-

1. HomeostasisHomeostasis
Negative feedback systems in theNegative feedback systems in the
human bodyhuman body

2. .
What is homeostasis?What is homeostasis?
 Process that occurs in allProcess that occurs in all
living thingsliving things
 All organ systems workAll organ systems work
together to achievetogether to achieve
homeostasishomeostasis
 Ability of an organism toAbility of an organism to
maintain its internalmaintain its internal
environment, despiteenvironment, despite
changes to its internal orchanges to its internal or
external environmentexternal environment
http://en.wikipedia.org/wiki/File:Tightrope_artist_Cologne_1.jpg

3. How does homeostasis work?How does homeostasis work?
 Feedback pathwaysFeedback pathways
 A cellular relay race!A cellular relay race!
 Specific organs andSpecific organs and
structures muststructures must
communicate with eachcommunicate with each
other in response toother in response to
changes in the bodychanges in the body
 Keeps levels of certainKeeps levels of certain
processes within aprocesses within a
normal rangenormal range
http://en.wikipedia.org/wiki/File:Southern_12_stage-02_1988.jpg

4. What things in your body need to beWhat things in your body need to be
kept within a range?kept within a range?
 Body TemperatureBody Temperature
 Blood pressureBlood pressure
 Blood pHBlood pH
 OO22 and COand CO22 concentrationconcentration
 Osmoregulation-Water balanceOsmoregulation-Water balance
 Blood glucoseBlood glucose

5. Cellular Relay RaceCellular Relay Race
 StimulusStimulus
 ReceptorReceptor
 IntegratingIntegrating
centercenter
 EffectorEffector
 ResponseResponse
 Reverses theReverses the
stimulusstimulus

6. Negative Feedback PathwaysNegative Feedback Pathways
 Way in which mostWay in which most
homeostatichomeostatic
mechanisms workmechanisms work
 The product of theThe product of the
pathway inhibits, orpathway inhibits, or
shuts down, theshuts down, the
original signaloriginal signal
 Why is this anWhy is this an
important feature inimportant feature in
living things?living things?

7. Life Sciences-HHMI Outreach.
Copyright 2009 President and Fellows
of Harvard College.
Why is feedback important inWhy is feedback important in
living things?living things?
 Allows baseline to beAllows baseline to be
regainedregained
 Conserves resourcesConserves resources
 Cellular MaterialsCellular Materials
 Energy (ATP)Energy (ATP)

8. mouth
Stomach
Sm. Intestine
Pancreas
ß-cells
Target cells-
Muscle
Target cells-
Liver
Target cells-
Brain
Circulatory Runners
Game set-up
http://commons.wikimedia.org/wiki/File:Pictgram_running_man.svg
http://en.wikipedia.org/wiki/File:Archery_Target_80cm.svg
http://en.wikipedia.org/wiki/File:Llave_bronce.jpg
http://commons.wikimedia.org/wiki/File:Day-template.svg
http://commons.wikimedia.org/wiki/File:Icon_announcer.svg
Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College.

9. mouth
Stomach
Sm. Intestine
Pancreas
ß-cells
Target cells-
Muscle
Target cells-
Liver
Target cells-
Brain
Circulatory Runners
“Glucose!! Release the insulin!”
Lots of glucose
circulating, so
Pancreas calls out
for insulin
.

10. mouth
Stomach
Sm. Intestine
Pancreas
ß-cells
Target cells-
Muscle
Target cells-
Liver
Target cells-
Brain
Circulatory Runners
“Glucose!! Release the insulin!”
Insulin has been
passed to the target
cells. Targets can
now receive
glucose.
http://commons.wikimedia.org/wiki/File:Pictgram_running_man.svg
http://en.wikipedia.org/wiki/File:Archery_Target_80cm.svg
http://en.wikipedia.org/wiki/File:Llave_bronce.jpg
http://commons.wikimedia.org/wiki/File:Day-template.svg
http://commons.wikimedia.org/wiki/File:Icon_announcer.svg
Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College.

11. mouth
Stomach
Sm. Intestine
Pancreas
ß-cells
Target cells-
Muscle
Target cells-
Liver
Target cells-
Brain
Circulatory Runners
“Hold insulin production”
Pancreas stops
insulin from being
passed once
there is no more
glucose
circulating

12. Dueling HormonesDueling Hormones
What goes up, must come down!What goes up, must come down!
InsulinInsulin
 Produced byProduced by ββ-cells-cells
of the Pancreasof the Pancreas
 Released intoReleased into
circulatory systemcirculatory system
when blood glucose iswhen blood glucose is
highhigh
 Facilitates theFacilitates the
transport of glucosetransport of glucose
into target cellsinto target cells
GlucagonGlucagon
 Produced byProduced by αα-cells-cells
of the pancreasof the pancreas
 Released into theReleased into the
circulatory systemcirculatory system
when blood glucose iswhen blood glucose is
lowlow
 Signals the liver toSignals the liver to
break down glycogenbreak down glycogen
into simple glucoseinto simple glucose

13. Dueling MechanismsDueling Mechanisms
What goes up, must come down!What goes up, must come down!
ThermoregulationThermoregulation
Sweating (cooling) vs. shivering (warming)Sweating (cooling) vs. shivering (warming)
Blood PressureBlood Pressure
Vasconstriction vs. vasodilationVasconstriction vs. vasodilation
OsmoregulationOsmoregulation
Hypotonic vs. hypertonicHypotonic vs. hypertonic

14. Food for thought…Food for thought…
 On average, how many organ systems areOn average, how many organ systems are
involved in each of the processes we’veinvolved in each of the processes we’ve
explored?explored?
 Are there any organ systems that you see inAre there any organ systems that you see in
allall of these processes?of these processes?
 What might happen to these pathways if justWhat might happen to these pathways if just
oneone system was not functioning properly?system was not functioning properly?