Skeletal System Powerpoint

• Parts of the skeletal system

  • Bones (skeleton)
  • Joints
  • Cartilages
  • Ligaments

  
• Two subdivisions of the skeleton

  • Axial skeleton
  • Appendicular skeleton

  
• Functions of the bones

  • Support the body
  • Protection of soft organs
  • Allow movement via attached muscles
  • Store minerals and fats
  • Blood cell formation (hematopoiesis)

  
• Compact bone


  Dense, smooth, and homogeneous

  
• Spongy bone


  Small needlelike pieces of bone with many open spaces
• Classification of bones based on shape

  • Long
  • Flat
  • Short
  • Irregular

  
• Long bones


  • Typically longer than they are wide
  • Shaft with enlarged ends
  • Contain mostly compact bone; spongy bone at ends

  
• Flat bones


  • Thin, flattened, and usually curved
  • Two thin layers of compact bone sandwich a layer of spongy bone between them

  
• Short bones


  • Generally cube-shaped
  • Contain mostly spongy bone with an outer layer of compact bone

  
• Irregular bones


  • Irregular shape
  • Mainly spongy bone with an outer layer of compact bone

  
• Diaphysis


  Shaft of a long bone, composed of compact bone

  
• Periosteum


  Outside covering of the diaphysis, a fibrous connective tissue membrane
• Epiphysis


  Ends of a long bone, composed mostly of spongy bone enclosed by thin layer of compact bone

  
• Articular cartilage


  Covers the external surface of the epiphyses, made of hyaline cartilage to decrease friction at joint surfaces
• Epiphyseal line


  Remnant of the epiphyseal plate in adult bones

  
• Epiphyseal plate


  Flat plate of hyaline cartilage seen in young, growing bone that causes lengthwise growth

  
• Endosteum


  Lines the inner surface of the shaft, made of connective tissue
• Medullary cavity


  Cavity inside the shaft, contains yellow marrow (mostly fat) in adults
• Categories of bone markings

  • Projections or processes
  • Depressions or cavities

  
• Trabeculae


  Small, needlelike pieces of bone that make up spongy bone

  
• Osteocytes


  Mature bone cells situated in bone matrix
• Lacunae


  Cavities in bone matrix that house osteocytes
• Lamellae


  Concentric circles of lacunae situated around the central (Haversian) canal
• Central (Haversian) canal


  Opening in the center of an osteon (Haversian system) that carries blood vessels and nerves
• Osteon (Haversian system)


  A unit of bone containing central canal and matrix rings, the structural and functional unit of compact bone

  
• Canaliculi


  Tiny canals that radiate from the central canal to lacunae, forming a transport system connecting all bone cells to a nutrient supply
• Perforating (Volkmann's) canal


  Canal perpendicular to the central canal that carries blood vessels and nerves
• Bone is relatively lightweight and resists tension and other forces
• Organic parts (collagen fibers) make bone flexible and have great tensile strength (stretch without breaking)
• Calcium salts deposited in the bone make bone hard (resists compression)
• Ossification


  1. Process of bone formation

  2. Occurs on hyaline cartilage models or fibrous membranes
• Two major phases of ossification in long bones

  1. Osteoblasts cover hyaline cartilage model with bone matrix

  2. Enclosed cartilage is covered by bone, cartilage is digested away, opening up a medullary cavity
• Intramembranous ossification


  Forms flat bones as in skull

  
• Endochondral ossification


  Forms long bones

  
• Intramembranous ossification


  1. Development of ossification center

  2. Calcification

  3. Formation of bone trabeculae

  4. Development of periosteum
• Mesenchymal cells differentiate into osteoprogenitor cells


  1. Osteoprogenitor cells develop into osteoblasts

  2. Osteoblasts appear in clusters called ossification center

  3. Osteoblasts secrete osteoid (collagen fibers + protein)

  4. Osteoid forms the extracellular bone matrix

  5. Osteoblasts trapped in the bone matrix become osteocytes
• Calcification


  1. Calcium and mineral salts are deposited in the extracellular matrix

  2. Extracellular matrix becomes hard or calcifies
• Formation of bone trabeculae

  1. Extracellular matrix develops into bone trabeculae

  2. Trabeculae fuse to form a spongy bone

  3. Spongy bone around blood vessels differentiates into red bone marrow
• Development of periosteum


  1. Mesenchyme cells at the periphery develop into periosteum

  2. Compact bone replaces the surface layer of spongy bone

  3. Spongy bone remains in the center

  4. Newly formed bone is remodeled as it transforms into adult size and shape

  
• Endochondral Ossification (Within Cartilage)

  1. Mesenchymal cells develop into chondroblasts

  2. Chondroblasts secrete extracellular matrix of hyaline cartilage

  3. Perichondrium develops around the cartilage model

  4. Chondroblasts trapped in the matrix become chondrocytes

  5. Chondrocyte division makes the bone grow in length (interstitial growth)

  6. Cartilage growth in thickness by deposition of chondroblasts is appositional growth

  7. Bone tissue replaces most of the cartilage in the diaphysis region

  8. Osteoclasts break down bone to form the medullary cavity

  9. Secondary ossification centers develop in the epiphysis

  10. Hyaline cartilage remains at epiphyseal plate and joint surface as articular cartilage