Chapter 6

• In bones, the young bone has a layer of cartilage at the end called the epiphysis, where bone growth occurs, while the adult bone lacks this cartilage as it has stopped growing

  
• A long bone consists of a hard outer layer called compact bone, surrounding a softer inner layer called the medullary cavity, which contains red bone marrow responsible for producing blood cells

  
• Collagen fibers in bones provide strength and flexibility, while the mineral matrix provides hardness and rigidity
• Bone cells maintain bone structure and regulate growth and repair processes
• Hyaline cartilage is intimately associated with bone, often involved in bone growth and repair processes
• Cartilage growth involves chondroblasts adding new cartilage in appositional growth and chondrocytes dividing and adding more matrix in interstitial growth
• Bone matrix is about 35% organic and 65% inorganic material, with organic material primarily consisting of collagen and proteoglycans, and inorganic material primarily of calcium phosphate crystal called hydroxyapatite
• Three types of bone cells: osteoblasts are bone-building cells, osteocytes maintain bone structure, and osteoclasts are bone-destroying cells responsible for bone reabsorption
• The functional unit of compact bone is an osteon, or haversian system, with concentric lamellae surrounding the central canal and circumferential lamellae forming the outer surfaces
• Perforating canals (Volkmann canals) deliver blood to the central canals of the osteons in compact bone
• Flat bones have an interior framework of spongy bone between two layers of compact bone, while short and irregular bones have compact bone surfaces surrounding a spongy bone center filled with marrow
• In bones, the epiphysis is a layer of cartilage at the end of a young bone where growth occurs, while adult bones lack this cartilage layer as they have stopped growing

  
• A long bone's structure includes:

  • Compact bone (hard outer layer)
  • Medullary cavity (softer inner layer containing red bone marrow for blood cell production)
  • Collagen fibers providing strength and flexibility, embedded in a mineral matrix for hardness
  • Bone cells maintain bone structure and regulate growth and repair

  
• Gross anatomy of a long bone:

  • Long bones have a diaphysis (shaft) sandwiched between two layers of compact bone
  • Short and irregular bones have a composition similar to the epiphyses of long bones, with compact bone surfaces surrounding a spongy bone center filled with marrow
  • Sinuses in flat and irregular bones of the skull are air-filled spaces lined by mucous membranes

  
• Bone development:

  • Intramembranous ossification starts within embryonic connective tissue membranes
  • Endochondral ossification starts with a cartilage model
• Bone growth:

  • Long bones grow in length at the epiphyseal plate by creating new cartilage
  • Bones increase in width through appositional bone growth beneath the periosteum
• Factors affecting bone growth:

  • Nutrition: Vitamin D aids calcium absorption, Vitamin C is needed for collagen synthesis
  • Hormones: Growth hormone stimulates bone growth
• Bone remodeling:

  • Converts woven bone to lamellar bone
  • Allows bone to change shape, adjust to stress, repair itself, and regulate body calcium levels
• Bone fracture classification:

  • Mechanism of fracture: traumatic, pathologic, or periprosthetic
  • Soft-tissue damage: closed (stable) or open (compound)
  • Displaced vs. nondisplaced fractures, fracture patterns, number and arrangement of bone fragments
• Bone repair:

  • Steps: hematoma formation, callus formation, callus ossification, bone remodeling
• Osteoporosis:

  • Loss of bone matrix leading to porous and weakened bones prone to fracture
  • Causes include decreased reproductive hormone production, inadequate dietary intake of calcium, and lack of exercise