homeostasis final rashid

8/9/2019 Homeostasis Final Rashid

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IntroductionIntroduction

HomeostasisHomeostasis:: anyany selfself--regulatingregulating processprocess byby whichwhich

biologicalbiological systemssystems maintainmaintain stability,stability, whilewhile

adjustingadjusting toto conditionsconditions withwith dynamicdynamic responsesresponses thatthat

areare optimaloptimal forfor survivalsurvival.. IfIf homeostasishomeostasis isis

successful,successful, lifelife continuescontinues;; ifif unsuccessful,unsuccessful, disasterdisaster

oror deathdeath ensuresensures.. TheThe stabilitystability attainedattained isis actuallyactually aa

dynamicdynamic equilibrium,equilibrium, inin whichwhich continuouscontinuous changechange

occursoccurs yetyet relativelyrelatively uniformuniform conditionsconditions prevailprevail..

[[EncyclopediaEncyclopedia Britannica,Britannica, 20052005]]


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ObjectivesObjectives

DefineDefine homeostasishomeostasis..

EnlistEnlist homeostatichomeostatic factorsfactors..

DescribeDescribe feedbackfeedback systemssystems..

ExplainExplain temperature,temperature, bloodblood glucose,glucose, fluidfluid && electrolyteselectrolytes

andand acidacid--basebase balancebalance mechanismsmechanisms..

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What is Homeostasis?What is Homeostasis?

Homeostasis,Homeostasis, fromfrom thethe GreekGreek wordswords forfor "same""same" andand

"steady,""steady," refersrefers toto anyany processprocess thatthat livingliving thingsthings useuse totoactivelyactively maintainmaintain fairlyfairly stablestable conditionsconditions necessarynecessary forforsurvivalsurvival

The The abilityability oror tendencytendency ofof anan organismorganism oror cellcell totomaintainmaintain internalinternal equilibriumequilibrium byby adjustingadjusting itsitsphysiologicalphysiological processesprocesses..

The The AmericanAmerican HeritageHeritage DictionaryDictionary ofof thethe EnglishEnglish Language,Language, FourthFourth EditionEdition

CopyrightCopyright 20092009 bybyHoughtonHoughton MifflinMifflin CompanyCompany..

Maintenance of static or constant condition in the

internal environment of a cell.44


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Importance ofHomeostasisImportance ofHomeostasis

HomeostasisHomeostasis keepskeeps thethe bodybody environmentenvironment underunder

controlcontrol andand keepskeeps thethe conditionsconditions rightright forfor cellscells toto livelive

andand functionfunction..

ForFor ee..gg.. EnzymesEnzymes inin ourour bodybody cancan onlyonly workwork atat aa

narrownarrow rangerange ofof pHpH andand temperaturetemperature.. ChangesChanges inin thesethese

conditionsconditions cancan leadlead toto enzymeenzyme denaturationdenaturation ororinactivationinactivation thatthat cancan subsequentlysubsequently affectaffect thethe workingsworkings

ofof ourour bodybody..


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FactorsFactors within the internal environment mustwithin the internal environment must

be keptbe kept constantconstant

TemperatureTemperature (thermoregulation)(thermoregulation)

TheThe concentrationconcentration ofof glucoseglucose

TheThe concentrationconcentration ofof ions,ions, ee..gg.. sodiumsodium andand potassiumpotassium The The osmoticosmotic pressure,pressure, determineddetermined byby thethe relativerelative

concentrationsconcentrations ofof waterwater andand solutessolutes (osmoregulation)(osmoregulation)

TheThe pHpH (acid(acid--basebase balancebalance))

TheThe concentrationconcentration ofof carboncarbon dioxidedioxide

NitrogenousNitrogenous wastewaste productsproducts andand otherother toxictoxic substances,substances,

whichwhich areare eithereither eliminatedeliminated oror atat leastleast keptkept toto aa minimumminimum66


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FoFor any homeostatic control tooccurr any homeostatic control tooccurthere must be:there must be:

AA stimulusstimulus whichwhich isis aa changechange inin thethe internalinternal

environmentenvironment..

