Chapter 6 Cartilage and Bone Connective Tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Review Chapter 4 – Tissues connective tissues Skeletal System Components Functions (mostly of bone) • bones • support • protection • cartilage • lever for movement • ligaments • major storage and source of ++ --- • other – minerals: Ca and PO4 as calcium supportive phosphate & calcium carbonate connective – fat in white marrow: lipid-soluble hormones & vitamins tissue • hematopoiesis: blood cell formation & structures maturation in spongy bone spaces Skeletal System • cartilage “semi-rigid” • bone • chondrocytes • osteocytes • avascular – osseous tissue – hyaline cartilage • ~ 2/3 mineral = mostly • basic cartilage structure hydroxylapatite = calcium phosphate + • mostly ground substance calcium carbonate • few & thin fibers • ~ 1/3 collagen fibers – usually not visible • + cells = osteocytes – fibrocartilage • ~ hyaline cartilage + – compact bone collagen fiber bundles • osteons – elastic cartilage – spongy bone • ~ hyaline cartilage + elastic • trabecula(e) fiber bundles cartilage in the skeletal system Figure 6.1 hyaline “glassy” cartilage - translucent perichondrium perichondrium perichondrium fibrocartilage: resilient, shock absorber NO perichondrium blends with surrounding DIFCT elastic cartilage: flexible yes perichondrium --- not shown here Formation Figure 6.2 and Growth of Cartilage chondroblast chondrocyte perichondrium lacuna appositional vs interstitial growth Formation and Growth of Cartilage ORIGIN = mesenchyme: cluster of mesenchymal cells Central cells become chondrocytes; outer rim → perichondrium with chondroblasts appositional growth interstitial growth “appose” – at edge, nearby “between the stuff” • mitosis of stem cells in • mitosis of chondrocytes in lacunae perichondrium • → two chondroblasts per lacuna • adds chondroblasts to periphery • each synthesize and secrete new • → produce matrix, matrix • become chondrocytes in lacunae • new matrix separates the cells, • results: now called chondrocytes – larger piece of cartilage • results: – newest cartilage on outside – larger piece of cartilage edges – newest cartilage on the inside 5 bone shape categories ALL: compact bone on outside & spongy bone in center • long • cuboidal – not so“short” • flat • irregular • odd (also part of other shape group) – sutural = Wormian – sesamoid not all so “short” !!→ Figure 6.3 cells in bone – note effects on bone & on serum (blood) Ca++ stem cells Figure 6.6 cells in bone – note their effects on bone & on serum (blood) Ca++ • Osteoprogenitor cells – stem cells from mesenchyme – found in endosteum and periosteum → either another stem cell or an osteoblast • Osteoblasts – >> bone matrix – differentiates into osteocytes • Osteocytes – in lacunae – maintain the bone matrix – communicate with osteoblasts →deposit more bone matrix • Osteoclasts – large, multinuclear cells <– derived from fused macrophages – in resorption lacunae – dissolve bone = osteolysis → releases Ca++ • Osteoclasts and osteoblasts have opposite effects on bone density & serum Ca++ bone matrix composition • organic and inorganic components – ~ 1/3 organic • cells • collagen fibers • ground substance – ~ 2/3 inorganic • Ca++ salts – Calcium hydroxide – calcium phosphate →bone salt crystals = hydroxyapatite – Ca10(PO4)6(OH)2 ** but actually quite variable *** Table 6.1 Page 153_01 Osteitis deformans imbalance between osteoclast & osteoblast activities Figure 6.5 periosteum & endosteum osteoblasts red marrow fused macrophages Figure 6.8 compact bone tissue: osteons & spongy bone tissue • central (Haversian) canal – carries vessels and nerves in center of osteon • concentric lamellae “lamella” = “layer” – rings of bone around central canal • osteocytes in lacunae between lamellae • canaliculi = channels between lacunae – osteocytes connect & communicate – nutrient & waste exchange < -- > central canal • circumferential lamellae – rings of bone immediately internal to • periosteum • endosteum – entire circumference of the bone • interstitial lamellae Compact Bone – leftover parts of osteons that have Microscopic been partially resorbed Anatomy bone is dynamic – remodeling constantly Click to edit Master title style • osteon (Haversian system) Compact Bone - – basic unit of compact bone – cylindrical Osteons – parallel to the diaphysis • Parallel to compression stress lines • perforating canals – ~ perpendicular to & connect multiple central canals – passageways for blood & lymphatic vessels and nerves • rings of lacunae