Homeostasis

1. Maintenance of a stable internal environment is called homeostasis. 

2. Homeostasis is regulated through control systems, which have receptors, a set point and effectors in common. Examples include: 

a. Homeostatic mechanisms regulate body temperature in a manner similar to the functioning of a home heating thermostat.  

b. Another homeostatic mechanism employs pressure receptors to regulate blood pressure.

3. Most of the body’s homeostatic controls involve negative feedback mechanisms because of the increased control with negative feedback. However there are a few examples of positive feed back systems.  These systems operate for short periods of time. 

• Childbirth is an example of positive feedback. 
• Positive feedback loops amplify the original stimulus moving further from equilibrium.
• Inflammation from a sprained ankle.  Tissue damage causes significant amounts of swelling for protection.

4. Each individual uses homeostatic mechanisms to keep body levels within a normal range; normal ranges can vary from one individual to the next. 

    What does negative feedback mean?  ________________________________________

    What does a negative feedback system allow? _____________________________________

    What would happen if you tried to use positive feedback for temperature control? ____________________________

     Why doesn’t the body use positive feed back very often?