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

• Hormone that causes cells to take in glucose

• Lowers blood glucose levels

• Triggered by high blood glucose levels

Glucagon

• 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