between lamellae • canaliculi – allow osteocytes to interact What else do you see? Figure 6.9 scanning EM LM: H & E spongy bone NO osteons why not? • immersed in red marrow • no need for central canals • lamellae • lacunae • canaliculi • endosteum • osteoclasts why ? What else do you see? How do the osteocytes survive? Figure 6.7 Figure 6.4 Long Bone • 1 diaphysis – mostly compact bone – marrow cavity • 2 epiphyses – mostly spongy bone • 2 metaphyses Bone Structure – not just long bones • Articular cartilage – Hyaline cartilage – Covers articulating surfaces of any bone participating in a synovial joint • No pericondrium against bone • Endosteum covers – Internal surface – Trabeculae • Periosteum – DIFCT / DRFCT depending on mechanical stress at site – Perforating fibers anchor into compact bone Long Bone Structure • red marrow – found in all spongy bone – hematopoiesis • yellow marrow – in medullary cavity of [large] long bones – adipose tissue – store lipid soluble • hormones • vitamins OSSIFICATION – OSTEOGENESIS ~ 8th week prenatal → entire life ENCHONDRAL O.- INTRAMEMBRANOUS O.- • hyaline cartilage • mesenchyme model • skull flat bones • most bones (most) • (– see exceptions →) • some facial bones • mandible • central clavicle intramembranous ossification • mesenchymal cells form fibrous CT • some differentiate into osteoblasts • → lay down osteoid • → calcification • enclosed cells differentiate into woven bone osteocytes • Note: bone is never exposed – there is ALWAYS a periosteum lamellar bone of DFCT Figure 6.10 enchondral ossification – e.g. long bone Figure 6.11 Stages of Endochondral Ossification • fetal hyaline cartilage model develops • cartilage calcifies due to invasion by blood vessels and increased oxygen • periosteal bone collar forms • primary ossification center forms in the diaphysis • secondary ossification centers form in the epiphyses • bone replaces cartilage, except – articular cartilage – epiphyseal plates • epiphyseal plates ossify and form epiphyseal lines hormonal effects ~ puberty & beyond Page 159_01 15 – 23 years old < 15 years old note extent of epiphyseal fusion Epiphyseal Plate Zones Figure 6.13 “appositional” bone growth – growth in diameter or thickness – requires remodeling – osteoclast activity – osteoblast activity arterial supply to a long bone * all bones * ** Nutrient arteries and veins • supply the diaphysis of long bones • nerves usually accompany these blood vessels into the bone Metaphyseal arteries and veins • supply the junctional area between the diaphysis and the epiphysis Epiphyseal arteries and veins • supply the cells of the Figure 6.14 epiphyseal plate ** Periosteal arteries and veins • supply blood to the external circumferential lamellae • superficial osteons Page 163_01 Bone scans measure metabolic activity • “hot spot” = increased metabolism • “cold spot” = decreased metabolism Homeostasis & Promoting Bone Growth growth, maintenance, and repair depend on: • hormones: regulate osteoblast and osteoclast activity → regulate calcium levels • growth hormone stimulates cartilage growth at epiphyseal plate • thyroid hormone stimulates metabolic rate of osteoblasts • calcitonin and parathyroid hormone have opposite effects on calcium • calcitonin promotes calcium deposit from blood to bone • parathyroid hormone stimulates osteoclasts to resorb bone and increase levels of calcium in the blood • vitamins • vitamin A activates osteoblasts • vitamin C required for collagen synthesis • vitamin D stimulates calcium absorption from GI tract into blood • so that calcium is available for building bone • Exercise • mechanical stress stimulates increase in bone density by increased osteoblast activity • bones of athletes become thicker and stronger as the result of repetitive and stressful exercise • bones lose mass with age, but this can be slowed or reversed with weight-bearing exercise Homeostasis & Promoting Bone Growth Figure 6.15 Bone Fractures Table 6.2 Bone Fractures Figure 6.15 Bone Fractures Figure 6.15 Figure 6.16 Bone Fracture Repair (usually 4-8 weeks if all goes well) Figure 6.17 Bone Markings & Landmarks bone -- ageing during aging, bone changes in two main ways: • loses ability to produce organic matrix (mainly collagen) • loses calcium and other minerals – osteopenia: insufficient ossification – can result in a decrease in bone mass called osteoporosis – increase chances of fractures • Note – the ability to repair & remodel is maintained – though possibly impaired Page 167_01 Osteogenesis –> Osteoporesis - animation.