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

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

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)

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