1. BELLWORK – 2/4/2014
1. Read pages in your review book on FEEDBACK and HOMEOSTASIS.
2. Read and discuss QUIETLY the ESSENTIAL question below with your table partner (be prepared to explain if called upon):
During hot weather and vigorous exercise, people sweat. As the water on their skin evaporates, the water molecules absorb heat energy.
Explain why this process is important to the individual.

2. Dynamic Equilibrium
Our bodies are constantly responding and adjusting to external and internal stimuli, causes small changes in our body temperature, blood sugar level, etc.
We refer to these small changes as dynamic equilibrium. This allows us to maintain homeostasis (internal balance).
All living things must maintain homeostasis in order to survive. EX. Human body temp is 37 C; if temp is altered, processes that keep us going will begin to fail

3. Dynamic Equilibrium
Constant small corrections that keep internal environment w/in stable limit
AFTER MEAL
BODY TEMP
BLOOD SUGAR LEVEL
TIME
TIME

4. FEEDBACK MECHANISMS Help regulate the endocrine system
Maintain homeostasis
Let’s watch:

5. TYPES OF FEEDBACK MECHANISM
1. Negative Feedback
Stimulus
Reaction
Response
Negative Feedback
 considered negative because the original signal is lowered or shut off.

6. Examples OF FEEDBACK MECHANISM
EX: Thermostat
Ex. Body Temperature
ROOM
COOLS
DOWN
FURNACE
KICKS ON
WARMS UP
OFF
Stimulus: Brain senses a drop in blood temperature.
Reaction: Nerve message sent to muscles to start shivering.
Response: Heat is generated that warms the body and blood.
Negative Feedback: Warmer blood triggers brain to turn-off shivering.

7. Example 3: Glucose levels in the blood
Blood sugar regulation by insulin (secreted by pancreas)
Video: Insulin, Glucose and you

8. Ex 4. Plants regulating water loss
Guard cells in plants opening and closing to prevent water loss

9. Response: Baby is born and the feedback cycle ends.
2. Positive Feedback Mechanism – Change in system  causes greater change or response
Stimulus: A contraction pushes the baby’s head against the base of the uterus.
Reaction: Pressure on the base of the uterus causes stronger contractions.
Response: Baby is born and the feedback cycle ends.
Positive Feedback