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