Download Homeostasis: A Balancing Act Lab

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BiologyLab:HomeostasisandExercise
Background:
Homeostasis(Greekfor“stayingthesame”)isaprocessbywhichthebodymaintainsastableinternalenvironment.
Thehypothalamusisapartofthebrainthathelpsthebodymaintainhomeostasis.Itislocatedinthebrainjustabove
thebrainstemandisagroupofneuronsthatformstheprimarylinkbetweenthenervoussystemandtheendocrine
system.Thissmallpartofthebrainisresponsibleforregulatingmanykeybody
processesincludinginternalbodytemperature,hunger,thirst,bloodpressure,and
daily(circadian)rhythms.
Mostbodysystemsmaintainhomeostasisbyusingpositiveornegativefeedback
mechanisms.Whenthebrainreceivesmessagesfromthebodyaboutaninternal
changeinoneofitssystems,itworkstorestorethesystemtoitsnormalstate.
Negativefeedbackmechanismsarefoundintheregulationofbloodpressure,
heartrate,andinternaltemperaturecontrols.Forexample,thenormalinternal
temperatureforthehumanbodyisapproximately98.6°F.Ifthebodytemperature
risesbecauseofexercise,thebodywillstarttotryandcoolitselfoff.Thishappensthroughcoordinationbetweenthe
hypothalamusandthevariousbodysystemsthatareaffected.Signalsaresentthatallowbloodvesselstoreturntothe
normalstate,sweattobeproduced,porestobedilated,andheartandbreathingratetonormalize.Thisisverysimilar
tothewayathermostatworks.Whenthetemperatureofaroombecomestoowarm,thethermostatwillswitchonthe
airconditioningandcooltheroom.Whentheroomtemperaturereachesasetdesiredtemperature,thesystemturns
off.
Bodysystemsworktomaintainhomeostasisinwayswearenotevenawareof.Forexample,thebodyisconstantly
workingtomaintainanormalglucoselevelinyourblood.Whenyoueatsomethingthatcontainsalotofsugar,the
glucoseconcentrationinyourbodyrisesabovenormal.Whenglucoselevelsaretoohigh,thebodyreleasesahormone
calledinsulinwhichstimulatestheabsorptionofglucosebythepancreastohelpreturnthebloodsugarleveltonormal.
Positivefeedbackisamechanismthatismuchrarerinahealthybody.Insteadofrestoringthebodytoanormalstate,
thepositivefeedbackmechanismcausesanevengreaterchange.Anexampleofpositivefeedbackcanbefoundinthe
releaseofoxytocin,ahormonethatintensifiesthecontractionsthattakeplaceduringchildbirth.Asthebaby’sheadis
readytomoveoutofthemother’sbody,oxytocinincreasesandthelevelsofcontractionsincreasethuspushingthe
babyout.Inthisinstance,thebodyrespondstoaneventwithmore“force”orinastrongerway.
Problem:
Howdoesexerciseaffectaperson's heart rate,breathing rate,andperspiration level?
Hypothesis:
Writeahypothesisabouttheeffectofexerciseontherespondingvariables.Usethe“If…, then…, because…”
statement.(READ the procedure first, to gain a better understanding before writing your hypothesis)
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Materials:
You,plustwoothergroupmember(groupsof3)
Aclock(youmayuseyourphone)
Procedure:
1. Chooseonevolunteertocompletejumpingjacksatapacethatcanbemaintainedforeightminutes.Makesure
thevolunteerisinactiveforatwominutesbeforetheexperimentbegins.
2. Measuretheheartratebytakinghisorherpulse;youcandothisoneoftwoways.(1)RadialPulse:Thisisprobably
whatwe'remostfamiliarwithwhenvisitingthedoctor'soffice.Taketwofingers,preferablythe2ndand3rdfinger,and
placetheminthegrooveinthewristthatliesbeneaththethumb.Moveyourfingersbackandforthgentlyuntilyoucan
feelaslightpulsation-thisisthepulseoftheradialarterywhichdeliversbloodtothehand.Don'tpresstoohard,or
elseyou'lljustfeelthebloodflowingthroughyourfingers!(2)CarotidPulse:Thecarotidarteriessupplybloodtothe
headandneck.Youcanfeelthepulseofthecommoncarotidarterybytakingthesametwofingersandrunningthem
alongsidetheouteredgeofyourtrachea(windpipe).Thispulsemaybeeasiertofindthantheradialartery.Sincethe
carotidarteriessupplyalotofthebloodtothebrain,it'simportantnottopressonbothofthematthesametime!
Countthenumberofbeatsin15seconds.Yourpartnerwillusetheclockorstopwatchtotellyouwhentostartand
whentostop.
3. Multiplythenumberofbeatsin15secondsby4tocalculatethebeatsperminute.
RecordthedataintheTable1underthe0minutesbox.
#ofbeatsX4=beatsperminute
4. Measuretheperson'sbreathingratebycountingthenumberofbreathstakenin15seconds.Themultiplythis
numberby4tocalculatebreathsperminute.Addthisinformationtothetable.
#ofbreathsX4=breathsperminute
5. Ratetheperson'sperspirationlevelfrom1to5(1=none;5=dropletsdrippingdowntheface).Recordthis
observationinthetable.
6. Havethevolunteerdojumpingjacksfor2minutes.After2minutes,measureheartrate,breathingrate,and
perspirationlevel(refertoSteps2through5),andrecordthedata.Measurethepulse,breathingandperspirationlevels
asquicklyasyoucansothatthevolunteercanresumeexercise.Donothavevolunteerwaitwhileyoudothe
calculationsandenterthedata.
7. RepeatStep6threemoretimesandrecordyourdataateachpoint.(4min,6min,8min)
8. Afterthefinalrecording,wait1minuteand30secondswiththevolunteeratcompleterest.Thenmeasurethe
pulse,breathingandperspirationlevelsagain.Recordthisdataunderthe“9.5Time(min.)box”.
TABLE1.EFFECTSOFEXERCISE
Time(min.)
HeartRate
(beats/min.)
BreathingRate
(breaths/min.)
PerspirationLevel
0
2
4
6
8
9.5
AnalyzeandConclude:
1. Whatisthemanipulatedvariableinthisexperiment?
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2a.Graphtherelationshipbetweenthemanipulatedandrespondingvariables.Createonegraphtodisplayallofyour
data.
2b.Explainwhyyouthinkitwouldbeimportanttographall3respondingvariablesononegraph.
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3. Whataretheeffectsofexerciseovertimeonthecirculatoryandrespiratorysystems?Onperspirationlevel?
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4. Whatotherprocessescouldyouhavemeasuredtodeterminetheexternalandinternaleffectsofexerciseonthe
body? List at least 3.
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5. Howisperspirationlevelrelatedtobodytemperature?Howisperspirationrelatedtohomeostasis?
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6. Howisanegativefeedbackmechanismbeingrepresentedinthislab?
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