Cartilage and Bone PDF

Cartilage Hainza “Cartilage and Bone” CARTILAGE Remember the four basic types of tissue… Epithelium Connective tissue Connective tissue proper Cartilage Bone Blood Muscle tissue Nervous tissue Definition Specialized form of connective tiss...

Cartilage Hainza “Cartilage and Bone” CARTILAGE Remember the four basic types of tissue… Epithelium Connective tissue Connective tissue proper Cartilage Bone Blood Muscle tissue Nervous tissue Definition Specialized form of connective tissue Firm consistency of the extracellular matrix Allows tissue to bear mechanical stress without permanent distortion It supports soft tissues shock absorber because of its resilience  Important in movable joints because of smoothness and its lubricated surface to provide sliding movements. Guides development and growth of long bones Features Extracellular matrix has high concentrations of Glucosaminoglycans (GAGs) & proteoglycans interacts with collagen and elastics fibers Variations in the matrix components and cells produces 3 types of cartilage adapted to local biomechanical needs Hyaline, elastic and fibrocartilage  Chondrocytes produce and maintains extracellular matrix components Cells are found in matrix cavities called lacunae Collagen , hyaluronic acid, proteoglycans and glycoproteins are found in all types of cartilage  Hyaline cartilage is the commonest type and contains collagen type II Elastic cartilage has elastin making it pliability and distensibility Fibrocartilage contains a dense network of coarse type I collagen fibers. Is found in regions subjected to pulling.  Avascular, diffusion from perichondrium, synovial fluid in areas lacking perichondrium. Perichondrium is a dense connective sheath surrounding cartilage. Chondrocytes low metabolic activity No lymphatics and nerves in cartilage but found in the perichondrium.  Firm matrix depends on interaction of collagen and GAGs Binding of water Hyaline Cartilage Most common Fresh cartilage is homogenous, bluish-white and translucent flexible and resilient Sites; embryo making up the skeleton Cartilage Embryo More prevalent than in adult Skeleton initially mostly cartilage Bone replaces cartilage in fetal and childhood periods  In adults: articular surfaces, respiratory tract, costal cartilages, epiphyseal plates Matrix; collagen type II, chondrotin sulfates, keratan sulfate Structural glycoprotein chondronectin Location of hyaline cartilage in adults Nose “Articular” – covering the ends of most bones and movable joints “Costal” – connecting ribs to sternum Trachea, Larynx - voice box  Histology collagen is indiscernible High water content so it is a shocker absorber Territorial/capsular matrix poor in collagen  All hyaline cartilage is covered by Perichondrium except in articular cartilage of joints. Perichondrium is important for growth and mentainance of cartilage. Chondrocytes Isogenous cells Growth hormone, Somatotropin regulates hyaline cartilage growth.  Growth: interstitial and appositional Degenerative changes Regeneration Elastic Cartilage Similar to hyaline but abundant elastic fibers in addition to the collagen type II fibers Yellowish in colour Perichondrium similar to that hyaline is present. No degeneration  Sites: Auricle of ear, Auditory canal, Epiglottis, external auditory canals, cuneiform cartilage in the larynx. Fibrocartilage Intermediate between dense connective tissue and hyaline cartilage Sites: Intervertebral disks, attachment of tendons, ligaments, Pubic symphysis Articular discs such as meniscus in knee joint Always associated with dense connective tissue  Chondrocytes occur singly aligned in isogenous groups produce matrix containing collagen type II fibers. Has no distinct perichondrium.  Types of cartilage: 3 1. Hyaline cartilage: flexible and resilient Chondrocytes appear spherical Lacuna – cavity in matrix holding chondrocyte Collagen the only fiber 2. Elastic cartilage: highly bendable Matrix with elastic as well as collagen fibers Epiglottis, larynx and outer ear 3. Fibrocartilage: resists compression and tension Rows of thick collagen fibers alternating with rows of chondrocytes (in matrix) Knee menisci and annunulus fibrosis of intervertebral discs Hyaline Cartilage Elastic Cartilage Fibrocartilage Growth of cartilage Appositional “Growth from outside” Chrondroblasts in perichondrium (external covering of cartilage) secrete matrix Interstitial “Growth from