Skeletal System 1 (Bone Structure)

• Skeletal system primary functions

  • Support - Body, soft tissues, organs
  • Storage of minerals and lipids - Calcium, phosphate, Yellow bone marrow stores lipids
  • Blood cell production - Long bones produce red, white cells and more
  • Protection - Heart, lungs, brain, spinal cord
• Classification of Bones

  • Bone are identified by: Shape - Long, flat, irregular, short, sesamoid
  • Bone markings - Depressions, projections, tunnels
  • Internal tissues - Compact, spongy
• Bone types


  • Thin with parallel surfaces found in the skull, sternum, ribs, and scapula
  • Long and thin found in arms, legs, hands, feet, fingers, and toes
  • Small, irregular bones found between the flat bones of the skull
  • Have complex shapes spinal vertebrae pelvic bones
  • Small and thick ankle, wrist bones
  • Small and flat Develop inside tendons near joints of knees, hands, and feet
• Proximal phalange (middle segment of finger), Scapular (shoulder), Coxal (hip), Femur, Radius are classified as bones
• Proximal phalange is a long bone, Scapular and Coxal are irregular bones, Femur and Radius are long bones
• Bone Markings


  • Depressions or grooves along bone surface
  • Projections where tendons and ligaments attach, at articulations with other bones
  • Tunnels where blood and nerves enter bone
• Bone parts

  • Diaphysis - the shaft, compact bone wall, marrow cavity
  • Epiphysis - wide part at each end, articulation with other bones, spongy bone
  • Metaphysis - where diaphysis and epiphysis meet
• Bone (osseous) tissue contains dense matrix, deposits of calcium salts, bone cells within lacunae organized around blood vessels, canaliculi, 2/3 of bone matrix is calcium phosphate, Ca3(PO4)2, 1/3 of bone matrix is protein fibers (collagen)
• Bone Cells

  • Osteocytes, Osteoblasts, Osteo-progenitor cells (immature), Osteoclasts
• Osteocytes are mature bone cells that maintain the bone matrix, help repair damaged bone, and do not divide
• Osteoblasts are immature bone cells that secrete matrix compounds (osteogenesis)
• Osteoclasts secrete acids and protein-digesting enzymes
• Compact bone contains parallel osteons and concentric lay
• These cells do not divide
• Osteoblasts


  • Immature bone cells that secrete matrix compounds (osteogenesis)
• Osteoclasts


  • Secrete acids and protein-digesting enzymes
• Bone types

  • Compact bone
  • Spongy bone
• Compact bone


  • Contains parallel osteons, concentric layers of osteocytes around central canal
• Spongy bone

  • Contains trabeculae, meshwork of supporting fibre bundles
• Osteon


  • The basic unit of mature compact bone, osteocytes are arranged in concentric lamellae around a central canal containing blood vessels
• Bone cells


  4 separate types (but really 2 with life cycles): osteoprogenitor → osteoblast → osteocyte. Progenitor cells are dividing cells that differentiate into osteoblasts. Osteoblasts build bone and when they have constructed matrix around them, mature into osteocytes. Osteocytes maintain mineral and protein content of surrounding matrix, and are involved in repair of fractures
• Osteoclast


  • These largely dissolve and remove matrix via enzymes, allowing the body to make use of minerals as required
• Actions of Osteoblasts and Osteoclasts


  Usually balanced
• Spongy Bone does not have osteons. The matrix forms an open network of trabeculae. Trabeculae have no blood vessels
• Periosteum


  • Functions: Isolate bone from surrounding tissues, provide a route for circulatory and nervous supply, participate in bone growth and repair
• Endosteum


  • An incomplete cellular layer that lines the marrow cavity, covers trabeculae of spongy bone, and lines central canals. Contains osteoblasts, osteoprogenitor cells, and osteoclasts. Is active in bone growth and repair
• Bone growth


  Continuous remodeling can change the matrix and leave the shape the same. Can change the shape or internal structure of the bone. Involves osteocytes, osteoblasts, and osteoclasts. Osteocytes continuously remove/replace calcium salts. Osteoclasts (remove) and osteoblasts (build) work in balance
• Mineral recycling allows bones to adapt to stress. Heavily stressed bones become thicker and stronger. Markings on bone can indicate the type of stress e.g. fractures, weightlifting. Bone degenerates quickly, up to 1/3 of bone mass can be lost in a few weeks of inactivity. Osteoblasts are attracted to electrical fields created when bone is stressed
• Matrix


  Composed of collagen and non-collagenous organic materials.
• Canaliculi 


  Are small canals running through the bone solid matrix, hosting osteocyte's dendrites, and saturated by an interstitial fluid rich in ions.