SKELETAL

• Functions of Bone and the Skeletal System

  • Support
  • Assistance in Movement
  • Protection
  • Mineral Homeostasis (Storage and Release)
  • Blood Cell Production
  • Triglyceride Storage

  
• Skeletal System: Bone Tissue


  • Structural framework for the body by supporting soft tissues and providing attachment points for the tendons of most skeletal muscles
  • Protects the most important internal organs from injury
  • Skeletal muscles attach to bones and when they contract, they pull on bones to produce movement
  • Stores several minerals, especially calcium and phosphorus, which contribute to the strength of bone
  • Stores about 99% of the body's calcium and releases minerals into the blood to maintain critical mineral balances
  • Contains red bone marrow that produces red blood cells, white blood cells, and platelets
  • Contains yellow bone marrow that stores triglycerides as a potential chemical energy reserve

  
• Long bone


  One that has greater length than width

  
• Parts of a long bone

  • Diaphysis
  • Epiphysis
  • Metaphysis
  • Articular cartilage
  • Periosteum

  
• Extracellular matrix of bone

  About 15% water, 30% collagen fibers, and 55% crystallized mineral salts

  
• Hydroxyapatite


  Ca10(PO4)6(OH)2, the most abundant mineral salt in bone
• Calcification


  The process of mineral salts being deposited in the framework formed by the collagen fibers of the extracellular matrix, causing the tissue to harden
• Bone


  • Hardness depends on the crystallized inorganic mineral salts, flexibility depends on its collagen fibers
  • Collagen fibers and other organic molecules provide tensile strength
• Osteoprogenitor cells


  Unspecialized bone stem cells derived from mesenchyme, the only bone cells to undergo cell division

  
• Osteoblasts


  Bone-building cells that synthesize and secrete collagen fibers and other organic components needed to build the extracellular matrix of bone tissue, and initiate calcification

  
• Osteocytes


  Mature bone cells that maintain the daily metabolism of bone tissue

  
• Osteoclasts


  Cells derived from the fusion of monocytes that break down the protein and mineral components of the underlying extracellular bone matrix through resorption

  
• Bone is not completely solid but has many small spaces between its cells and extracellular matrix components

  
• Compact bone


  • Contains few spaces, is the strongest form of bone tissue, found beneath the periosteum and makes up the bulk of the diaphyses of long bones, provides protection, support, and resists stresses

  
• Parts of a compact bone

  • Osteons (Haversian systems)
  • Concentric lamellae
  • Lacunae
  • Canaliculi
  • Interstitial lamellae
  • Perforating canals
  • Circumferential lamellae

  
• Spongy bone


  • Arranged in an irregular pattern of thin columns called trabeculae, with spaces between the trabeculae filled with red or yellow bone marrow, lighter in weight to allow for more ready movement

  
• Arteries present in a long bone

  • Periosteal arteries
  • Nutrient artery
  • Metaphyseal arteries
  • Epiphyseal arteries
• Hemopoiesis


  Blood cell production
• Bone


  • Periosteal arteries
  • Nutrient artery
  • Metaphyseal arteries
  • Epiphyseal arteries
• Bone


  • Nutrient veins
  • Epiphyseal veins
  • Metaphyseal veins
  • Periosteal veins
• Nerves


  • Accompany the blood vessels that supply bones
  • Periosteum is rich in sensory nerves, some of which carry pain sensations
• Ossification


  1. Initial formation of bones in an embryo and fetus

  2. Growth of bones during infancy, childhood, and adolescence

  3. Remodeling of bone

  4. Repair of fractures

  
• Intramembranous ossification


  Bone forms directly within mesenchyme, which is arranged in sheetlike layers that resemble membranes

  
• Endochondral ossification


  Replacement of cartilage by bone, bone forms within hyaline cartilage that develops from mesenchyme

  
• Growth in length


  1. Zone of resting cartilage

  2. Zone of proliferating cartilage

  3. Zone of hypertrophic cartilage

  4. Zone of calcified cartilage
• Appositional growth


  Bone can grow in thickness (diameter) only by appositional growth

  
• Bone remodeling


  1. Bone resorption

  2. Bone deposition

  
• Factors affecting bone growth and bone remodeling

  • Minerals
  • Vitamins
  • Hormones
• Fracture


  • Open (compound)
  • Comminuted
  • Greenstick
  • Impacted
  • Pott
  • Colles
• Repair of a bone fracture

  1. Reactive phase

  2. Reparative phase - fibrocartilagenous callus formation

  3. Reparative phase - bony callus formation

  4. Bone remodeling phase

  
• Calcium


  Bone is the body's major calcium reservoir, storing 99% of total body calcium
• Hormones regulating blood calcium level

  • Parathyroid hormone (PTH)
  • Calcitriol
  • Calcitonin (CT)
• Exercise and mechanical stress affect bone tissue
• Aging affects bone tissue
• Bones are the hardest part of our body and serve as support structures, protect vital organs, store minerals such as calcium and phosphorus, produce blood cells, and allow movement through muscle attachment.
• Cartilage is a flexible connective tissue that covers bone ends at joints and provides cushioning between them.
• Cartilages are flexible connective tissues that cover the ends of bones at joints to prevent friction during movement.
• A pivot joint allows for rotation around an axis, such as the joint between the first and second vertebrae of the neck.