Homeostasis & Feedback MechanismsLesson 1

Learning Goals

1. Define homeostasis

2. Feedback mechanisms components

3. Negative/Positive Feedback

Cold, Hot

Can we really tell?

Homeostasis �The physiological state in which the internal physical and chemical conditions are maintained despite changes to the internal and external environment

�Dynamic Equilibrium = condition that remains stable within fluctuating limits

Human Body Conditions

Some ranges are narrow; some more

broad

Examples�Blood pH (7.35 ± 0.2)�Body temperature (≈37°C ± 2°C)

Q. What other conditions are maintained at a constant level?

BRAINSTORM

(a) What is required for a building to maintain a constant temperature?

(b) Create a cycle that can work to maintain the temperature

Maintaining Homeostasis

Changing external/internal environment

�Exercise à increased heat production�Drink juice à blood glucose

Requires monitoring stimuli, feedback, and constant reaction via feedback mechanisms (2 types)

Feedback Mechanisms:

3 Parts

1. Sensor à detects changes in the environment and sends information to the integrator

2. Integrator à compares between existing and ideal conditions (set point) and orders the effector to take action if needed

3. Effector à the response; elements that act to return the system to optimal state

Feedback Mechanisms: 3 Parts

Negative Feedback

Loops

�Detects a stimulus, a change from the ideal conditions�Deviation in the internal/external

environment triggers a response to reverse the change�Maintains homeostasis

E.g.

Thermostat

Dueling Mechanisms

Antagonistic…or Opposite

effects!

�Thermoregulation à sweating vs. shivering

�Sugar levels à insulin (regulate) vs. glucagon (increase)

�Osmoregulation à hypotonic vs. hypertonic

Positive Feedback

Loops

�Increases the change�Usually a continuous increase in some internal variable�Away from homeostasis

E.g. Release of oxytocinduring childbirth àincreases contractions

SUMMARY

Key Point #1

�Homeostasis is state of the body where internal conditions are maintained at a level suitable for life processes; the tendency to resist change

SUMMARY

Key Point #2

�Negative feedback loops counteract changes of various properties from their set points; reduce change

SUMMARY

Key Point #3

�Positive feedback loops amplify their initiating stimuli, moving the system away from its starting state; increase change