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
  • Examples: most wrist and ankle bones
• Irregular Bones


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


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


  • Patella
• Macroscopic Structure of Long Bone

  1. Diaphysis (bone shaft or body)

  2. Epiphyses (distal and proximal ends of the bone)

  3. Metaphyses (regions where diaphysis joins the epiphyses)

  4. Epiphyseal (growth) plate (layer of hyaline cartilage that allows diaphysis to grow in length)

  5. Articular cartilage (thin layer of hyaline cartilage covering epiphysis)

  6. Periosteum (tough sheath of dense irregular connective tissue and associated blood vessels)

  7. Medullary cavity (hollow, cylindrical space within diaphysis containing fatty yellow bone marrow)

  8. Endosteum (thin membrane lining medullary cavity)
• Extracellular Matrix of Bone

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


  Hardening of bone due to mineral salt deposits in the collagen fibre framework
• Osteoblasts


  Bone building cells that initiate calcification
• Bone Cells


  • Osteoprogenitor cells
  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Compact Bone


  • Denser, arranged in osteons with osteonic canals, concentric lamellae, and lacunae
  • 80% of skeleton
• Spongy Bone


  • Less dense, arranged irregularly in trabeculae, filled with red bone marrow
  • 20% of skeleton
• Ossification (Bone Formation)


  1. Initial formation of bones in embryo and fetus

  2. Growth of bones during infancy, childhood, and adolescence

  3. Remodeling of bone throughout life

  4. Repair of fractures throughout life
• Intramembranous Ossification


  1. Ossification centres

  2. Calcification

  3. Trabeculae formation

  4. Periosteum development
• Endochondral Ossification


  1. Cartilage model development

  2. Cartilage model growth

  3. Primary ossification center

  4. Medullary cavity development

  5. Secondary ossification centers
• Spongy bone


  • Abundant blood vessels and red bone marrow
• Periosteum development


  Around the periphery of the spongy bone creates a compact bone to surround the underlying spongy bone
• Intramembranous ossification


  Bone formation process where bone is formed directly from mesenchymal cells without a cartilage model
• Endochondral ossification


  Replaces cartilage with bone matrix for most bones
• Endochondral ossification


  1. Cartilage model development

  2. Cartilage model growth

  3. Primary ossification center development

  4. Ossification growth towards both ends
• Endochondral ossification


  1. Medullary cavity development

  2. Secondary ossification centers form

  3. Articular cartilage forms

  4. Epiphyseal plate forms
• Bone growth in length

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

  2. Bone replaces cartilage at end of adolescence
• 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
• Bone remodeling


  1. Bone resorption by osteoclasts

  2. Bone deposition by osteoblasts
• Bone remodeling occurs naturally through life as exercise, diet, and lifestyle require the body to change bone density, thickness, and mineral availability
• Factors required for bone growth, repair, and remodeling

  • Adequate minerals for bone matrix (calcium, phosphorus, and magnesium)
  • Vitamins A, C, and D
  • Hormones
  • Weight-bearing exercise that places stress on bones
• Parathyroid hormone (PTH)


  Secreted by parathyroid glands, promotes bone resorption by osteoclasts, enhances recovery of calcium ions from urine, promotes formation of active form of vitamin D (calcitriol)
• Calcitonin (CT)


  Secreted by thyroid gland, inhibits bone resorption by osteoclasts
• Exercise


  Weight-bearing activities stimulate osteoblasts and help build thicker, stronger bones and retard loss of bone mass that occurs as people age
• Aging


  As the level of sex hormones diminishes during middle age to older adulthood, especially in women after menopause, bone resorption by osteoclasts outpaces bone deposition by osteoblasts, which leads to a decrease in bone mass and an increased risk of osteoporosis
• Parathyroid hormone acts directly on bone


  Stimulates resorption and release of Ca2+ into the extracellular space
• Parathyroid hormone acts directly on kidney


  Increases calcium reabsorption and phosphate excretion
• Cranial bones


  • Frontal, sphenoid, ethmoid, occipital, parietal and temporal bones
  • Function: protect brain
• Facial bones


  • Zygomatic, lacrimal, nasal, inferior nasal conchae, palatine, maxilla, vomer, mandible
  • House the orbits of the eyes, the nasal and oral cavities, and the sinuses