within” Chondrocytes within divide and secrete new matrix Cartilage stops growing in late teens (chrondrocytes stop dividing) Regenerates poorly in adults Now about bones…like other connective tissue: cells separated by extracellular matrix with collagen but also mineral crystals Bone Bones Functions Support Movement: muscles attach by tendons and use bones as levers to move body Protection Skull – brain Vertebrae – spinal cord Rib cage – thoracic organs Mineral storage Calcium and phosphate Released as ions into blood as needed Blood cell formation and energy storage Bone marrow: red makes blood, yellow stores fat  Is a specialized connective tissue composed of cells and a predominantly collagenous extracellular matrix (type I collagen) called osteoid which becomes mineralised by the deposition of calcium hydroxyapatite. Cells of bones Osteoblasts: synthesise osteoid and mediate its mineralization, are found on the bone surfaces. Osteocytes: inactive osteoblasts trapped within formed bone in cavities known as the lacunae between bone matrix layers (lamellae), with cytoplasmic extention into small canaliculi between lamellae. Osteoclasts: phagocytic multinucleated cells which erode bone and are important in resorption, remodeling and refashioning of bone.Are found in depressions or cavities known as howship lacunae.  Osteoclasts activity is controlled by hormones and signalling factors. They respond to parathyroid hormone and calcitonin Parathyroid hormone stimulates osteoclstic resorption and release of calcium ions from the bone Calcitonin inhibits osteoclastic activity. Applied Anatomy: Osteopetrosis- defective osteoclasts resulting in heavy bones.  Both the internal and external surfaces of bone are lined by connective tissue layers endosteum and periosteum respectively. Both containing osteogenic cells. Extracellular matrix comprises of collagen type I, proteoglycans and several glycoproteins as the organic components, and inorganic components containing calcium hydroxyapatite, phospate, bicarbonate, citrate, magnesium, potasium and sodium ions.  The ions of hydroxyapatite are hydrated, thus the water facilitates the exchange of ions between the mineral and body fluids. Association of minerals with collagen fibers during calcification gives bone its hardness and resitance.  Classification of bones by shape Long bones Short bones Flat bones Irregular bones Pneumatized bones Sesamoid bones (Short bones include sesmoid bones)  Gross anatomy of bones Compact bone (cortical) Spongy (cancellous or medullary or trabecular) bone The expanded ends are called the epiphysis The shaft is known as the diaphysis At the junction of the diaphysis and epihysis in long bones is the epiphyseal or growth plate (occupied with hyaline cartilage during the growign stage of life) Blood vessels Medullary cavity Membranes Periosteum Endosteum  Flat bones Spongy bone is called diploe when its in flat bones Have bone marrow but no marrow cavity Long bones Tubular diaphysis or shaft Epiphyses at the ends: covered with “articular” (=joint) cartilage Epiphyseal line in adults Kids: epiphyseal growth plate (disc of hyaline cartilage that grows to lengthen the bone) Blood vessels Nutrient arteries and veins through nutrient foramen Periosteum Connective tissue membrane Covers entire outer surface of bone except at epiphyses Two sublayers 1. Outer fibrous layer of dense irregular connective tissue 2. Inner (deep) cellular osteogenic layer on the compact bone containing osteoprogenitor cells (stem cells that give rise to osteoblasts) Osteoblasts: bone depositing cells Also osteoclasts: bone destroying cells (from the white blood cell line) Secured to bone by perforating fibers (Sharpey’s fibers) Endosteum Covers the internal bone surfaces Is also osteogenic Bone markings reflect the stresses  Bone markings Projections that are the attachments sites for muscles and ligaments Surfaces that form joints Depressions and openings Learn them using: Marieb lab book p 101, Table 8.1, Bone Markings or Martini p 128, Table 5.1, Common Bone Marking Terminology (next slide) Martini p 128, Table 5.1, Common Bone Marking Terminology (for figure see next slide)  Compact bone Represents about 80% of the total bone mass Osteons: pillars Lamellae: concentric tubes Haversian canals Osteocytes  Isolated osteon: Nutrients diffuse from vessels in central canal Alternating direction of collagen fibers increases