Skeletal System 5a

• Origin of bone

  1. Protection (armour) , head shields (durability)
  2. osmoregulation, impermeable surface (hangfish isotonic to seawater)
  3. storage, phosphorus is scarce and important in metabolism
  4. sequestering, build up of phosphorus and calcium is detrimental to muscle activity
  5. resistance to acidity, muscle activity can reduce pH of body fluids, lactic acid
  6. electroreception, insulation for electroreceptors
• Origin of bone

  1. first as dermal bone ostracoderm head shield (similar to cosmoid scales)
  2. internal skeleton cartilage first , poorly preserved, ossified later with increased motility
  3. Trabecular bone (dentine - neural crest, bone - mesodermal cells)
• Embryology

  1. mesenchyme: embryonic connective tissue, primarily mesoderm - connective tissue - through neural crest
  2. Gives rise to -
  3. fibroblasts - secretes collagen, tendons, ligamanets, and dermis
  4. scleroblastics - secrete rigid extracellular membrane, bone and cartilage
  5. myoblasts - differentiate into muscle fibers
• Cartilage

  • Chondrocytes
  • collagen and elastin fibers
  • chondroitin sulphate matrix (makes rigid and glassy)
  • produced by chondrocytes found in lacunae
  • no blood supply or enervation, gas exchange and nuriton by diffion (low metabolism)
  • resistance to compression (pressure)
  • not resistant to shear (cracking), tension (pulling)
  • flexible, elastic, light weight and quick to grow (slow to heal, quick to grow
• Hyaline cartilage

  • most common
  • pre forms internal skeleton
  • often replaced by bone in growth
  • remains as adults as (ends of long bones, tracheal rings, parts of skull)
  • smooth appearance
  • irregular fibers
  • glassy appearance
• Fibrocartilage

  • intervertebral discs
  • external structures, (ear pinnae, nose )
  • fibrous appearance, orderly
  • flexible
• Elastic Cartilage

  • springy and flexible
  • ear pinnae, epiglottis
  • fibrous appearance, orderly
  • very flexible
  • get trapped once they are there for life
• Calcified cartilage

  • fibrocartilage with calcium salts
  • heavier and more rigid, resists, deformation
  • grows quickly, without remodeling
  • lamprey and shark, embryonic skeleton
  • Chondrichthyes lost bone
• Bone cells

  • osteoblasts - make bone matrix
  • osteocytes - maintain bone, reside in lacunae surrounded by matrix
  • osteoclasts- remove bone matrix- (constantly being destoryed, so, constantly being replaced)
  • matrix made of collagen, glycoproteins CaPO4
  • typically under continuous remodelling - high metabolism
• Bone tissue

  • Haversian bone made of osteons(tubes on tubes, one has blood supply) (abundant in juveniles)
  • laminar bone - strong AF
  • cancellous bone - spongy bone - ie in scales
• Bone tissue

  • Cellular - >
  • osteocytes present, living tissue
  • non lamellar: disorderly matrix, fast growing, immature
  • lamellar: orderly matrix, slow growing, mature
  • Acellular ->
  • no osteocytes present, non living
  • teleost scales - have none at all
• Bone Density

  • Compact bone ->
  • tends to be lamellar
  • outer margin of long bones, dermal bones of skull
  • Spongey (cancellous) bone->
  • tends to be non lammerlar
  • interior of large bones
  • made of bony trabeculae and marrow
  • lightens skelenton and provides space for blood formation and fat storage
• Bone Formation

  • membrane (intramembranous) bone
  • deposited directly
  • mainly dermal bone (humans lost dermal bone except in skull+ collar bone)
  • dermatocranium some bones of girdles
  • Replacement bone ->
  • preformed in cartilage
  • chondrocranium, axial skeleton
  • long bones of tetrapods
• Long Bones

  • epiphysis: terminal end, rounded, synovial joint
  • metaphysis: widening adjacent to physis - gone in adults
  • diaphysis - main shaft
• Long bones

  1. hyaline cartilage precursor
  2. bone collar around diaphysis
  3. cartilage calcified, chondrocytes die
  4. blood vessels invade
  5. onset of ossification
  6. diaphysis lengthened by proliferating chondrocytes that become ossified
  7. secondary center of ossification in epiphysis
  8. loss of physis
• Labelled skeletal head

  
• Skeleton

  • dermal skeleton ->
  • mainly from dermis, not preformed in cartilage (direct ossificaton)
  • bony scales, teeth, dermal bones
  • endoskeleton ->
  • usually performed by cartilage
  • visceral: branchial or pharyngeal skeleton
  • somatic: somites
  • axial: notochord, vertebral column+ ribs, skull
  • appendicular: pectoral and pelvic girdle and associated limbs+fins
• Axial: Cranial skeleton

  1. dermatocranium - skull and teeth (dermal bone) PINK
  2. splanchnocranium - jaws and pharyngeal YELLOW
  3. chondrocranium - neurocranium and brain box BLUE

  
• Axial: Cranial Skeleton

  1. Dermatocranium - teeth only in shark (no skeleton surronding head of shark)
  2. splanchnocranium - jaws and pharyngeal
  3. neurocranium and brainbox

  
• Skeletal connections

  • joints may be synovial or synarthrosis
  • ligaments connect bone to bone
  • tendons connect muscle to bone