Skeletal system

• Skeletal System


  • Describe the six functions of the skeletal system
  • Classification of bones on the basis of their shape and location
  • Describe the parts of a long bone and the features of bone tissue
  • Explain the importance of bone formation and bone growth during a person's lifetime
  • Describe how exercise and mechanical stress affect bone tissue
  • Name the cranial and facial bones and indicate their locations and major structural features
  • Identify the regions and normal curves of the vertebral column and describe its structural and functional features
  • Identify the bones of the thorax and their principal markings
  • The bones of the upper and lower limbs and their principal markings
  • The bones of the pelvis and their principal markings
  • Differences between female and male skeletons
  • Effects of aging on the skeletal system
  • Disorders of the skeletal system
• Skeletal System


  The entirety of the bones and their cartilage
• Bone


  An organ composed of different tissues: bone (osseous) tissue, dense connective tissue, epithelium, adipose tissue, nervous tissue
• Functions of Bone and the Skeletal System

  • Support
  • Protection
  • Assistance in movement
  • Mineral homeostasis
  • Blood cell production
  • Triglyceride storage
• Long Bones


  • Greater length than width
  • A shaft
  • Variable number of ends
  • Curved for strength
  • Examples: femur, tibia, fibula, humerus, ulna, radius, phalanges
• Short Bones


  • Cuboid
  • Nearly equal length and width
  • Most wrist and ankle bones
• Irregular Bones


  • Complex shapes
  • Examples: vertebrae, some facial bones
• Flat Bones


  • Thin
  • Afford considerable protection
  • Provide extensive surfaces for muscle attachment
  • Examples: cranial bones, sternum, ribs, scapulae
• Sesamoid Bone


  • Patella
• Parts of a Long Bone

  • Diaphysis (bone shaft or body)
  • Epiphyses (distal and proximal ends of the bone)
  • Metaphyses (regions where diaphysis joins the epiphyses)
  • Epiphyseal (growth) plate
  • Articular cartilage
  • Periosteum
  • Medullary cavity
  • Endosteum
• Epiphyseal (growth) plate


  A layer of hyaline cartilage that allows the diaphysis of the bone to grow in length
• Epiphyseal line


  Cartilage in the epiphyseal plate is replaced by bony structure when bone growth in length stops
• Articular cartilage


  A thin layer of hyaline cartilage covering the part of the epiphysis that forms an articulation (joint) with another bone
• Periosteum


  A tough sheath of dense irregular connective tissue and its associated blood vessels that surround the bone surface when it's not covered by articular cartilage
• Medullary cavity


  A hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow in adults
• Endosteum


  A thin membrane that lines the medullary cavity and contains a single layer of bone forming cells
• Extracellular matrix


  About 25% water, 25% collagen fibres, and 50% crystallised mineral salts
• Calcification


  The process of mineral salt deposits in the framework formed by the collagen fibres of the extracellular matrix, initiated by osteoblasts
• Bone Cells


  • Osteoprogenitor cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteoprogenitor cells


  Stem cells that develop into osteoblasts
• Osteoblasts


  Cells that synthesize and secrete the extracellular matrix that calcifies into "bone"
• Osteocytes


  The most numerous cells in bone tissue, maintain bone tissues
• Osteoclasts


  Cells that break down extracellular matrix to release nutrients, help bones grow, and heal
• Compact Bone


  • Denser and arranged in osteons
  • Each osteon has an osteonic canal for blood supply and rings of concentric lamellae
  • Within the lamellae are the tiny lacunae, where osteocytes live
• Spongy Bone


  • Has no osteons and is arranged irregularly in trabeculae
  • Cavities are filled with red bone marrow
• 80% of the skeleton is compact bone (for strength and protection) and 20% is spongy bone (for lightness)
• Ossification (Bone Formation)


  • Initial formation of bones in an embryo and fetus
  • Growth of bones during infancy, childhood, and adolescence until their adult sizes are reached
  • Remodeling of bone (replacement of old bone tissue by new bone tissue throughout life)
  • Repair of fractures (breaks in bones) throughout life
• Intramembranous ossification


  Bone forms directly within mesenchyme that is arranged in sheetlike layers that resemble membranes
• Endochondral ossification


  Bone forms within hyaline cartilage that develops from mesenchyme
• Intramembranous Ossification


  1. Ossification centres where osteoblasts differentiate and begin secreting bone matrix

  2. Calcification as osteocytes extend out into the osteon's canaliculi and deposit minerals that calcify (harden into more matrix)

  3. Trabeculae formation creates spongy bone with abundant blood vessels and red bone marrow

  4. Periosteum development around the periphery of the spongy bone creates a compact bone to surround the underlying spongy bone
• Endochondral Ossification


  1. Cartilage model development as chondroblasts secrete cartilage matrix to form a cartilage model

  2. Cartilage model growth as the matrix calcifies and chondroblasts die, creating lacunae

  3. Primary ossification center develops as a blood vessel stimulates cells to become osteoblasts, replacing cartilage matrix with bone matrix

  4. Medullary cavity develops as osteoclasts digest spongy bone to form the medullary cavity inside the diaphysis

  5. Secondary ossification centers form as blood vessels enter the epiphyses, and ossification travels from the inner to the outer surface
• Spongy bone


  • Abundant blood vessels and red bone marrow
• Periosteum development


  Creates a compact bone to surround the underlying spongy bone
• Intramembranous ossification


  Bone formation where bone develops directly from mesenchymal tissue without a cartilage model
• Endochondral ossification


  1. Cartilage model development

  2. Cartilage model growth

  3. Primary ossification center develops

  4. Ossification grows exponentially towards both ends of the cartilage model
• Endochondral ossification


  • Medullary cavity develops
  • Secondary ossification centers form
  • Articular cartilage forms
  • Epiphyseal plate is the "growth plate" for long bones
• Bone growth in length


  1. Chondrocytes at the epiphyseal plate reproduce faster than they are calcified by bone

  2. As adolescence ends, bone replaces cartilage and the bone is at its final length
• Bone growth in thickness

  1. Perichondrium cells become osteoblasts which lay down bone matrix before becoming osteocytes

  2. Osteocytes create new osteons and thicken the bone
• Intramembranous ossification


  Formation of flat bones
• Endochondral ossification


  Formation of long bones