1.3 bone & skeleton

Bones

  • Bone = connective tissue made of cells suspended in a matrix   * 65% mineral compound (hydroxyapetite)   * 30% organic material (mostly collagen)
  • organs made up of bone tissue
  • dynamic & respond to changes in their environment.

Layers of bone

 diaphysis = middle (shaft), mostly hollow, houses bone marrow, produces immune cells

  1. Outer - periosteum → coats outside of bone, has blood supply which continues into centre
  2. Mid - cortical (compact) bone
  3. Inner - trabecular (spongey bone)
  4. Medullary cavity - contains bone marrow (immunity)
  5. Epiphyseal plate (growth plate) - filled w/ cartilage, helping juvenile grow via elongation
  6. Bones join at articular cartilage - smooth gliding & cushioning of joints

Bone marrow

  • yellow - adipose tissue
  • red - blood cell production (rbc, wbc & platelets)

Other bone structures

  • Flat bones   * No medullary cavity   * 2 layers of compact bone surrounding either spongy bone or air/space
  • Short bones/irregular bones   * No medullary cavity   * Develop from a single centre of ossification
  • Sesamoid bones   * E.g. patella / fabellae (dog)   * Found near joints   * Ease tendon path & prevent excessive tendon wear   * Increases moment arm of muscle

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Macroscopic architecture

Osteons
  • collection of lamellae
  • structure:   * collagen fibres allow each ‘doughnut’ to hold each other   * collagen fibres run in different directions in neighbouring lamellae   * more resistant to twisting forces, but still allows some form of ‘give’
Surface markings
  • for leverage & muscle attachment
  • Response to strain within bone
  • Articulations with other bones

Bone membranes

 

Periosteum - covers outside of bone

  • 2 layers
  • Protective of underlying tissue
  • Greater osteogenesis than osteolysis
  • Site of sensory nerves, blood & lymphatic vessels
  • highly cellular

\ Endosteum - lines medullary cavity

  • Single layer - thin layer as it only has physiological function (not mechanical)
  • Osteolysis great than osteogenesis (can produce new & remove unwanted bone tissue)

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Blood & nervous supply of bones

  • Well vascularised
  • Arteries enter bone via nutrient foramen in diaphysis
  • Arteries pass through subchondral bone to supply calcified part of cartilage (CARTILAGE ITSELF IS AVASCULAR, but blood supply is v. close)
  • Haversian (ups & down) & volkmann (distal & medial) canals supply cortical bone
  • Trabecular bone supplied via bone marrow

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