Bones

• Bones are alive and dynamic
• You get a whole new skeleton every 7 to 10 years
• Bones

  Store calcium, phosphate, and other minerals<|>Crucial to hematopoiesis<|>Help maintain homeostasis
• Bone marrow generates a trillion blood cells a day
• An average human body contains 206 bones
• Bone groups

  • Axial
  • Appendicular
• Axial bones


  Found along the body’s vertical axis
• Appendicular bones


  Bones that make up limbs and attach to the axial skeleton
• Bone shapes

  • Long
  • Short
  • Flat
  • Irregular
• Long bones


  Limb bones longer than they are wide
• Short bones


  Cube-shaped bones like talus and cuboid
• Flat bones


  Thinner bones like sternum and scapulae
• Irregular bones


  Weirdly-shaped bones like vertebrae and pelvis
• All bones have a similar internal structure

  Dense compact bone around spongy bone
• Spongy bone tissue


  Made up of trabeculae that help resist stress
• Bone marrow


  Comes in two colors: red and yellow
• Red marrow


  Makes blood cells
• Yellow marrow


  Stores energy as fat
• Bone can look rock-solid but is actually intricate
• Osteons


  Basic structural units of bone
• Osteons


  Cylindrical, weight-bearing structures that run parallel to the bone’s axis
• Lamellae


  Tubes inside of tubes in osteons
• Osteocytes


  Mature bone cells that monitor and maintain bone matrix
• Osteoblasts


  Bone-building cells
• Osteoclasts


  Bone-breaking cells
• Bone remodeling

  1. Initiated by osteocytes

  2. Direct osteoclasts to damage site

  3. Osteoclasts resorb old bone

  4. Osteoblasts rebuild bone
• Osteocytes sense stress and strain
• Osteoclasts increase their rate of bone resorption in low gravity
• Osteoblasts dial back on bone formation in low gravity
• Exercising stimulates bone remodeling and strength
• In addition to bones, there’s cartilage and fibrous connective tissue that allows them to work together.
• Joints are the meeting places between two or more bones.
• You actually have more joints in your body than you have bones.
• Body movements happen when muscles contract across joints, moving one bone toward another.
• Axial skeleton


  Includes all 80 midline bones that form your skull, vertebral column, and thoracic cage.
• Appendicular skeleton


  Includes your upper and lower limb appendages and pectoral and pelvic girdles.
• Parts of the axial skeleton

  • Skull
  • Vertebral column
  • Thoracic cage
• Parts of the appendicular skeleton


  • Upper limb appendages
  • Lower limb appendages
  • Pectoral girdle
  • Pelvic girdle
• The skull’s eight cranial and fourteen facial bones form your body’s most complex bony structure.
• The 33 irregular bones in your vertebral column start with your atlas vertebra.