Chapter 40Basic Principlesof Animal Formand Function

Overview: Diverse Forms, CommonChallenges

Anatomy is the study of the biological form of anorganismPhysiology is the study of the biological functions anorganism performsThe comparative study of animals reveals that formand function are closely correlated

Concept 40.1Animal form and function arecorrelated at all levels oforganization

Size and shape affect the way an animalinteracts with its environmentMany different animal body plans have evolvedand are determined by the genome

Physical Constraints on Animal Sizeand Shape

The ability to performcertain actions depends

size, and environmentEvolutionaryconvergence reflects

adaptations to a similarenvironmentalchallengePhysical laws imposeconstraints on animalsize and shape

(a) Tuna

(b) Penguin

(c) Seal

Exchange with the Environment

exchanges energy and materials with itssurroundingsExchange occurs as substances dissolved in theaqueous medium diffuse and are transported

A single-celled protist living in water has a sufficientsurface area of plasma membrane to service itsentire volume of cytoplasmMulticellular organisms with a sac body plan havebody walls that are only two cells thick, facilitatingdiffusion of materials

Exchange

0.15 mm

(a) Single cell

1.5 mm

(b) Two layers of cells

Exchange

Exchange

Mouth

Gastrovascularcavity

More complex organisms have highly foldedinternal surfaces for exchanging materials

0.5 cmNutrients

Digestivesystem

Lining of small intestine

MouthFood

External environment

Animalbody

CO2 O2

Circulatorysystem

Heart

Respiratorysystem

Cells

Interstitialfluid

Excretorysystem

Anus

Unabsorbedmatter (feces)

Metabolic waste products(nitrogenous waste)

Kidney tubules

10 µm

Lung tissue

Exchange with the EnvironmentIn vertebrates, the space between cells is filled withinterstitial fluid, which allows for the movement ofmaterial into and out of cellsA complex body plan helps an animal in a variableenvironment to maintain a relatively stable internalenvironment

Hierarchical Organization of BodyPlans

Most animals are composed of specialized cellsorganized into tissues that have different functionsTissues make up organs, which together make uporgan systemsTissue Structure and FunctionDifferent tissues have different structures that aresuited to their functionsTissues are classified into four main categories:epithelial, connective, muscle, and nervous

Epithelial TissueEpithelial tissue covers the outside of the body andlines the organs and cavities within the bodyIt contains cells that are closely joinedThe shape of epithelial cells may be cuboidal (likedice), columnar (like bricks on end), or squamous(like floor tiles)The arrangement of epithelial cells may be simple(single cell layer), stratified (multiple tiers of cells), orpseudostratified (a single layer of cells of varyinglength)

Epithelial TissueCuboidalepithelium

Simplecolumnarepithelium

Pseudostratifiedciliatedcolumnarepithelium

Stratifiedsquamousepithelium

Simplesquamousepithelium

Apical surface

Basal surfaceBasal lamina

40 µm

Connective TissueConnective tissue mainly binds and supports other tissuesIt contains sparsely packed cells scattered throughoutan extracellular matrixThe matrix consists of fibers in a liquid, jellylike, or solidfoundationThere are three types of connective tissue fiber, all madeof protein:

Collagenous fibers provide strength and flexibilityElastic fibers stretch and snap back to their original lengthReticular fibers join connective tissue to adjacent tissues

Connective tissue contains cells, includingFibroblasts that secrete the protein of extracellular fibersMacrophages that are involved in the immune system

Connective TissueIn vertebrates, the fibers and foundation combineto form six major types of connective tissue:

Loose connective tissue binds epithelia to underlyingtissues and holds organs in placeCartilage is a strong and flexible support materialFibrous connective tissue is found in tendons, whichattach muscles to bones, and ligaments, whichconnect bones at jointsAdipose tissue stores fat for insulation and fuelBlood is composed of blood cells and cell fragments inblood plasmaBone is mineralized and forms the skeleton

Connective Tissue

Collagenous fiberLooseconnectivetissue

Elastic fiber

Cartilage

Chondrocytes

Chondroitinsulfate

Adiposetissue

Fat droplets

White blood cells

Plasma Red bloodcells

Blood

Nuclei

Fibrousconnectivetissue

OsteonBone

Central canal

Muscle TissueMuscle tissue consists of long cells called muscle fibers,which contract in response to nerve signalsIt is divided in the vertebrate body into three types:

Skeletal muscle, or striated muscle, is responsible forvoluntary movementSmooth muscle is responsible for involuntary body activitiesCardiac muscle is responsible for contraction of the heart

Muscle Tissue

50 µmSkeletalmuscle

MultiplenucleiMuscle fiberSarcomere

100 µm

Smoothmuscle

Cardiac muscle

Nucleus

Musclefibers

25 µm

Nucleus Intercalateddisk

Nervous TissueNervous tissue senses stimuli and transmits signalsthroughout the animalNervous tissue contains:

Neurons, or nerve cells, that transmit nerve impulsesGlial cells, or glia, that help nourish, insulate, andreplenish neurons

Glial cells

Nervous Tissue

15 µm

DendritesCell body

Axon

Neuron

Axons

Blood vessel

40 µm

Coordination and ControlControl and coordination within a bodydepend on the endocrine system andthe nervous systemThe endocrine system transmitschemical signals called hormones toreceptive cells throughout the body viabloodA hormone may affect one or moreregions throughout the bodyHormones are relatively slow acting, butcan have long-lasting effects

Stimulus

Hormone

Endocrinecell

Signal travelseverywherevia thebloodstream.

