1. Response to Environmental Changes
Feedback Mechanisms
Response to Environmental Changes

2. Dynamic Homeostasis Living things maintain stable internal conditions
Examples in humans:
Temperature pH
Solute concentrations (Ca, Fe, Salt, Glucose etc.)
Heart rate/blood pressure/Breathing rates
Oxygen/CO2 concentrations

3. Feedback Mechanisms
Responses to environment to maintain homeostasis

4. Negative Feedback Return body to normal conditions
I.e. when it’s hot, we cool ourselves down
When it’s cold, we heat ourselves up
Most things in the body are negative feedback
Negative- will eventually shut off when it reaches a limit

5. Negative Feedback - Hot
It is warm out
You sweat
Sweat evaporates, removing heat
You are more lethargic
Blood flows to your skin to release heat
You cool down!

6. Negative Feedback - Cold
It is cold, you are losing heat
You shiver/shake to generate heat
Your body goes through cellular respiration to convert sugar/fat  heat
Your blood is diverted from the skin
You stop losing heat

7. Body Example: Glucose Your blood sugar level is extremely important
High blood sugar levels long term cause cell/organ damage
Low blood sugar leads to fatigue, impaired functioning, fainting, brain damage etc.

8. Pancreatic Regulation
Insulin
Glucagon
Hormone that causes cells to take in glucose
Lowers blood glucose levels
Triggered by high blood glucose levels
Hormone that raises blood sugar levels (breaks down glycogen into glucose)
Triggered by low blood sugar

9. Insulin/Glucagon System
Blood sugar high  Insulin release Blood sugar low  Glucagon release
After you eat- more insulin release
Between meals – more glucagon release

11. When Feedback Goes Wrong…
Bad things happen!

12. Positive Feedback Response to the stimulus is amplified
i.e. you eat an appetizer, that makes you more hungry so you eat more food
Can’t stop, won’t stop!

13. Example: Birth Contractions start
More contractions lead to more release of oxytocin
More oxytocin leads to more contractions (more frequent and stronger)
Leads to more oxytocin  Stronger contractions  Birth