A Quick Review
Modified from J.Pheifer
Auburn High School
 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.
….systems that receive information, react and
respond to maintain homeostasis
 Mechanism
that make adjustment to bring the
body back to an acceptable range (homeostasis)
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Coordinating centre
Monitor
Regulator
The thermostat as an example of homeostasis
 Primary

feedback system in the body:
Negative Feedback

Resists change
 Homeostasis
occurs with the help of:
Coordinating Center
 Monitors
 Regulators

 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.
 The
Brain
 Where the normal limits are set.
 Receives messages from monitors.
 Relays messages to the appropriate regulator.
 Organ(s)
of the body that respond to the
brain’s message to bring body back into
balance (homeostasis)
 Examples:

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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.
Maintaining
Homeostasis
Negative Feedback
System examples
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:

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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.
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.