AA receptorreceptor whichwhich cancan detectdetect thethe stimulusstimulus..

An An automaticautomatic oror selfself--regulatoryregulatory correctivecorrective

mechanismmechanism toto finallyfinally bringbring aboutabout

AA negativenegative feedbackfeedback..77


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3 componentsin homeostatic control mechanism

1. Receptors

3. Effectors

Detect

changes

2. Control

centre

Define

changes

Execute the

changes

Triggers appropriate

corrective actions

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HomeostasisHomeostasis

is achieved by:is achieved by:

Negative feedbackNegative feedback


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Negative feedbackNegative feedback

For example,For example,

IfIf thethe humanhuman hypothalamushypothalamus detectsdetects aa highhigh bloodblood

temperaturetemperature itit sendsend nervenerve impulsesimpulses toto sweatsweat glands,glands, whichwhich

increaseincrease sweatsweat outputoutput andand causecause evaporativeevaporative coolingcooling..

WhenWhen thethe bodybody temperaturetemperature returnsreturns toto normal,normal, nonoadditionaladditional signalssignals areare sentsent..

Receptors (Hypothalamus, skin) > Control center (Hypothalamus) > Effectors

(muscles/sweat glands/BV)

mechanism consists of reducing the output or activity of any

organ or system back to its normal range of functioning.

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PositivePositive feedbackfeedback MechanismsMechanisms areare designeddesigned toto accelerateaccelerate oror enhanceenhance thethe outputoutput

createdcreated byby aa stimulusstimulus thatthat hashas alreadyalready beenbeen activatedactivated..

pushespushes changeschanges furtherfurther inin thethe samesame way,way, strengthenstrengthenoror reinforcereinforceaachangechange inin thethe bodysbodys controlledcontrolled conditionsconditions

For example :Uterine contractionDuring childbirth, the babys head press against receptors near the openingof the uterus,

stimulates uterine contractions which cause greater pressure against theuterine opening, heightening the contraction, which causes still greater

pressure.

Positive feedback brings childbirth to completion.

Receptors (stretch-sensitive nerve cell in cervix) > Control center (brain, release

oxytocin) > Effectors (muscles in wall of uterus contract more forcefully)1212


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Negative FeedbackNegative Feedback

HomeostasisHomeostasis involvesinvolves anan importantimportant principleprinciplecalledcalled negativenegative feedbackfeedbackwhichwhich isis thethe reversereverseeffecteffect ofofaa stimulusstimulus..

An An increaseincrease inin temperaturetemperature will will induceinduce aafeedbackfeedback toto decreasedecrease thethe temperaturetemperature..

AA decreasedecrease inin temperaturetemperature willwill induceinduce aa feedbackfeedbacktoto increaseincrease thethe temperaturetemperature..

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ThermoregulationThermoregulation

InIn humans,humans, bodybody temperaturetemperature isis controlledcontrolled bybythethe thermoregulatorythermoregulatory centrecentre:: HypothalamusHypothalamus

HypothalamusHypothalamus receivesreceives inputinput fromfrom twotwo setssets ofof

receptorsreceptors:: ReceptorsReceptors inin thethe hypothalamushypothalamus (monitor(monitor thethe

temperaturetemperature ofof thethe bloodblood asas itit passespasses throughthrough thethe

brain)brain).. ReceptorsReceptors inin thethe skinskin (monitor(monitor thethe externalexternal

temperaturetemperature))..

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ThermoregulationThermoregulation

WhenWhen bodybody temperaturetemperature risesrises,, TheThe erectorerector musclesmuscles relax,relax, hairshairs lielie flatflat againstagainst thethe skin,skin,

nono longerlonger trappingtrapping air,air, allowingallowing moremore heatheat toto bebe lostlost

byby radiationradiation..

