Response to Environmental Changes Feedback Mechanisms Response to Environmental Changes

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

Feedback Mechanisms Responses to environment to maintain homeostasis

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

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!

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

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.

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

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

When Feedback Goes Wrong… Bad things happen!

Type 2 Diabetes Individuals who eat a lot of sugar have very high levels of insulin in the blood Over time cells stop responding to insulin (perhaps an evolutionary mechanism?) Leads to excess sugar in the blood- sugar gets into eye, damages blood vessels, damages kidney etc.

Body Example: Water When you have too much water, you pee it out (ANF) When you need to conserve water anti- diuretic hormone (ADH) is released Concentrates urine, decreases sweating, inhibits water loss, increases water absorption

Positive Feedback Response to the stimulus is amplified i.e. you eat an appetizer, that makes you more hungry so you eat more food

I.e. 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

Positive vs. Negative