Form and Function (2)Chpt 40 all

4-3-06

• An animal’s use of energy– Is partitioned to BMR (or SMR), activity, homeostasis, growth, and

reproduction– Small animals have higher metabolic rates than large animals on a

unit weight basis when similar forms compared. No explanation for this yet!

– Ectotherms—much lower rates than endotherms. Snake’s meals are large but few and far between meals. Reabsorption of intestinal lining.

Endotherms Ectotherm

Ann

ual e

nerg

y ex

pend

iture

(kc

al/y

r)

800,000 Basalmetabolicrate

ReproductionTemperatureregulation costs

Growth

Activitycosts

60-kg female humanfrom temperate climate

Total annual energy expenditures (a)

340,000

4-kg male Adélie penguinfrom Antarctica (brooding)

4,000

0.025-kg female deer mousefrom temperateNorth America

8,000

4-kg female pythonfrom Australia

Ene

rgy

expe

nditu

re p

er u

nit

mas

s (k

cal/k

g•da

y)

438

Deer mouse

233

Adélie penguin

36.5

Human

5.5

Python

Energy expenditures per unit mass (kcal/kg•day)(b)Figure 40.10a, b

• Concept 40.4: Animals regulate their internal environment within relatively narrow limits

• The internal environment of vertebrates– Is called the interstitial fluid (IF), but includes the blood

and cytoplasm and is very different from the external environment. Cytoplasm ion composition is also different than the blood. IF is the blood less red blood cells and blood proteins.

• Homeostasis is a balance between external changes– And the animal’s internal control mechanisms that

oppose the changes

• Regulating and conforming– Are two extremes in how animals cope with

environmental fluctuations– Regulators use internal control mechanisms to

moderate internal change in the face of external, environmental fluctuation.

– Conformers allow internal condition to vary with certain external changes. Examples would be body temperature in Endotherms and Ectotherms as well as ion composition of blood and seawater.

Regulating and Conforming

• In general, ectotherms are temperature conformers and endotherms regulators

Temperature Conformers and Regulators

Figure 40.12

River otter (endotherm)

Largemouth bass (ectotherm)

Ambient (environmental) temperature (°C)

Bod

y te

mpe

ratu

re (

°C)

40

30

20

10

10 20 30 400

Endotherms usehomeostatic mechanisms to maintain a constant internal thermal environment

Thermostats control heating in houses• A homeostatic control system has three

functional components– A receptor, a control center, and an effector

Figure 40.11

Response

No heatproduced

Roomtemperaturedecreases

Heaterturnedoff

Set point

Toohot

Setpoint

Control center:thermostat

Roomtemperatureincreases

Heaterturnedon

Toocold

Response

Heatproduced

Setpoint

Heating system in a house

• Most homeostatic control systems function by negative feedback– Where buildup of the end product of the system shuts the system

off

• A second type of homeostatic control system is positive feedback– Which involves a change in some variable that triggers

mechanisms that amplify the change– Example of hormone in stomach where presence of acid

stimulates secretion of more acid until low pH overrides the positive feedback and shuts down the acid secretion.

• Concept 40.5: Thermoregulation contributes to homeostasis and involves anatomy, physiology, and behavior

• Thermoregulation– Is the process by which animals maintain an internal

temperature within a tolerable range– Optimum temperature for animals. Animals adapted to

their particular environment. Polar animals can’t live in the tropics. Tropic animals can’t adjust to polar temperatures.

• Ectotherms– Include most invertebrates, fishes, amphibians, and non-bird

reptiles

• Endotherms - Include birds and mammals

Heterotherms --endotherm part of the time and ectotherm at night.

Ectotherms and Endotherms

• Endothermy is more energetically expensive than ectothermy– But buffers animals’ internal temperatures against

external fluctuations– And enables the animals to maintain a high level of

aerobic metabolism that are responsive to energy needs without the complications of temperature change. Decrease in temperature decreases rate of biochemical reactions (digestion slower, muscle contraction slower etc). These processes have a temperature quotient of 10. For each 10 degree increase in T the reaction rate increase 2 to 3 fold (Q10).