(radiation(radiation:: heatheat transfertransfer fromfrom bodybody toto air)air)

TheThe dermaldermal bloodblood vesselsvessels dilatedilate andand thethe sweatsweat glandsglands

areare stimulatedstimulated intointo vigorousvigorous secretorysecretory activityactivity..

EvaporationEvaporation ofof sweatsweat fromfrom skinskin surfacesurface dissipatesdissipatesbodybody heatheat andand coolscools thethe body,body, thusthus preventingpreventing

overheatingoverheating..

Heat transfer from the body to the surroundings, evaporative cooling1616


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When the external environment is coldWhen the external environment is cold,,

ImpulsesImpulses toto thethe erectorerector musclemuscle attachedattached toto youryour hairhair folliclesfollicles

contract,contract, whichwhich mademade youryour hairshairs stand,stand, trappingtrapping airair..

dermaldermal bloodblood vesselsvessels constrictedconstricted.. ThisThis causescauses thethe warmwarm bloodblood

toto bypassbypass thethe skinskin temporarilytemporarily andand allowsallows skinskin temperaturetemperature totodropdrop toto thatthat ofof thethe externalexternal environmentenvironment..

ShiveringShivering:: involuntaryinvoluntary shudderingshuddering contractionscontractions ofof thethe skeletalskeletal

muscles,muscles, effectiveeffective inin increasingincreasing bodybody temperature,temperature, musclemuscle

activityactivity producesproduces largelarge amountsamounts ofof heatheat..

EnhanceEnhance thyroxinethyroxine (thyroid(thyroid gland)gland) andand adrenalineadrenaline (adrenal(adrenal

gland)gland) releaserelease:: increasesincreases thethe metabolicmetabolic raterate..1717


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(a) Erectormuscle contract (b) Erectormuscle relax

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VasodilationVasodilation and vasoconstrictionand vasoconstriction

VasodilationVasodilation ofof cutaneouscutaneous bloodblood vesselsvessels BloodBlood flowflow inin thethe skinskin increases,increases, facilitatingfacilitating heatheat lossloss..

VasoconstrictionVasoconstriction ofof cutaneouscutaneous blood vesselsblood vessels

Blood flow in the skin decreases, lowering heat loss.Blood flow in the skin decreases, lowering heat loss. Blood is restricted to deep body areas and largely bypasses theBlood is restricted to deep body areas and largely bypasses the

skin.skin.

The skin is separated from deeper organs by a layer of insulatingThe skin is separated from deeper organs by a layer of insulatingsubcutaneous (fatty) tissue, heat loss reduced.subcutaneous (fatty) tissue, heat loss reduced.

Restriction blood flow to the skin for a brief period is not a problem, but if prolonged exposure to very cold weather, skin cells deprivedof oxygen and nutrients begin to die. This extremely serious

condition is called frostbite.1919


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Regulation ofblood temperatureRegulation ofblood temperature

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In humans, theIn humans, thehypothalamushypothalamus

Contains a group of nerveContains a group of nerve

cells that function ascells that function asaa thermostatthermostat

Thermostat inhypothalamus

activatescooling

mechanisms.

Sweat glandssecrete

sweat that evaporates,

cooling the body.

Bloodvessels

in skin dilate:capillaries fill

withwarm blood;

heat radiates from

skin surface.

Body temperature

decreases;

thermostat

shutsoffcoolingmechanisms.

Increased body

temperature (suchas

when exercising

orin hot surroundings)

Homeostasis:

Internal body temperature

3638rC

Body temperature

increases;

thermostat

shutsoffwarming

mechanisms.

Decreased body

temperature

(cold

surroundings)

Bloodvesselsin

skin constrict,diverting blood

fromskin todeeper tissuesand reducing

heat loss

fromskin

surface.

Skeletalmuscles rapidly

contract,causing shivering,

which generatesheat.

Thermostat in

hypothalamus

activates

warming

mechanisms.

