Feedback
Mechanisms
WHAT IS FEEDBACK
MECHANISM?
Feedback Mechanism• mechanisms that regulate changes to
maintain a stable internal environment.
They have three steps
*1st Receptor- (such as a nerve when you are
touched or the cells of the pancreas that monitor
glucose level) detects change in the internal
environment.
*2nd Control Center- (such as the brain or an
organ), selects a response to the information from the
receptor.
*3rd Effector- (such as a muscle, gland, or an
organ) carries out the response to bring the body back
to homeostasis and this effect is detected by the
receptor, and the process starts again.
WHAT ARE THE TWO
FEEDBACK MECHANISMS?
NEGATIVE FEEDBACK
&
POSITIVE FEEDBACK
Negative feedback
systems – homeostasis
• Control of blood glucose
• Control blood calcium
• Control of body temperature
TEMPERATURE CONTROL
Temperature Control
CONTROL OF
TEMPERATURE
• Beckham sweats
b/c he is hot
(literally)  Sweat
evaporates,
removing heat 
Becks cools
down!
CONTROL OF
TEMPERATURE
• Cold means Becks is
losing heat 
shivers/ shakes to
generate heat  His
body goes through
cellular respiration to
convert sugar/fat
(like he has any) 
heat  blood is
diverted from skin 
Stops losing heat!
BLOOD SUGAR CONTROL
Blood Sugar Control
CONTROL OF BLOOD GLUCOSE
• High blood sugar levels long term cause
cell/organ damage
• Low blood sugar leads to fatigue, impaired
functioning, fainting, brain damage, etc.
• Negative feedback means that when
enough hormone is in the body, the
body stops producing the hormone
until it is needed again.
You eat. Glucose (sugar)
in the blood increases.
Increased glucose is detected by receptors
that notify the brain. It sends a message
to the pancreas to produce insulin.
Pancreas stops making insulin.
Blood glucose level drops as
it is removed by the cells.
Insulin tells muscle and liver to take up
glucose from the bloodstream and use it for energy
or store it for later. Brain reduces appetite.
• Knowing that:
– Insulin from the pancreas lowers blood
glucose by stimulating body cells to take
up glucose.
– Glucagon from the pancreas increases
blood sugar by stimulating the liver to
break down glycogen into glucose.
• Sketch a negative feedback loop that
controls blood sugar.
W
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What Happens?
• Between meals
Blood glucose lowPancreas secretes
glucagonLiver changes glycogen to
glucoseglucose sent to target tissues
• After a meal
Blood glucose highPancreas secretes
insulinGlucose goes to the Liver(Glygogen)
and goes to Target tissues
Diabetes
In the case shown in this picture, the body produces insulin but the target cells become
resistant and unresponsive to it. Diabetes can also be caused by the body not
producing enough insulin. The glucose does not enter the muscle and liver cells like it
should and it builds up in the blood causing complications.
Both People and Animals can
get Diabetes!
The obese
mouse on the
left does not
produce
enough leptin, a
hormone
produced by fat
cells.
Low body fat stimulates leptin production, which
stimulates appetite. The mouse is obese because
its low leptin levels give it an enormous appetite.
Leptin injections return the mouse’s weight to
normal. Humans sometimes have a leptin issue,
too, but the problem is a bad leptin receptor on
body cells. Alas, leptin injections won’t cure that.
BLOOD CALCIUM CONTROL
Blood Calcium
• Knowing the following:
– Calcitonin from the thyroid inhibits
calcium release from the bones.
– Parathyroid hormone stimulates release
of calcium from the bones.
• Sketch a negative feedback loop that
controls blood calcium level.
Positive Feedback
• Response to the stimulus is amplified
• i.e. you eat an appetizer, that makes you
more hungry so you eat more food
An example of positive
feedback is
childbirth
CHILD BIRTH
Ex: Birth
• Contractions start  More contractions
leads to more release of oxytocin 
Leads to more contractions (frequent
and stronger PUSH!
A negative feedback
system is one that tries to
keep the body constant.
In a positive feedback
system the change will
continue to increase in
one direction until
something happens in the
body to stop it.
• Given this patient profile, can you make
a diagnosis?
– Age – 14
– Gender – Male
– Exam: Normal weight, low blood pressure
– Lab tests: High blood glucose, low levels
of insulin.
• Now how about this patient?
– Age – 40
– Gender – Female
– Exam: Obese, high blood pressure
– Lab tests: High blood glucose, normal
levels of insulin.
3-2-1
Let the students list the following:
3 things that they’ve learned from the
lesson
2 interesting things
1 question they still have