2. What is Homeostasis?
• process by which a constant internal environment is maintained despite changes in external environment
• performed by the endocrine and nervous systems

3. Dynamic Equilibrium
• State of balance achieved by continuous adjustments in response to internal or external environments
eg. Healthy people maintain:
blood glucose conc. at 100 mg/ml
blood pH near 7.4
blood pressure at 120/80 mm Hg
body temperature of 37°C

4. Feedback Loops Negative Feedback • systems designed to resist change
• a process where a mechanism detects when conditions are different from normal (homeostasis) and works to restore normal body constraint

7. Homeostatic Control System
Receptor – organ / tissue that detect changes that are not within “normal” range
Control Centre – organs which process info from the receptors and send signals to another part of the body
Effector – organ / tissue which will adjust the original changes to a normal range

9. Investigating Homeostatic Feedback Mechanisms
Question: How does our body respond to temperature extremes?
Predict: How will a hand placed in ice cold water compare with a hand placed in hot water?
Explain:
Observe!
Explain.
Hand in ice water
Hand in warm water

11. Positive Feedback • act to increase the strength of a stimuli
• not common; moves system away from homeostasis
(usually disastrous causing serious health issues)
e.g.: Childbirth, Fight or Flight
- pressure of baby’s head on cervix stimulates hypothalamus in brain to make hormones that causes contractions; more pressure produce more hormone and more contractions...

12. Homework
1. Read 9.1 & 9.2
2. Complete pg 435 # 1-4, 7, 13