Figure

The thermostat function of

thehypothalamusin

human thermoregulation

*

*

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Mechanismofbody temperatureMechanismofbody temperature

HeatHeat--loss mechanismsloss mechanisms Skin hairs loweredSkin hairs lowered VasodilationVasodilation ofof cutaneouscutaneous blood vesselsblood vessels

(skin arterioles dilate)(skin arterioles dilate)

Enhanced sweatingEnhanced sweating

HeatHeat--promoting mechanismspromoting mechanisms Skin hair raised, trapping airSkin hair raised, trapping air Vasoconstriction ofVasoconstriction of cutaneouscutaneous blood vesselsblood vessels

(skin arterioles constrict)(skin arterioles constrict) ShiveringShivering

Glands secretingGlands secreting adrenaline andadrenaline and thyroxinethyroxine

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Blood glucose homeostasisBlood glucose homeostasis

Glucose is a major fuel for cellsGlucose is a major fuel for cells

Its metabolism, regulated by hormone actionIts metabolism, regulated by hormone action

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Regulation ofblood glucoseRegulation ofblood glucose concentrationconcentration

Body Body cellscells needneed glucoseglucose forfor tissuetissue respirationrespiration toto

provideprovide energyenergy.. TheThe concentrationconcentration inin bloodblood plasmaplasma

remainsremains relativelyrelatively constantconstant..

GlucoseGlucose levellevel maymay riserise afterafter aa mealmeal.. ItIt fallsfalls duringduring

exerciseexercise oror starvationstarvation..

HowHow isis thethe concentrationconcentration ofof glucoseglucose inin bloodblood

plasmaplasma regulated?regulated?

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GlucoseGlucose regulationregulation

Figure

STIMULUS:

Blood glucoselevel rises

after eating.

Homeostasis:

Blood glucose level90 mg/100 mL

STIMULUS:

Blood glucose

level drops

below set point.

1 When blood glucose

level rises, the pancreas

secretes insulin, ahormone, into the blood.

Glucagon promotes

the breakdown of

glycogen in theliver and the

release of glucose

into the blood,

increasing blood

glucose level.

4

When blood glucose

level drops, the pancreas

secretes the hormone

glucagon into the blood.

3

Insulin enhances the

uptake of glucose in body

cells and stimulates the liver

andmusclecells to store

glucose as glycogen. As a

result, blood glucose level

drops.

2

Hyperglycemic

Hypoglycemic

F-cells

E-cells2525


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Control ofblood glucose concentrationControl ofblood glucose concentration

INSULININSULIN

A hormone produced by theA hormone produced by theFF cellscells of the islets ofof the islets ofLangerhansLangerhans in the pancreas.in the pancreas.

Secretion is stimulated by theSecretion is stimulated by theriserise in blood glucose.in blood glucose.

Speeds up the rate at whichSpeeds up the rate at which

glucose is taken into liver andglucose is taken into liver andmuscle cells from the blood,muscle cells from the blood,stored asstored as glycogenglycogen..

GLUCAGONGLUCAGON

A hormone produced by theA hormone produced by theEE cellscells of the islets ofof the islets ofLangerhansLangerhans in the pancreas.in the pancreas.

Secretion is stimulated by theSecretion is stimulated by thefallfall in blood glucose.in blood glucose.

breakdown of glycogen in thebreakdown of glycogen in the

liver.liver.

Stimulates the formation ofStimulates the formation ofglucose from other moleculesglucose from other moleculessuch as amino acids.such as amino acids.

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THREE sources ofblood glucoseTHREE sources ofblood glucose

DigestionDigestion ofof carbohydratescarbohydrates inin thethe dietdiet

BreakdownBreakdown ofof glycogenglycogen ((glycogenesisglycogenesis))

ConversionConversion ofof nonnon--carbohydratecarbohydrate compoundscompounds

((gluconeogenesisgluconeogenesis))

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Blood water homeostasis (Osmoregulation)Blood water homeostasis (Osmoregulation)

Homeostasis of blood volume and osmolality

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Blood water homeostasis (Osmoregulation)Blood water homeostasis (Osmoregulation)

TheThe waterwater potentialpotential ofof thethe bloodblood mustmust bebe regulatedregulated totopreventprevent lossloss oror gaingain ofof waterwater fromfrom cellscells..

