homeostasis

• Function of molecules, cells, tissues, organs and systems of the human body


  Relevant to the practice of dentistry
• Integration of human body systems


  In homeostasis
• Homeostasis


  Process of bringing a disrupted system to normal state
• Homeostasis


  1. Intake of nutrients and oxygen

  2. Produce waste and CO2
• Cells


  • Require the internal environment
  • Have basic metabolic activity
• Organs


  • Have many cells
  • Need to present nutrients and oxygen to cells
  • Need to remove waste and CO2
• Body systems


  • Systems that interact with external environment and expend energy (nervous, locomotor, reproductive)
  • Systems that interact with internal environment and help achieve homeostasis (cardiovascular, respiratory, excretory, alimentary)
  • Systems that control other systems (nervous, endocrine)
• Importance of homeostasis

  • Cells function most effectively under 'optimal' environmental conditions
  • Basic cellular functions tend to alter their immediate environment
  • Homeostasis operates to correct any changes in the cellular environment
• Enzyme


  Biological catalyst that transforms one component to another, usually protein
• Conditions important for homeostasis

  • Temperature
  • pH
  • Oxygen concentration
  • CO2 concentration
• Homeostasis control

  • Feed-back control
  • Feed-forward control
• Negative feedback control


  1. A change in a variable activates mechanisms that alter the level of that variable so as to counteract the change

  2. Tends to maintain the status quo
• Set point


  The level a variable is maintained at, can change
• Thermoregulation


  Shaking/shivering when cold to produce energy
• 'Circa' means around, 'dian' means day
• Other rhythms include menstrual cycle, yearly cycle, metabolism
• Feedforward control


  • Altering a behaviour before there is an obvious 'error signal'
  • Anticipatory action
• Positive feedback


  • A change in a variable activates mechanisms that alter the level of that variable so as to increase the change
  • Not used in homeostatic control
  • Potentially disruptive
• Fluid compartments


  • Extracellular fluids (interstitial, plasma)
  • Intracellular fluids
• Osmosis


  Water movement occurs by osmosis, along its concentration gradient

  
• Homeostasis does not keep every variable at a constant level all the time
• There is a range of values which is considered 'normal'
• Some body 'variables' do not change, for example a person's height

  
• The 'normal range' of heights differs in every country as different averages