Uploaded by Jesse Bowcock

L1 Homeostasis

Maintaining the internal environment
Homeostasis is the state of steady
internal physical and chemical conditions maintained
by living systems, despite changes in the external
• Some simple examples of homeostasis: When it is cold you
shiver, when it is hot you sweat to maintain the optimum
body temperature of 37.5 degrees Celsius.
• There are a number of different body systems that work
together to maintain the balance across the entire organism.
• In order to keep internal
conditions (eg.
Temperature or nutrient
concentration) stable,
organisms must have a
feedback mechanism to
quickly identify and
control all changes to
• Draw a diagram of the
stimulus response in
your notes
Negative Feedback
• Mechanisms that counteract the stimulus are referred to
as Negative Feedback.
• An example is temperature, when your core body
temperature increases the body will counteract the
increase by activating sweat glands throughout the body.
Negative Feedback
• This process can be compared to the air conditioning
systems you see so often in homes and offices.
• There is a sensor (thermometer) in an air conditioner you
input the desired temperature and the control centre
(computer) in the air con will send info to the effector, to
release cold air.
Negative Feedback
Negative Feedback
Conditions in the body are constantly fluctuating, negative feedback
is constantly working to maintain the internal environment.
The figure below shows how homeostasis operates to continually
readjust body conditions to maintain them within tolerance limits.
Complete Biozone worksheet p175, 178, 179