Homeostasis
Standard 4 Key idea 1
Major understanding 1.2d and
1.2 e
Bell ringer question
• How does your body react when it is too
hot?
• How does your body react when it is too
cold?
Homeostasis
• Homeostasis: balance, steady state.
Human body systems work to maintain a
balance, homeostasis. (Your body wants
to stay the same.)
http://fiveyearhealthplan.wordpress.com/homeostasis/
Video
• http://www.youtube.com/watch?v=ZQLru
oTRGVk
• Fill out the handout that has questions
about the video.
Examples of mechanism to
maintain homeostasis
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Carbon dioxide level in the body tissues
Body temperature
Glucose level in the blood
Water level
Salt level
Blood pressure level
Negative feedback
• A change in some condition causes a
response that counteracts or reverses the
changed condition. i.e. how the body
temperature is maintained.
https://en.wikipedia.org/wiki/Feedback
Examples of negative feedback
Regulation of room temperature
1. Change (door opens, letting cold air in)
2. Room temperature decreases below set point.
3. Thermometer (sensor) detects the change and signals
thermostat (a device that switches on and off the
furnace or air conditioner).
4. The furnace increases heat.
5. Room temperature increases to set point.
Solomon, Berg, and Martin. (2008). Biology. Belmont, CA: Thomson Higher Education.
http://www.revisescience.co.uk/2011/schools/otheraqaw/abhomeostasis.asp
Human body temperature
regulation
1. Change (cold wind)
2. Body temperature decreases below set point
(37 ºC).
3. Nerve cells (sensors) detect change.
4. Nerve cells signal the brain.
5. The brain activates homeostasis mechanisms
(muscles shiver, no sweats, etc)
6. Body temperature increases to the set point
(37 ºC).
Homeostasis and disease
• If there is a disruption in any human
system, there may be corresponding
imbalance in homeostasis. If imbalance
in homeostasis continues, it can cause a
disease.
Example of diseases caused by
imbalance in homeostasis
• Type 2 diabetes: too much blood sugar in the
blood  too much insulin to maintain
homeostasis at some point, insulin will not
be produced any more.
As a result, blood glucose
level will not be maintained,
causing serious side effects.
http://durhamdiabetescoalition.org/information/type-2-diabetes
Exit question
• Define homeostasis in your own words.
• Give three examples of homeostasis in
the human body.