Homeostasis

• What is homeostasis?

  Internal environment is maintained within set limits around an optimum
• Why is it important that core temperature remains stable?


  Maintains stable rate of enzyme controlled reactions & prevent damage to membranes and proteins
• Why is it important that blood glucose concentration remains stable?

  • Maintains constant blood water potential - prevent osmotic lysis of cells
  • Maintain constant concentration of respiratory substrate
• Define negative and positive feedback?

  • Negative feedback - Mechanisms that return internal environment to optimum when there is a fluctuation
  • Positive feedback - A fluctuation triggers amplified changes that result in a deviation from normal levels
• hypothalamus contains thermoregulatory centre with receptors sensitive to temperature of the blood
• thermoregulatory centre receives nervous impulses from thermoreceptors in skin, impulse sent along motor neurone to effectors
• • too hot, sweat glands release more sweat, sweat evaporates, heat energy released to environment (cooling effect)
• • too hot, blood vessels dilate, more blood flow through skin capillaries, more heat lost from skin (vasodilation)
• • too hot, nerve impulses sent to hair erector muscles in skin which relax, skin hairs lie flat,(pilorelaxation)
• 1. too cold, skeletal muscles contract rapidly(shivering), energy required for contraction from respiration, heat released warms body
• 2. too cold, blood vessels constrict, less blood flow to skin capillaries, conserves body core temperature (vasoconstriction)
• 3. too cold, nerve impulses are sent to hair erector muscles in skin which contract, raises skin hairs, traps air for insulation (piloerection)
• animals change behavior to regulate body temperature e.g. seek shade, cool off in water, reduce activity
• some organisms increase or decrease surface area to increase or decrease heat loss through conduction