FEEDBACK MECHANISMS
& HOMEOSTASIS
HOMEOSTASIS
• Maintaining the internal environment
within a stable range given factors
that influence the external
environment
• Homeostasis controls many aspects
of the internal environment, for
example:
• Body temperature
• Blood concentrations of: glucose,
hormones, carbon dioxide and ions
• Oxygen levels
• Blood pH
• Blood pressure
• Solute concentration (Water balance)
FEEDBACK MECHANISMS
• Maintain homeostasis by detecting and responding
to a stimulus
• A non-biology example:
NEGATIVE FEEDBACK
• Reduces the size of
the stimulus to
restore homeostasis
• Temperature
regulation
• Blood glucose
• Blood pressure
• Stimulus effector response
NEGATIVE FEEDBACK: HUMANS
Protein receptor on cells
surface takes up insulin
BLOOD PRESSURE
NEGATIVE FEEDBACK
• A. stimulus – exercise
increases blood pressure
• B. receptor gets the
message to the (C)
control center.
• D. The effector, the heart,
pumps blood slower & E.
blood vessels dilate & get
wider to allow blood to
pass through).
• F. Homeostasis is
obtained
NEGATIVE FEEDBACK: PLANTS
POSITIVE FEEDBACK - CHILDBIRTH
POSITIVE FEEDBACK
• Response increases the
original stimulus to restore
homeostasis
• Rarely used
• Only normal when there is a
definite end point
• Childbirth
• Blood clotting