1. FEEDBACK MECHANISMS & HOMEOSTASIS

2. HOMEOSTASIS Maintaining the internal environment within a stable range given factors that influence the external environment Homeostasis controls many aspects of the internal environment, for example: Body temperature Blood concentrations of: glucose, hormones, carbon dioxide and ions Oxygen levels Blood pH Blood pressure Solute concentration (Water balance)

3. FEEDBACK MECHANISMS Maintain homeostasis by detecting and responding to a stimulus A non-biology example:

4. NEGATIVE FEEDBACK Reduces the size of the stimulus to restore homeostasis Temperature regulation Blood glucose Blood pressure Stimulus  effector  response

5. NEGATIVE FEEDBACK: HUMANS Protein receptor on cells surface takes up insulin

6. BLOOD PRESSURE NEGATIVE FEEDBACK A. stimulus – exercise increases blood pressure B. receptor gets the message to the (C) control center. D. The effector, the heart, pumps blood slower & E. blood vessels dilate & get wider to allow blood to pass through). F. Homeostasis is obtained

7. NEGATIVE FEEDBACK: PLANTS

8. POSITIVE FEEDBACK - CHILDBIRTH

9. POSITIVE FEEDBACK Response increases the original stimulus to restore homeostasis Rarely used Only normal when there is a definite end point Childbirth Blood clotting