Homeostasis: Maintaining the Internal Environment (DP IB Biology): Revision Note

Maintaining the Internal Environment

• 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

Negative Feedback Loops

• 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