1. Introduction to Homeostasis

3. What is homeostasis? Homeostasis – a physiological steady-state maintained by the internal system despite outer external fluctuations Fluctuations may include… ◦…pH changes ◦…temperature changes ◦…a wild animal attack ◦…etc.

4. Why is homeostasis important? Homeostasis prevents changes that could damage cells It maintains constant conditions for chemical reactions to take place ◦What conditions influence chemical reactions?

5. Homeostatic mechanisms Your internal environment is regulated by: 1.Excretory system (kidneys) 2.Endocrine system (hormones) 3.Nervous system (brain & nerves)

6. Consider this… What happens physiologically when you exercise? ◦Increase in cell respiration ◦Oxidation of glucose = heat produced ◦Sweat produced ◦Loss of salts needed for nerve and muscle function ◦Loss of water = blood pressure drop ◦Heart and circulatory system must respond to blood pressure change That is A LOT of change just from moving around!

7. Control systems To maintain homeostasis, the body uses the following functional components in a feedback cycle ◦Monitor ◦Coordinating centre ◦Regulator

8. Control systems cont’d Various receptors/sensors in the body will register (monitor) fluctuations This information is conveyed to the brain (coordinating centre) Messages are then sent out to the appropriate regulator(s) that will ‘deal with’ the stimulus

9. Eg. Blood pressure change Normal range Monitor Coordinating centre Regulator adjustment eg. hemorrhaging causes drop in blood pressure eg. specific nerve cells in the brain eg. increase in heart rate eg. raises blood pressure

10. 1. What is the temperature range within the house over the time period shown? 2. What two values are used by the thermostat in its functioning? 3. At what temperature does the furnace turn on? At what temperature does it turn off? 4. In this scenario, what is the most likely value of the target temperature? Explain your reasoning. 5. What is the monitor, what is the coordinating centre and what is the regulator?

11. An experiment…