1. Negative feedback loops

2. What are the stages in a negative feedback loop? Set point – Desired/normal level Receptor – Detects deviation from set point Controller – Coordinates info Effector – Carrys out corrective measures to bring back to set point Feedback loop – Informs receptor of changes to system

3. Negative feedback system – Water bath Input Change to the system Receptor Measures level of a factor Control unit Operational information is stored here and used to coordinate effectors Effector Brings about changes to the system in order to return it to the set point Output System returned to set point Feedback loop

4. Negative feedback Causes corrective measures to be turned off therefore returning system to its normal levels In reality the receptors detect the change and stop sending impulses to the controller, switching the corrective measures off

5. Negative feedback system – Water bath Input Change to the system Receptor Measures level of a factor Control unit Operational information is stored here and used to coordinate effectors Effector Brings about changes to the system in order to return it to the set point Output System returned to set point Feedback loop TASKS: Draw feedback loops for … Increase in temperature Decrease in temperature Increase in blood glucose Decrease in blood glucose

6. Positive feedback When corrective measures cause the feedback mechanism to stay switched on TASK Describe 3 examples of positive feedback (pg 214)

7. Control of the oestrous cycle Start activity: What are the 4 main hormones involved in the oestrous cycle?

8. What is the oestrous cycle? A recurring cycle in women that takes 28 Days involving… Release of an egg from the ovary Changing the thickness of the uterus lining Shedding the uterus lining if pregnancy doesn’t occur This is controlled by several hormones…

9. Oestrogen: Causes the lining of the uterus to thicken and grow Stimulates the release of an egg at day 14 Progesterone: Maintains the lining of the uterus When the level of progesterone falls the lining breaks down TASKS 1) Copy the above notes 2) Use this information to complete the work sheet