homeostasis

• Homeostasis is the maintenance of a constant internal environment. 
• There are fluctuations but are maintained around an optimum point to balance equilibrium.  
• Conditions that are maintained:

  • pH 
  • Temperature 
  • Water potential 
  • Blood glucose concentration 
• pH chemoreceptors found in the walls of the carotid artery, decreases are detected due to a build up of CO2 and lactate. The oblongata medulla tells the heart to increase its rate and to increase the breathing rate. 
• pH is controlled to prevent enzyme and protein denature. 
• Temperature is controlled to prevent enzyme denature, to aid transport systems. 
• Water potential is controlled to maintain concentrations of solutes in cells. 
• Blood glucose concentration is controlled to ensure there is enough substrates for respiration and to maintain water potential. 
• Each cell is bathed in tissue fluids which supply nutrients and remove wastes. This fluid must be maintained to protect cell from external environment changes. 
• Negative feedback return systems to equilibrium. Most systems are negative feedback. 
• Negative feedback:

  • When a stimulus causes the corrective measures to be turned on this results in a return to the optimum and equilibrium is maintained. 
  • Negative feedback of hormones, when a particular hormone is released it causes the reduction of secretion in that hormone. 
• Use of separate feedback systems improve the control over conditions. 
• Examples of negative feedback:

  • Thermoregulation - temperature 
  • Glucoregulation - glucose 
  • Osmoregulation - fluid and ion balance 
• Positive feedback systems increase the rate of the initial stimulus/change. Positive feedbacks are rare in biology because it produces unstable conditions. 
• Positive feedback example:

  • Influx of sodium ions at a neurone causes more sodium ion voltage gated channels to open 
  • Hypothermia - the temperature control system breaks down causing body temperature to drop further 
  • Contractions during childbirth triggered by oxytocin which stimulates more contractions.