chapter 8

• Bone


  Hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body
• Cartilage


  Semi-rigid form of connective tissue that provides flexibility and smooth surfaces for movement
• Skeletal system


  Body system composed of bones and cartilage
• Functions of the skeletal system

  • Supports the body
  • Facilitates movement
  • Protects internal organs
  • Produces blood cells
  • Stores and releases minerals and fat
• Bones


  • Act as levers when muscles span a joint and contract
  • Serve as points of attachment for muscles
• Joints

  • Serve as fulcrums for bone movement
• Unless a muscle spans a joint and contracts, a bone is not going to move
• Bones protect internal organs from injury by covering or surrounding them
• Bones protecting organs


  • Ribs protect lungs and heart
  • Vertebral column protects spinal cord
  • Cranium protects brain
• Orthopaedist


  Doctor who specializes in diagnosing and treating disorders and injuries related to the musculoskeletal system
• Orthopaedists can treat bone and joint injuries, as well as other bone conditions including curvature of the spine
• Bone matrix


  Acts as a reservoir for minerals like calcium and phosphorus
• Yellow marrow

  Contains adipose tissue that can serve as a source of energy
• Red marrow

  Where hematopoiesis (blood cell production) takes place
• Diaphysis


  Tubular shaft that runs between the proximal and distal ends of a long bone
• Medullary cavity


  Hollow region in the diaphysis filled with yellow marrow
• Epiphysis


  Wider section at each end of a long bone, filled with spongy bone and red marrow
• Metaphysis


  Narrow area between the diaphysis and epiphysis that contains the epiphyseal plate (growth plate)
• Endosteum


  Delicate membranous lining of the medullary cavity where bone growth, repair, and remodeling occur
• Periosteum


  Fibrous membrane covering the outer surface of bone, containing blood vessels, nerves, and lymphatic vessels that nourish compact bone
• Articular cartilage

  Thin layer of cartilage covering the epiphyses where they meet other bones, reducing friction and acting as a shock absorber
• Bone markings


  • Articulations (where two bones meet)
  • Projections (raised markings for tendon/ligament attachment)
  • Holes (for blood vessels and nerves to enter bone)
• Hydroxyapatite


  Crystals formed from calcium phosphate and calcium carbonate that give bones their hardness and strength
• Bone cells

  • Osteoblasts (form new bone)
  • Osteocytes (maintain mature bone)
  • Osteogenic cells (develop into osteoblasts)
  • Osteoclasts (break down old bone)
• Osteoblasts and osteocytes are incapable of mitosis, so they are replenished by osteogenic cells which have high mitotic activity
• Osteoclasts originate from monocytes and macrophages, not from osteogenic cells
• The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone
• Osteogenic cells


  Develop into osteoblasts
• Osteoblasts


  Responsible for bone formation
• Osteocytes


  Maintain mineral concentration of bone matrix
• Osteoclasts


  Responsible for bone resorption
• Compact bone


  • Dense and strong to withstand compressive forces
  • Found under the periosteum and in the diaphyses of long bones
• Spongy (cancellous) bone


  • Has open spaces and supports shifts in weight distribution
  • Contains osteocytes in a lattice-like network of matrix spikes called trabeculae
• Paget's disease is a disorder of the bone remodeling process that begins with overactive osteoclasts, leading to more bone being resorbed than laid down
• Paget's disease can cause pain, bone fractures, and bone deformities, and commonly affects the bones of the pelvis, skull, spine, and legs
• The cause of overactive osteoclasts in Paget's disease is unknown, but hereditary factors seem to play a role
• Diagnosis of Paget's disease

  1. Imaging studies (X-rays, bone scans)

  2. Lab tests (elevated alkaline phosphatase)
• Bisphosphonates


  Drugs that decrease the activity of osteoclasts, used to treat Paget's disease
• Blood vessels and nerves enter the bone through the nutrient foramen
• Types of body movements

  • Flexion
  • Extension
  • Abduction
  • Adduction
  • Circumduction
  • Rotation