resistance to twisting forces Spongy bone Represents about 20% of the total bone mass. Layers of lamellae and osteocytes Seem to align along stress lines  Short bones i.e. wrist and ankle bones have a core of spongy bone surrounded completely by compact bone Flat bones have 2 layers of compact bone called plates separated by a thick layer of spongy bone called diploe. Microscopy shows 2 types of organisation Lamellar bone: composed of regular parallel bands of collagen arranged in sheets. Found in healthy adult bones Woven bone: immature form with randomly arranged collagin fibers in osteoid. Produced when osteoid is produced rapidly e.g. in fetal bone development and in bone pathologies and healing of bone in adults. Woven bone is remodelled to lamellar bone. Chemical composition of bones Cells, matrix of collagen fibers and ground substance (organic: 35%) Contribute to the flexibility and tensile strength Mineral crystals (inorganic: 65%) Primarily calcium phosphate Lie in and around the collagen fibrils in extracellular matrix Contribute to bone hardness Small amount of water Bone development Osteogenesis: “formation of bone” From osteoblasts Bone tissue first appears in week 8 (embryo) Ossification: “to turn into bone” Intramembranous ossification (also called “dermal” since occurs deep in dermis): forms directly from mesenchyme (not modeled first in cartilage) Most skull bones except a few at base Clavicles (collar bones) Sesamoid bones (like the patella) Endochondral ossification: modeled in hyaline cartilage then replaced by bone tissue All the rest of the bones Remember the three germ tissues… 1. Ectoderm - epithelial 2. Endoderm - epithelial 3. Mesoderm is a mesenchyme tissue  Mesenchyme cells are star shaped and do not attach to one another, therefore migrate freely  From the last slide: Intramembranous ossification: forms directly from mesenchyme (not modeled first in cartilage) Most skull bones except a few at base Clavicles (collar bones) Sesmoid bones (like the patella) Intramembranous ossification (osteoid is the organic part) Endochondral ossification Modeled in hyaline cartilage, called cartilage model Gradually replaced by bone: begins late in second month of development Perichondrium is invaded by vessels and becomes periosteum Osteoblasts in periosteum lay down collar of bone around diaphysis Calcification in center of diaphysis Primary ossification centers Secondary ossification in epiphyses Epiphyseal growth plates close at end of adolescence Diaphysis and epiphysis fuse No more bone lengthening See next slide Endochondral ossification Stages 1-3 during fetal week 9 through 9th month Stage 5 is process Stage 4 is just of long bone growth before birth during childhood & adolescence Organization of cartilage within the epiphyseal plate of a growing long bone Epiphyseal growth plates in child, left, and lines in adult, right (see arrows) Factors regulating bone growth Vitamin D: increases calcium from gut Parathyroid hormone (PTH): increases blood calcium (some of this comes out of bone) Calcitonin: decreases blood calcium (opposes PTH) Growth hormone & thyroid hormone: modulate bone growth Sex hormones: growth spurt at adolescense and closure of epiphyses Bone remodeling Osteoclasts Bone resorption Osteoblasts Bone deposition Triggers Hormonal: parathyroid hormone Mechanical stress Osteocytes are transformed osteoblasts Terms (examples) chondro refers to cartilage chondrocyte endochondral perichondrium osteo refers to bone osteogenesis osteocyte periostium blast refers to precursor cell or one that produces something osteoblast cyte refers to cell osteocyte Repair of bone fractures (breaks) Simple and compound fractures Closed and open reduction Disorders of cartilage and bone Defective collagen Numerous genetic disorders eg. Osteogenesis imperfecta (brittle bones) – AD (autosomal dominant) eg. Ehlers-Danlos (rubber man) Defective endochondral ossification eg. Achondroplasia (short –limb dwarfism) - AD Inadequate calcification (requires calcium and vitamin D) Osteomalacia (soft bones) in adults Rickets in children Note: “AD” here means autosomal dominant inheritance (continued) Pagets disease – excessive turnover, abnormal bone Osteosarcoma – bone cancer, affecting children primarily Osteoporosis – usually age related, esp. females Low bone mass and increased fractures Resorption outpaces bone deposition Normal bone Osteoporotic bone