicles (alkaline-phosphatase) attract PO4- ions
differentiate from osteoblasts surrounded by their own secreted materials located in regularly arranged lacunae long dendritic processes in canaliculi radiating from lacunae metabolic exchange through extracellular fluid in canaliculi gap junctions between osteocytes maintain the matrix sclerostin protein sense mechanical stress on bone
large, motile, mononucleated originate from fusion of bone-marrow derived monocytes osteoblast-derived factors induce differentiation located in enzymatically etched depressions: resorption cavities / Howship lacunae ruffled border at attachment zone secretes collagenase, enzymes, H+ receptors for calcitonin (thyroid hormone, lowers blood Ca2+ by inhibiting osteoclast activity) osteoblasts activated by parathyroid hormone (increases blood Ca2+ by stimulating the fusion of osteoclast precursors)
inorganic material: 50% of dry weight calcium hydroxyapatite: hydrated bicarbonate citrate magnesium ions potassium ions sodium ions organic material type I collagen: associates with minerals proteoglycan aggreagtes osteonectin glycoprotein osteocalcin: calcium-binding protein phosphatases in matrix vesicles
compact bone lamellae speciales: in osteon laminae generales externae / internae: parallel to surface of bone laminae intercalares / interstitiales: between l. spec. & l. gen. spongy bone trabeculae
periosteum outer dense connective tissue: blood vessels, collagen bundles, fibroblasts perforating (Sharpey) fibres: collagen fibres penetrating bone matrix, binds periosteum to bone inner cellular layer: osteoblasts, osteoprogenitor mesenchymal cells (can differentiate into osteoblasts) nourishes osteous tissue supplies osteoblasts for appositional growth endosteum covers trabeculae projecting into marrow cavities osteoprogenitor cells, osteoblasts
osteoarthritis aging gradual loss or changed physical properties of hyaline cartilage: loss of proteoglycans -> collagen exposed released fragments trigger secretion of matrix metalloproteinases etc. -> inflammation -> pain https://en.wikipedia.org/wiki/osteoarthritis#/media/file:0910_oateoarthritis_hip_a.png https://en.wikipedia.org/wiki/file:722_feature_osteoprosis_of_spine.jpg osteoporosis in immobilized patients and postmenopausal women bone resorption exceeds bone formation calcium loss from bones and reduced bone mineral density (BMD) RNKL / RNK / OPG (osteoprotegerin) system https://en.wikipedia.org/wiki/file:blausen_0686_osteoporosis_01.png
https://www.youtube.com/watch?v=vwckyf0lqwo
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