1. KEY CONCEPT Biology is the study of all forms of life.

2. Conditions within the body must remain within a narrow range in order for organisms to stay alive.
Homeostasis is the regulation and maintenance of the internal environment of living things.
Homeostasis involves keeping the internal environment within set ranges.
Example: Body temperature.
Cold temperatures can lead to goose bumps.
Blood flow to the skin decreases. Tiny muscles contract the pores and the skin around body hairs conserve heat.

3. Organisms must maintain homeostasis to survive in diverse environments.
Predict: What will happen to the skin in hot temperatures?
Draw conclusions: Why is it so important to maintain homeostasis within the body?

4. Control systems help maintain homeostasis. sensors gather data
control center receives data, sends messages
communication system delivers messages to target organs, tissues
targets respond to change
pore
sweat
glands
hair
follicle
muscle
goose
bump

5. Homeostasis is usually maintained through negative feedback.
Negative feedback systems return a condition to its normal (set) point.
Most functions in the body are regulated by negative feed back loops
Examples: Respiratory rates, thermoregulation, blood sugar levels, hunger and thirst levels, water levels

6. Negative feedback loops are necessary for homeostasis.
Feedback compares current conditions to set ranges.
Negative feedback counteracts change.
Negative Feedback Loop
O2 / CO2 level returns to normal
Holding breath, CO2 levels rise,
Control system forces exhale, inhale

7. Positive feedback increases change.
Torn vessel stimulates release of clotting factors
platelets
fibrin
white blood cell
red blood cell
blood vessel
clot
Growth hormones stimulate cell division
The release of hormones to stimulate labor in humans.

8. A disruption of homeostasis can be harmful.
Homeostasis can be disrupted for several reasons.
sensors fail
targets do not receive messages
injury
illness

9. Short-term disruption usually causes little or no harm.
Effects usually last a few days or a few weeks. Example: cold or flu virus
Long-term disruptions can cause more damage.
Example: Diabetes is a serious long-term disruption of homeostasis. 1 2 3 4
Pancreas cells attacked;insulin declines
Blood glucose levels rise,
Body burns fat; blood more acidic,
Cells impaired; all organs damaged.
pancreas
fats
kidneys

10. Behaviors and adaptations can help maintain homeostasis.
Behavior: If you are cold, put on a jacket.
Adaptation – polar bears have hollow hair.
Summarize: What is homeostasis and why is it important?
Fig 2.3 – The polar bear can maintain homeostasis in very cold climates. Its hollow hair is one adaptation that helps the bear retain its body heat. SEM Magnification: 450X