– Example of Marine iguanas that eat sea algae.

Modes of Heat Exchange• Organisms exchange heat by four physical

processes. Example of marine iguana.Radiation is the emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that are not in direct contact, as when a lizard absorbs heat radiating from the sun.

Evaporation is the removal of heat from the surface of aliquid that is losing some of its molecules as gas. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect.

Convection is the transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizard’s dry skin, or blood moves heat from the body core to the extremities.

Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when a lizard sits on a hot rock.

Figure 40.13

Balancing Heat Loss and Gain

• Thermoregulation involves physiological and behavioral adjustments– That balance heat gain and loss

Insulation

• Insulation, which is a major thermoregulatory adaptation in mammals and birds– Reduces the flow of heat between an animal

and its environment– May include feathers, fur, or blubber

Hair

Sweatpore

Muscle

Nerve

Sweatgland

Oil glandHair follicle

Blood vessels

Adipose tissue

Hypodermis

Dermis

Epidermis

• In mammals, the integumentary system– Acts as insulating material

Figure 40.14

• Many endotherms and some ectotherms– Can alter the amount of blood flowing between the body core and

the skin

• In vasodilation– Blood flow in the skin increases, facilitating heat loss (arterioles)

• In vasoconstriction– Blood flow in the skin decreases, lowering heat loss– Some human more susceptible to frost bite than others. Blood

flow shuts off to extremeties.

Circulatory Adaptations

• Many marine mammals and birds– Have arrangements of blood vessels called

countercurrent heat exchangers that are important for reducing heat loss

Countercurrent heat exchangers

In the flippers of a dolphin, each artery issurrounded by several veins in acountercurrent arrangement, allowingefficient heat exchange between arterialand venous blood.

Canadagoose

Artery Vein

35°C

Blood flow

VeinArtery

30º

20º

10º

33°

27º

18º

9º

Pacific bottlenose dolphin

2

1

3

2

3

Arteries carrying warm blood down thelegs of a goose or the flippers of a dolphinare in close contact with veins conveyingcool blood in the opposite direction, backtoward the trunk of the body. Thisarrangement facilitates heat transferfrom arteries to veins (blackarrows) along the entire lengthof the blood vessels.

1

Near the end of the leg or flipper, wherearterial blood has been cooled to far below the animal’s core temperature, the artery can still transfer heat to the even colderblood of an adjacent vein. The venous bloodcontinues to absorb heat as it passes warmer and warmer arterial blood traveling in the opposite direction.

2

As the venous blood approaches the center of the body, it is almost as warm as the body core, minimizing the heat lost as a result of supplying blood to body partsimmersed in cold water.

3

Figure 40.15

1 3

Hot Tunas and Sharks• Some specialized bony fishes and sharks

– Also possess countercurrent heat exchangers

Figure 40.16a, b

21º25º 23º

27º

29º31º

Body cavity

SkinArtery

Vein

Capillarynetwork withinmuscle

Dorsal aortaArtery andvein underthe skin

Heart

Bloodvesselsin gills

(a) Bluefin tuna. Unlike most fishes, the bluefin tuna maintainstemperatures in its main swimming muscles that are much higherthan the surrounding water (colors indicate swimming muscles cutin transverse section). These temperatures were recorded for a tunain 19°C water.

(b) Great white shark. Like the bluefin tuna, the great white sharkhas a countercurrent heat exchanger in its swimming muscles thatreduces the loss of metabolic heat. All bony fishes and sharks loseheat to the surrounding water when their blood passes through thegills. However, endothermic sharks have a small dorsal aorta, and as a result, relatively little cold blood from the gills goes directly to the core of the body. Instead, most of the blood leaving the gillsis conveyed via large arteries just under the skin, keeping cool bloodaway from the body core. As shown in the enlargement, smallarteries carrying cool blood inward from the large arteries under theskin are paralleled by small veins carrying warm blood outward fromthe inner body. This countercurrent flow retains heat in the muscles.