OsmoregulationOsmoregulation

RegulatesRegulates solutesolute concentrationsconcentrations andand balancesbalances thethe gaingain andand losslossofof waterwater

OsmoregulationOsmoregulation isis basedbased largelylargely onon controlledcontrolled movementmovementofof solutessolutes

BetweenBetween internalinternal fluidsfluids andand thethe externalexternal environmentenvironment

BloodBlood waterwater homeostasishomeostasis isis controlledcontrolled bybyhypothalamushypothalamus,,whichwhich containscontains osmoreceptorosmoreceptor cellscells,, detectdetect changeschanges inin thethe

waterwater potentialpotential ofof thethe bloodblood passingpassing throughthrough thethe brainbrain..3232


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Osmoreceptors

in hypothalamus

Drinking reducesbloodosmolarity

toset point

H2O reabsorption

helpsprevent further

osmolarity

increase

STIMULUS:

The releaseof ADH is

triggeredwhen osmo-

receptorcellsin the

hypothalamusdetect an

increasein theosmolarity

of the blood

Homeostasis:

Bloodosmolarity

Hypothalamus

ADH

Pituitary

gland

Increased

permeability

Thirst

Collecting duct

Distaltubule

Figure

Antidiuretic hormone

(ADH) enhances fluid

retention by making the

kidneys reclaim more

water

When body becomesdehydrated,

the osmotic [ c ] of

the blood o

Posterior lobe of thepituitary glandADH

1

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Low blood waterpotentialLow blood waterpotential ((too littletoo little water)water)

HypothalamusHypothalamus controlscontrols thethe sensationsensation ofof thirstthirst andand itit alsoalso secretessecretes

thethe hormonehormone ADHADH ((antidiureticantidiuretic hormonehormone;; aa..kk..aa vasopressin)vasopressin)..

ADHADH isis storedstored inin pituitarypituitary glandgland,,

andand itsits targettarget cellscells areare thethe distaldistal tubulestubules andand collectingcollecting ductsducts ofof thethe kidneykidney

nephronsnephrons..

ADHADH increasesincreases thethe permeabilitypermeabilityofof thethe epitheliumepithelium toto waterwater..

IncreasedIncreased waterwater reabsorptionreabsorption,, reducesreduces urineurine volumevolume..3535


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OsmolarityOsmolarity ofof thethe bloodblood subside,subside,

reducesreduces thethe activityactivity ofof osmoreceptorosmoreceptor cellscells inin thethe

hypothalamushypothalamus

andand lessless ADHADH isis secretedsecreted

Conti

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LowLow blood waterpotentialblood waterpotential

(lowosmotic concentration)(lowosmotic concentration) > low blood pressure> low blood pressure

A A secondsecond regulatoryregulatory mechanismmechanism involvesinvolves

juxtaglomerularjuxtaglomerular apparatusapparatus (JGA),(JGA), locatedlocated nearnear thethe

afferentafferent arteriolearteriole thatthat suppliessupplies bloodblood toto thethe glomerulusglomerulus..

WhenWhen thethe bloodblood pressure/bloodpressure/blood volumevolume inin thethe afferentafferent

arteriolearteriole drops,drops, enzymeenzyme reninrenin initiatesinitiates thethe conversionconversion ofofangiotensinogenangiotensinogen (a(a plasmaplasma protein)protein) toto angiotensinangiotensin IIII (a(a

peptide)peptide)..

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The renin-angiotensin-aldosterone system (RAAS)

Atrial Natriuretic Peptide (ANP)

Are part of a complex feedback circuit that functionsin homeostasis

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Aldosterone

Increase retention of

Na+ by the kidneys,greater fluid retention,increases blood vol.

Angiotensin II

Vasoconstriction,increase blood pressure

Renin Angiotensinogen(plasma protein)

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Renin-Angiotensin-AldosteroneSystem


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