Physiology -Chap 6.2- Outline

Bone Scan

• A diagnostic procedure
  
  • Takes advantage that bone is living tissue
    
  • Radioactive tracer is absorbed by bone is injected
    
  • Measures radiation emitted by bone
    
    • X-Ray
      
• Normally appear as gray
  
  • Darker-hot spot-increased metabolism
    
  • Lighter-cold spot-decreased metabolism
    

  Bone and Nerve Supple of Bone
  

• Blood vessels pass into bone from periosteum
  
• Arteries
  
  • Periosteal
    
    • Enter the diaphysis through perforating canals
      
    • Supply periosteum and outer part of compact bone
      
  • Nutrient
    
    • Passes through hole in compact bone called nutrient foramen
      
    • Divides into proximal and distal branches
      
    • Supply the inner part of compact bone tissue and spongy bone tissue and red marrow
      

  (Long bones supplied by matephyseal plate and epiphyseal arteries
  

  Arise from arteries that supply the associated joint)
  

  • Metaphyseal
    
    • Enter the metaphyses with nutrient artery
      
    • Supply RBM and bone tissue of metaphyses
      
• Veins
  
  • Nutrient Veins
    
    • Accompany nutrient artery in the diaphysis
      
  • Epiphyseal & Metaphyseal
    
    • Exit in epiphyses
      
  • Periosteal
    
    • Exit with respective arteries in the periosteum
      
• Periosteum
  
  • Rich in sensory nerves
    
    • Carry pain sensations
      
    • Sensitive to tearing or tension
      

      
      

  Bone Formation
  

• Ossifacation/ Osteogensis
  
  • Formation of bone
    
• Skeleton of embryo
  
  • Composed of loose mesechymal cells
    
    • Shaped like bones
      
    • Provide template for subsequent ossifacation
      
• Methods of ossifacation
  
  • Intramembranous
    
    • Bone forms directly within mesenchyme arrange in sheet-like layers
      
      • Resembles membranes
        
  • Endochondral
    
    • Bone forms within hyaline cartilage that develops from mesenchyme
      

  Intramembranous Ossification
  

• Simpler
  
• Skull and jaw formed this way
  
• Hardening of fetal skull:
  
  • Development of ossifacation center
    
    • Chemical message causes mesenchymal cells to cluster and differentiate
      
    • Osteoblasts secrete organic EC-M until they are surrounded
      
  • Calcification
    
    • Secretion of EC-M stops and osteocytes lie in lacunae and extend cytoplasmic processes into canaliculi that radiate in all directions
      
    • In a few days it all hardens
      
  • Formation of Trabeculae
    
    • EC-M develops into trabeculae
      
      • Fuses with one another to form spongy bone
        
  • Development of the Periosteum
    
    • Mesenchyme condenses and develops into periosteum
      
    • Thing layer of compact bone replaces surface of spongy bone
      
    • Much of newly formed bone is remodeled as bone is transformed into its adult size and shape
      

  Endochondral Ossifacation
  

• Replacement of cartilage by bone
  
• Process:
  
  • Development of the Cartilage Model
    
    • Chemical messages cause mesenchymal calls to crowd in the shape of the future bone
      
    • Develop into chondroblasts
      
      • Secrete EC-M
        
      • Produce cartilage model
        
      • Perichondrium membrane develops around it
        
  • Growth of the Cartilage Model
    
    • Model grows further by continual cell division of chondrocytes and further secretion of EC-M
      
      • Called interstitial growth
        
      • Results in an increase of length
        
    • Thickness due to addition of EC-M material
      
      • Appositional growth
        
    • Chondrocytes and surroundings EC-M calcifies
      
  • Development of the Primary Ossifacation Center
    
    • Proceeds inward from external surface of bone
      
    • Nutrient artery penetrates perichondrium, and cart. Model
      
      • Stimulates osteogenic cells to differentiate into osteoblasts
        
    • Once perichondrium starts of form the bone it's known as periosteum
      
    • Growth
      of primary ossifacation center
      
      • Where bone tissue replaces cart.
        
    • Start of formation of spongy bone tabeculae
      
  • Development of the Medullary Cavity
    
    • Osteoclasts break down newly formed spongy bone trabeculae
      
      • Leaves a cavity in the diaphysis
        
        • Eventually replaced by compact bone
          
  • Development of the Secondary Ossifacation Centers
    
    • Formed when epip. artery enter the epiphyses
      
    • Spongy bone remains in the interior
      
    • Proceeds outward
      
  • Formation the Articular Cartilage and the Epiphyseal Plate
    
    • Hyaline cart. that covers the epiphyses becomes the articular cart.
      
    • Epiphyseal plate=Responsible for lengthwise growth of long bones
      

  Bone Growth
  

  Growth in Length
  

• Epiphyseal contains for layers:
  
• Zone of Resting Cartilage
  
  • Consists of small scattered chodrocytes
    
  • Cells do not function in growth
    
    • Anchor to epiphyseal plate to the epiphyses of the bone
      
• Zone of Proliferating Cartilage
  
  • Chondrocytes arranged in stacks
    
    • They divide to replace those that die at the diaphyseal side
      
• Zone of Hypertrophic Cartilage
  
  • Consists of large maturing chondrocytes arranged in columns
    
• Zone of Calcified Cartilage
  
  • Only a few thick
    
  • Consists of dead chondrocytes
    
    • Dead by calcified EC-M
      
• At maturation plate fades leaving the bony structure called the epiphyseal
  line
  

  Growth in Thickness
  

• Appositional growth:
  
  • Cells in the periosteum differentiate into osteoblasts
    
    • Secrete collagen fibers and other molecules that form EC-M
      
    • Become surrounded by EC-m and turn into osteocytes
      
      • Forms ridges
        
  • Ridges fold together and fuse
    
    • Groove become tunnel that encloses blood vessel
      
    • Periosteum=endosteum
      
  • Osteoblasts deposit bone EC-M
    
    • Forms new concentric lamellae
      
      • Proceeds inward
        
  • Ostoblasts under periosteum deposit new outer circumferential lamellae