Introduction to Animal PhysiologyHomeostasis

PhysiologyThe study of the functions of living organismswhole organismsorgan systemsorganstissuescells

Physiologygroups of cells with similar characteristics or specializations form tissuesdifferent tissues combine to form organsdiscrete structures with specific functionsorgans which function together form organ systems

Physiologytissues occur in four basic typesepithelial tissues form linings or coveringsperform functions appropriate to organconnective tissues exist in a matrixsupport and reinforce other tissuesmuscle tissues contractprovide movement or propulsionnervous tissues transmit and process information

tissues of the stomach wallFigure 41.2

Table 41.1

Homeostasismost organ systems contribute to homeostasismaintenance of a constant internal environment in spite of constant changeprovides for material needs of cellsremoves wastes from cellsregulates physical environment of cellscommunicates among cells

homeostasis in a cellular suitcaseFigure 41.1

Homeostasishomeostatic regulatory componentscontrolled systems - effectorsregulatory systemsacquire informationprocess informationintegrate informationsend commands

Homeostasishomeostatic regulatory variablessetpointoptimal chemical or physical conditionfeedback informationactual current conditionerror signaldiscrepancy between setpoint and feedback value

Homeostasishomeostatic regulatory inputsnegative feedbackreduces or reverses activity of effectorreturns condition to set pointpositive feedbackamplifies activity of effectorself-limiting activitiesfeedforward informationchanges setpoint

the responsible driver exampleFigure 41.4

Homeostasis: thermoregulationliving cells cannot survive temperatures above or below fairly narrow limitsthermosensitivities of organisms varythermosensitivities of effectors vary

Q10 quantifies temperature sensitivityratio of physiological rate at one temperature to the rate at 10C lower temperatureQ10 = RT / RT-10

Figure 41.5biological range of Q10values

Homeostasis: thermoregulationacclimatization can alter an animals temperature responsechanges that allow optimal activity under different climatic conditions [e.g. seasonal temperature variation]metabolic compensation maintains metabolic rate in different seasonsaccomplished with alternate enzyme systems (e.g.)

acclimatization may include metabolic compensationFigure 41.6

Homeostasis: thermoregulationanimals are classified by how they respond to environmental temperatureshomeothermmaintains a constant body temperature as ambient temperature changespoikilothermchanges body temperature as ambient temperature changes

Homeostasis: thermoregulationanimals are classified by how they respond to environmental temperaturesandtheir sources (sinks) of body heatectothermexternal heat sources/sinksendothermactive heat generation and cooling

ectotherms and endotherms utilize different sources of body heatFigure 41.7

behavioral temperature regulation in an ectothermFigure 41.8

Homeostasis: thermoregulationbehavior is a common method of regulating body temperatureectotherms different microenvironments provide different temperaturesendothermsbehavioral temperature regulation reduces metabolic costs

behavioral temperature regulation in endothermsFigure 41.9

Homeostasis: thermoregulationheat exchange between body and environment occurs through the skinradiation - gain or lossconduction - gain or lossconvection - gain or lossevaporation - loss

Figure 41.10

Homeostasis: thermoregulationheat exchange can be regulated by control of blood flow to the skinconstriction/dilation of blood vessels supplying the skinchange in heart rate

vegetarian marine iguanaFigure 41.11

an iguana regulates body temperature by altering heart rate in surf & sunFigure 41.11

muscular contraction generates heat

brood warming by honey bees

Homeostasis: thermoregulationsome ectotherms use muscular contractions to generate heatinsects flex wing muscles to achieve flight temperatureto warm brood above air temperatureIndian python flexes muscles to warm brood above air temperatureanalogous to mammalian shivering

Homeostasis: thermoregulationanatomical features allow some fish to retain muscular heatin cold fishblood is chilled in gillscold blood is warmed by muscle masswarmed blood returns to gills and is chilled

a cold fish dumps muscular heatFigure 41.12

Homeostasis: thermoregulationanatomical features allow some fish to retain muscular heatin hot fishchilled blood from gills travels near skinchilled blood enters muscle mass next to veins leaving muscle masscountercurrent heat exchange warms blood entering muscle masscountercurrent heat exchange removes heat from blood returning to the gills

a hot fish retains muscular heatFigure 41.12

Homeostasis: thermoregulationthermal characteristics of endothermsthermoneutral zonetemperature window with no regulationbasal metabolic rate meets minimal metabolic needslower critical temperaturebelow which metabolic rate increasesupper critical temperatureabove which active cooling occurs

basal metabolic rate vs. body massFigure 41.13

endotherms regulate body temperature metabolicallyFigure 41.14

Homeostasis: thermoregulationthermal characteristics of endothermsheat generation below the lower critical temperatureshivering heat productioncontractions of opposed musclesreleases heat from ATP hydrolysis

Homeostasis: thermoregulationthermal characteristics of endothermsheat generation below the lower critical temperaturenonshivering heat productionoccurs in brown fat tissuedue to thermogeninuncouples respiratory electron transport from ATP synthesis

brown fat is highly vascularized, has a high density of mitochondria, and has smaller lipid dropletsFigure 41.15

reduced surface area andincreased insulation conserve body heatFigure 41.16

Homeostasis: thermoregulationthermal characteristics of endothermsanatomical features conserve heat below the lower critical temperaturereduced surface/volume ratioincreased thermal insulationoil secretion resists wetting

increased surface area andreduced insulation release body heatFigure 41.16

Homeostasis: thermoregulationthermal characteristics of endothermsheat loss above the upper critical temperatureincreased surface area/volume ratioincreased blood flow to skinevaporationsweat glandspanting

a thermostat controls the effectors (furnace and air conditioner) in a house

metabolic rate and body temperature respond to hypothalamic temperature changesFigure 41.17

ambient temperature(feedforward information)can alter the setpoint for metabolic heat productionFigure 41.18

Homeostasis: thermoregulationmammalian thermal regulationthe mammalian thermostat is the hypothalamusdifferent effectors of thermal regulation have different set pointsenvironmental temperature can act as feed forward information to alter set pointspyrogens increase the set point for metabolic heat production causing fever

Homeostasis: thermoregulationtorpor conserves metabolic resourcestorpor is regulated hypothermiasome birds engage in daily torpor during inactive periodsin hibernating mammals, torpor may last hours, days, or weeks

decreased metabolism, lower temperatureFigure 41.19