1. Feedback and Homeostasis
Vocab terms to define:
Feedback mechanism
Dynamic equilibrium
Stimuli
Homeostasis
Pancreas
Insulin
Guard cells
Review book: Read pg questions completed on loose leaf paper

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. TYPES OF FEEDBACK MECHANISM
EX: Thermostat
Ex. Body Temperature
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.
ROOM
COOLS
DOWN
FURNACE
KICKS ON
WARMS UP
OFF

7. Example 3: Glucose levels in the blood
1. Blood sugar regulation by insulin (secreted by pancreas)
insulin -- a hormone (chemical messenger); lowers blood sugar 2 major ways:
Takes glucose into our cells to be used as fuel in cell respiration from our blood
Converts excess glucose to glycogen (animal starch) and stores it in our liver and muscles
glucagon -- convert glycogen back to glucose
2. The failure to maintain blood glucose homeostasis results in diabetes.

8. Ex #4: Plants regulating water loss
Guard cells in plants opening and closing the stomate to prevent water loss
Stomate- allows for exchange of water vapor (and gases) out of the leaf

9. Response: Baby is born and the feedback cycle ends.
2. Positive Feedback Mechanism – Change in system  causes a greater change or response; ex. labor
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

10. Body Systems for Maintaining Homeostasis in multicellular organisms
Excretory System - regulates the chemistry of body’s fluids while removing harmful wastes
Nervous System - uses electrical impulses to regulate body functions
Endocrine System - produces hormones (chemical messengers) regulating their behavior of the body
Immune System -stands guard with a set of defenses that protect the body from foreign invaders and disease