Homeostasis

• The hypothalamus is the control centre for homeostatic mechanisms
• Negative feedback loops are used by the body to maintain homeostasis, where changes from normal levels trigger responses that return the system back to its original state.
• Positive feedback loops can occur when there is no negative feedback mechanism present or it has been disrupted, leading to amplification of the initial stimulus until equilibrium is reached.
• For homeostasis to occur, the body needs to sense changes in the internal and external environment as well as compensate for these changes.
• The nervous and endocrine systems sense changes and control compensation for these changes. They help maintain homeostasis
• Homeostasis is maintained through feedback systems.
• Feedback Systems


  When the body responds to a stimulus (change), the response alters the original stimulus. Can be a positive or negative feedback system.
• Examples of Positive Feedback are oxytocin released during lactation, fever, blood clotting, childbirth
• Examples of negative feedback are blood sugar regulation, gas concentrations, osmoregulation and thermoregulation
• Stimulus


  Change in environment that causes a response.
• Receptor


  Detects the stimulus (change)
• Modulator


  Control centre that receives information from the receptor and sends it to the effector.
• Effector


  Causes the response – either counteracts or amplifies the effect of the stimulus.
• Response

  The effector’s reaction to stimulus.
• Feedback


  The original stimulus that has been changed by the response
• Homeostasis


  A process that involves nerves and hormones to maintain the body’s internal environment within its tolerance limits through the control of metabolism and physiological and behavioural activities
• Thermoregulation


  Occurs by the control of heat exchange and metabolic activity through physiological and behavioural mechanisms
• Blood sugar levels are maintained by controlling of sugar uptake, its storage and release by cells and use in metabolism; involves the hormones of the pancreas and adrenal glands
• Blood fluid concentrations are maintained by balancing water and salts via the skin, digestive system and the kidneys, which involve the actions of ADH and aldosterone in the nephron and the thirst reflex
• Gas concentrations are controlled by balancing the intake of oxygen and the removal of carbon dioxide via the lungs, through the actions of the medulla oblongata and the autonomic nervous system
• Negative Feedback


  feedback that reduces the effect of the original stimulus; involved in homeostasis
• Positive Feedback 


  Feedback that reinforces/ amplifies the original stimulus, which is not involved in homeostasis