Bloodvessel

Response

(a) Signaling by hormones

Coordination and ControlThe nervous system transmits informationbetween specific locationsThe information conveyed depends on

signalNerve signal transmission is very fastNerve impulses can be received byneurons, muscle cells, and endocrinecells

Stimulus

Neuron

AxonSignal

Signal travelsalong axon toa specificlocation.

Signal

Axons

Response

(b) Signaling by neurons

Concept 40.2Feedback control loops maintainthe internal environment in manyanimals

Animals manage their internal environment byregulating or conforming to the externalenvironment

Regulating and ConformingA regulator usesinternal controlmechanisms tomoderate internalchange in the face ofexternal,environmentalfluctuationA conformer allows itsinternal condition tovary with certainexternal changes

River otter (temperature regulator)

Largemouth bass(temperature conformer)

0 10

10

20

20

30

30

40

40

Ambient (environmental) temperature (ºC)

HomeostasisOrganisms use homeostasis

environmentIn humans, body temperature, blood pH, andglucose concentration are each maintained at aconstant level

Mechanisms ofHomeostasis

Mechanisms ofhomeostasis moderatechanges in the internalenvironmentFor a given variable,fluctuations above orbelow a set point serve asa stimulus; these aredetected by a sensor andtrigger a responseThe response returns thevariable to the set point

Response:Heaterturnedoff

Stimulus:Control center(thermostat)reads too hot

Roomtemperaturedecreases

Setpoint:20ºC

Roomtemperature

increases

Stimulus:Control center(thermostat)

reads too cold

Response:Heaterturnedon

Feedback Loops in HomeostasisThe dynamic equilibrium of homeostasis ismaintained by negative feedback, which helps toreturn a variable to either a normal range or a setpointMost homeostatic control systems function bynegative feedback, where buildup of the endproduct shuts the system offPositive feedback loops occur in animals, but donot usually contribute to homeostasis

Alterations in HomeostasisSet points and normal ranges can change with ageor show cyclic variationHomeostasis can adjust to changes in externalenvironment, a process called acclimatization

Concept 40.3Homeostatic processes forthermoregulation involve form,function, and behaviour

Thermoregulation is the process by which animalsmaintain an internal temperature within atolerable range

Endothermy and EctothermyEndothermic animals generate heat by metabolism;birds and mammals are endothermsEctothermic animals gain heat from externalsources; ectotherms include most invertebrates,fishes, amphibians, and non-avian reptilesIn general, ectotherms tolerate greater variation ininternal temperature, while endotherms are activeat a greater range of external temperaturesEndothermy is more energetically expensive thanectothermy

Variation in Body TemperatureThe body temperature of a poikilotherm varies withits environment, while that of a homeotherm isrelatively constantOrganisms exchangeheat by four physicalprocesses: conduction,convection, radiation,and evaporation

Radiation Evaporation

Convection Conduction

Body Heat Loss and GainHeat regulation in mammals often involves theintegumentary system: skin, hair, and nailsFive general adaptations help animalsthermoregulate:

InsulationCirculatory adaptationsCooling by evaporative heat lossBehavioral responsesAdjusting metabolic heat production

ThermoregulationInsulation

Insulation is a major thermoregulatory adaptation inmammals and birdsSkin, feathers, fur, and blubber reduce heat flowbetween an animal and its environment

Circulatory AdaptationsRegulation of blood flow near the body surfacesignificantly affects thermoregulationMany endotherms and some ectotherms can alter theamount of blood flowing between the body core andthe skinIn vasodilation, blood flow in the skin increases,facilitating heat lossIn vasoconstriction, blood flow in the skin decreases,lowering heat loss

ThermoregulationCirculatory Adaptationscontinued

The arrangement of bloodvessels in many marinemammals and birds allowsfor countercurrentexchangeCountercurrent heatexchangers transfer heatbetween fluids flowing inopposite directionsCountercurrent heatexchangers are animportant mechanism forreducing heat loss

Canadagoose

Bottlenosedolphin

ArteryArtery

Vein VeinBlood flow

33º35ºC27º30º

18º20º

10º 9º

ThermoregulationCooling by Evaporative Heat Loss

Many types of animals lose heat through evaporation ofwater in sweatPanting increases the cooling effect in birds and manymammalsSweating or bathing moistens the skin, helping to cool ananimal down

Behavioural ResponseBoth endotherms and ectotherms usebehavioral responses to control bodytemperatureSome terrestrial invertebrates have posturesthat minimize or maximize absorption of solarheat