Hot Moths• Many endothermic insects

– Have countercurrent heat exchangers that help maintain a high temperature in the thorax. Infrared photo with bright red the warmest temperature

Figure 40.17

Cooling by Evaporative Heat Loss

• Many types of animals– Lose heat through the evaporation of water

in sweat (pigs go to the mud cuz lack sweat glands).

– Use panting to cool their bodies. Water on tongue evaporates. Evaporation of a gram of water takes up 570 calories of heat.

• Bathing moistens the skin– Which helps to cool an animal down

Conductive & Evaporative Heat Loss

Figure 40.18

• Both endotherms and ectotherms– Use a variety of behavioral responses to

control body temperature

Behavioral Responses

• Some terrestrial invertebrates– Have certain postures that enable them to minimize

or maximize their absorption of heat from the sun

Figure 40.19

Adjusting Metabolic Heat Production

• Some animals can regulate body temperature in the cold– By adjusting their rate of metabolic heat

production

• Many species of flying insects– Use shivering to warm up before taking flight

Moth flight in sub-zero temperatures

Figure 40.20

PREFLIGHT PREFLIGHTWARMUP

FLIGHT

Thorax

Abdomen

Tem

per

atur

e (°

C)

Time from onset of warmup (min)

40

35

30

25

0 2 4

• Thermoregulation most well developed in mammals and birds.

• Mammals regulate their body temperature– By a complex negative feedback system that

involves several organ systems

Feedback Mechanisms in Thermoregulation

• In humans, a specific part of the brain, the hypothalamus– Contains a group of nerve

cells that function as a thermostat

Temperature regulation in mammalsThermostat inhypothalamusactivates coolingmechanisms.

Sweat glands secrete sweat that evaporates, cooling the body.

Blood vesselsin skin dilate:capillaries fillwith warm blood;heat radiates fromskin surface. Body temperature

decreases;thermostat

shuts off coolingmechanisms.

Increased bodytemperature (suchas when exercising

or in hotsurroundings)

Homeostasis:Internal body temperatureof approximately 36–38C

Body temperatureincreases;thermostat

shuts off warmingmechanisms.

Decreased bodytemperature

(such as whenin cold

surroundings)

Blood vessels in skinconstrict, diverting bloodfrom skin to deeper tissuesand reducing heat lossfrom skin surface.

Skeletal muscles rapidlycontract, causing shivering,which generates heat.

Thermostat inhypothalamusactivateswarmingmechanisms.Figure 40.21

Some sense cold and others heat.

Adjustment to Changing Temperatures

• In a process known as acclimatization– Many animals can adjust to a new range of

environmental temperatures over a period of days or weeks

– Acclimation takes place in laboratory with only one variable being altered (ie temperature)

• Acclimatization may involve cellular adjustments such as membrane lipid changes and elaboration of temperature specific enzymes– Or in the case of birds and mammals,

adjustments of insulation and metabolic heat production

Torpor and Energy Conservation

• Torpor– Is an adaptation that enables animals to

save energy while avoiding difficult and dangerous conditions

– Is a physiological state in which activity is low and metabolism decreases

• Hibernation is long-term torpor– That is an adaptation to winter cold and food

scarcity during which the animal’s body temperature declines. Alaskan ground squirrels allow their body to become supercooled.

Hibernation in Rodents

Additional metabolism that would benecessary to stay active in winter

Actualmetabolism

Bodytemperature

Arousals

Outsidetemperature Burrow

temperature

June August October December February April

Tem

pera

ture

(°C

)M

etab

olic

rat

e(k

cal p

er d

ay)

200

100

0

35

30

25

20

15

10

5

0

-5

-10

-15

Figure 40.22

Why do they periodically wakeup? Not know for sure, but maybe they need to sleep!???Re-establish ion gradients? Bears!

Estivation

• Estivation, or summer torpor (some ground squirrels and other rodents)– Enables animals to survive long periods of high

temperatures and scarce water supplies• Daily torpor

– Is exhibited by many small mammals and birds and seems to be adapted to their feeding patterns (Humming birds). To costly to maintain high body temperature at night.