1. Homeostasis
A Quick Review
Modified from J.Pheifer
Auburn High School

2. What is Homeostasis?
The body’s ability to adjust to a fluctuating internal and external environment.
In homeostasis the body maintains balance, or steady state, despite environmental fluctuations.
Dynamic Equilibrium – the body is always in active balance.

3. Homeostatic systems are Feedback systems...
….systems that receive information, react and respond to maintain homeostasis

4. Negative Feedback System
Mechanism that make adjustment to bring the body back to an acceptable range (homeostasis)
Coordinating centre
Monitor
Regulator
The thermostat as an example of homeostasis

5. Homeostasis in the body
Primary feedback system in the body:
Negative Feedback
Resists change
Homeostasis occurs with the help of:
Coordinating Center
Monitors
Regulators

6. The Monitors... Special receptors found throughout the body.
Receptors are specialized – unique jobs
specific receptors that sense blood sugar levels; specific receptors that sense body temperature; and much more!!!
Receptors sense when limits are not at the normal limit/range.
Send message to coordinating center to alert of the imbalance.

7. The Coordinator center...
The Brain
Where the normal limits are set.
Receives messages from monitors.
Relays messages to the appropriate regulator.

8. The regulators...
Organ(s) of the body that respond to the brain’s message to bring body back into balance (homeostasis)
Examples:
The liver releases glucose to restore blood sugar levels.
Blood vessels constrict near skin to keep heat in the body, when internal temperature drops.
Skin emits sweat when hot, to reduce internal temperature.

9. Maintaining Homeostasis
Negative Feedback System examples

10. Positive feedback System
Moves the controlled variable even further away from a steady state (homeostasis)
Less common in the body.
Reinforces the change
A good example is the birth process:
Decrease in progesterone – initiate small contraction in the uterus
Contractions cause release of the hormone oxytocin. Oxytocin causes stronger contractions.
Baby moves towards cervix causing even more oxytocin to be released – continues until baby is expelled
Once expelled – uterine contractions stop – causing oxytocin to stop.

11. In summary…
Homeostasis refers to the body’s attempt to adjust to a fluctuating external environment.
All homeostatic control systems have three functional components: a monitor, a coordinating centre, and a regulator.
Negative feedback mechanisms trigger a response that reverses the changed condition.
Positive feedback systems move the controlled variable even further away from a steady state.