ThermoregulationAdjusting Metabolic Heat Production

Some animals can regulate body temperature byadjusting their rate of metabolic heat productionHeat production is increased by muscle activitysuch as moving or shiveringSome ectotherms can also shiver to increase bodytemperature

Contractions per minute0

0

20

2015105 25 30 35

40

60

80

100

120 PREFLIGHT PREFLIGHTWARM-UP

FLIGHTThorax

Abdomen

Time from onset of warm-up (min)0 2 4

25

30

35

40

Acclimatization in Thermoregulation

Birds and mammals can vary their insulation toacclimatize to seasonal temperature changesWhen temperatures are subzero, some ectotherms

formation in their cells

PhysiologicalThermostats andFever

Thermoregulation iscontrolled by a region ofthe brain called thehypothalamusThe hypothalamus triggersheat loss or heatgenerating mechanismsFever is the result of achange to the set point fora biological thermostat

Sweat glands secretesweat, which evaporates,cooling the body.

Thermostat inhypothalamusactivates coolingmechanisms.

Blood vesselsin skin dilate:capillaries fill;heat radiatesfrom skin. Increased body

temperature

Decreased bodytemperature

Thermostat inhypothalamusactivates warmingmechanisms.

Blood vessels in skinconstrict, reducingheat loss.

Skeletal muscles contract;shivering generates heat.

Body temperatureincreases; thermostat

shuts off warmingmechanisms.

Homeostasis:Internal temperature

of 36 38°C

Body temperaturedecreases;thermostat

shuts off coolingmechanisms.

Concept 40.4Energy requirements are related toanimal size, activity, andenvironment

Bioenergetics is the overall flow andtransformation of energy in an animalIt determines how much food an animal needs

environment

Energy Allocation and UseAnimals harvest chemicalenergy from foodEnergy-containingmolecules from food areusually used to make ATP,which powers cellularworkAfter the needs of stayingalive are met, remainingfood molecules can beused in biosynthesisBiosynthesis includes bodygrowth and repair,synthesis of storagematerial such as fat, andproduction of gametes

Organic moleculesin foodExternal

environmentAnimalbody Digestion and

absorption

Nutrient moleculesin body cells

Carbonskeletons

Cellularrespiration

ATP

HeatEnergy lostin feces

Energy lost innitrogenouswaste

Heat

Biosynthesis

Heat

Heat

Cellularwork

Metabolic Rate andThermoregulation

Metabolic rate is the amount of energy an animaluses in a unit of timeOne way to measure it is to determine the amountof oxygen consumed or carbon dioxide producedBasal metabolic rate (BMR) is the metabolic rate of

temperatureStandard metabolic rate (SMR) is the metabolic rateof an ectotherm at rest at a specific temperatureBoth rates assume a nongrowing, fasting, andnonstressed animalEctotherms have much lower metabolic rates thanendotherms of a comparable size

Influences on Metabolic RateMetabolic rates are affected by many factorsbesides whether an animal is an endotherm orectothermTwo of these factors are size and activity

Size andMetabolic Rate

Metabolic rate per gram isinversely related to bodysize among similar animalsResearchers continue tosearch for the causes ofthis relationshipThe higher metabolic rateof smaller animals leads toa higher oxygen deliveryrate, breathing rate, heartrate, and greater (relative)blood volume, comparedwith a larger animal

Elephant

Horse

HumanSheep

DogCat

RatGround squirrel

MouseHarvest mouse

Shrew

Body mass (kg) (log scale)10 3 10 2

10 2

10 1

10 1

10

10

1

1 102

102

103

103

(a) Relationship of BMR to body size

Shrew

Mouse

Harvest mouse

SheepRat Cat

DogHuman

HorseElephant

Ground squirrel

Body mass (kg) (log scale)10 3 10 2 10 1 1 10 102 103

0

1

2

3

4

5

6

8

7

(b) Relationship of BMR per kilogram of body mass to body size

Activity and Metabolic RateActivity greatly affects metabolic rate forendotherms and ectothermsIn general, the maximum metabolic rate an animalcan sustain is inversely related to the duration of theactivity

Energy BudgetsDifferent species use energy and materials in food indifferent ways, depending on their environmentUse of energy is partitioned to BMR (or SMR),activity, thermoregulation, growth, andreproduction

60-kg female humanfrom temperate climate

800,000Basal(standard)metabolism

ReproductionThermoregulation

Growth

Activity

340,000

4-kg male Adélie penguinfrom Antarctica (brooding)

4,000

0.025-kg female deer mousefrom temperateNorth America

8,000

4-kg female easternindigo snake

Endotherms Ectotherm

Torpor and Energy ConservationTorpor is a physiological state in which activity is lowand metabolism decreasesTorpor enables animals to save energy whileavoiding difficult and dangerous conditionsHibernation is long-term torpor that is an adaptationto winter cold and food scarcityEstivation, or summer torpor, enables animals tosurvive long periods of high temperatures andscarce water suppliesDaily torpor is exhibited by many small mammalsand birds and seems adapted to feeding patterns