Skeletal System

• Skeletal System


  Bones and Joints
• Components of the Skeletal System

  • Bones
  • Cartilage
  • Tendons
  • Ligaments
• Functions of the Skeletal System

  • Body support
  • Organ protection
  • Body movement
  • Mineral storage
  • Blood cell production
• Connective tissues


  Bone, cartilage, tendons, and ligaments of the skeletal system
• Bone remodeling


  Cells break down to produce and replace with new matrix
• Collagen


  Fibrous protein that provides flexibility but resists pulling or compression
• Proteoglycans


  Water trapping proteins that help cartilage to be smooth and resilient
• Characteristics of connective tissues are determined by the composition of extracellular matrix
• Bone matrix


  35% organic and 65% inorganic material
• Organic material in bone matrix

  • Collagen
  • Proteoglycans
• Inorganic material in bone matrix

  Calcium, phosphate crystal— hydroxiapatite
• Mineral component


  Gives bone compression strength
• Brittle bone disease


  Imperfect bone formation
• Bone cells


  • Osteoblasts
  • Osteocytes
  • Osteoclasts
• Osteoblasts


  Bone building cells
• Ossification


  Formation of new bone
• Osteocytes


  Maintain bone matrix and form from osteoblast after bone matrix has surrounded it
• Osteoclasts


  Bone-destroying cells
• Bone reabsorption


  Osteoclasts remove existing bone and mobilize Ca2 that goes into the blood
• Ruffled border


  Specialized reabsorption-specific area of osteoclast membrane
• Spongy bone


  Less bone matrix and more space
• Trabeculae


  Interconnecting rods or plates of bone that has spaces in between filled with bone marrow and blood vessels
• Compact bone


  More bone matrix and less space
• Osteon


  Functional unit of compact bone
• Central canal


  Surrounded by concentric rings of matrix where blood vessels are contained
• Structure of Long Bone

  • Diaphysis
  • Medullary cavity
  • Epiphyses
  • Articular cartilage
  • Epiphyseal plate
  • Epiphyseal line
• Bone marrow


  Soft tissue that fills the cavities in spongy bone and medullary cavity in diaphysis
• Types of bone marrow

  • Red marrow
  • Yellow marrow
• Periosteum


  Connective tissue membrane that cover outer surface of a bone
• Endosteum


  Single cell layer of connective tissue that lines the internal surfaces of all cavities within bones
• Bone formation patterns in the fetus

  • Intramembranous ossification
  • Endochondral ossification
• Intramembranous ossification


  1. Osteoblasts begin to product bone within connective tissue membranes

  2. Spongy bone formation

  3. Compact bone formation
• Endochondral ossification


  1. Cartilage model formation

  2. Bone collar formation

  3. Primary ossification center formation

  4. Secondary ossification center formation

  5. Adult bone
• Bones cannot grow by interstitial growth, they increase in size only by appositional growth
• Bone length increase


  Increase at the epiphyseal plate
• Bone remodeling


  Replacing old bones with new bones
• Bone fracture repair


  1. Hematoma formation

  2. Callus formation

  3. Callus ossification

  4. Bone remodeling
• Calcium


  Critical nutrient involved in many physiological processes
• Calcium homeostasis


  1. Moves in as osteoblasts

  2. Moves out as osteoclasts

  3. Maintained by Parathyroid hormone and Calcitonin
• Parathyroid hormone


  Secreted by parathyroid gland, increases formation and activation of osteoclasts which stimulates reabsorption of Ca2 form urine in kidney, indirectly increases Ca2 uptake from the small intestine through the activation of calcitriol