Feedback Mechanisms

Big Idea #2: Biological systems use energy to grow, reproduce, and maintain dynamic homeostasis.

Essential Knowledge

• 2C1: Organisms use feedback mechanisms to maintain their internal environments and

respond to external 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

• Returns a changing condition back to its target set point.

• Ex: Return body to normal conditions

Negative

Feedback –

Hot!!

• Beckham sweats b/c he is hot (literally) Sweat evaporates, removing heat Becks cools down!

• Cold means Becks is losing heat shivers/ shakes to generate heat His body goes through cellular respiration to convert sugar/fat (like he has any) heat blood is diverted from skin Stops losing heat!

Negative

Feedback –

COLD!!

Body Example: Glucose

• 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

When Feedback Goes Wrong…

Body Example: Water

• When you have too much water pee it out (ANF)

• When you need to save 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

Ex: Birth• Contractions start More contractions

leads to more release of oxytocin Leads to more contractions (frequent and stronger) PUSH!