Homeostasis: Maintaining the Internal Environment (SL IB Biology)

• The process of maintaining a constant internal environment is known as homeostasis
• Homeostasis ensures that conditions inside the body are kept within preset limits
• Homeostasis is critically important for organisms as it ensures the maintenance of optimal conditions for enzyme action and cell function
• Sensory cells can detect information about the conditions inside and outside the body; if conditions have changed then the body can respond to keep conditions constant
• Examples of physiological factors that are controlled by homeostasis in mammals include
  • Core body temperature
  • Blood pH
  • Concentration of glucose in the blood
  • Osmotic concentration of the blood

• The majority of homeostatic control mechanisms in organisms use negative feedback loops to achieve homeostasis
• Negative feedback mechanisms work to return values to a set point; they reverse the effects of any change within a system
  • Negative feedback loops are essential for maintaining conditions within set limits; this is not the case in positive feedback mechanisms which instead amplify any change
• Negative feedback control loops involve:
  • A receptor – receptor cells detect change in a physiological factor
  • A coordination system – the brain and nervous system transfer information between different parts of the body
  • An effector – the muscles and glands bring about a response
• Outcome of a negative feedback loop:
  • The factor / stimulus is continuously monitored
  • If there is an increase in the factor, the body responds to make the factor decrease
  • If there is a decrease in the factor, the body responds to make the factor increase

Negative feedback loops maintain conditions to a set point