Chapter 40:

Basic Principles of Animal Form & Function

Rob Swatski

Associate Professor of Biology

HACC – York Campus

1

Exchange with the Environment

• An animal’s size & shape directly affect how it exchanges energy & materials with its environment

• Exchange occurs as dissolved substances diffuse & are transported across the cells’ plasma membranes

• A unicellular protist living in

water has enough surface area of plasma membrane to service its entire volume of cytoplasm

2

Multicellular organisms with a

sac body plan have body walls that are only 2 cells thick, which facilitates

diffusion

3

More complex organisms have highly folded internal surfaces for exchanging materials

0.5 cm Nutrients

Digestive system

Lining of small intestine

Mouth Food

External environment

Animal body

CO2 O2

Circulatory system

Heart

Respiratory system

Cells

Interstitial fluid

Excretory system

Anus

Unabsorbed matter (feces)

Metabolic waste products (nitrogenous waste)

Kidney tubules

10 µm

50

µm

Lung tissue

4

Epithelial Tissue

Cuboidal

epithelium Simple columnar epithelium

Pseudostratified

ciliated

columnar epithelium

Stratified squamous epithelium

Simple squamous

epithelium

5

Connective Tissue Collagenous fiber

Loose connective tissue

Elastic fiber 12

0 µ

m Cartilage

Chondrocytes

10

0 µ

m

Chondroitin sulfate

Adipose tissue

Fat droplets

15

0 µ

m

White blood cells

55

µm

Plasma Red blood cells

Blood

Nuclei

Fibrous connective tissue

30

µm

Osteon

Bone

Central canal

70

0 µ

m

6

Muscle Tissue

50 µm Skeletal muscle

Multiple nuclei

Muscle fiber

Sarcomere

100 µm

Smooth muscle

Cardiac muscle

Nucleus

Muscle fibers

25 µm

Nucleus Intercalated disk

7

Glial cells

Nervous Tissue

15 µm

Dendrites

Cell body

Axon

Neuron

Axons

Blood vessel

40 µm

8

Coordination and Control

• Depends on both the endocrine & nervous systems

• The endocrine system: transmits chemical signals (hormones) to receptive cells throughout the body via blood

- a hormone may affect 1 or more regions throughout the body

• Hormones are relatively slow acting, but can have long-lasting effects

9

Stimulus

Endocrine cell

Hormone

Signal travels everywhere via the bloodstream.

Blood vessel

Response

(a) Signaling by hormones 10

• The nervous system: transmits information between specific locations

• The information conveyed depends on a nerve signal’s (impulse) pathway, not the type of signal

- impulse transmission is very fast

- impulses can be received by neurons, muscle cells, & endocrine cells

11

Stimulus

Neuron

Axon Signal

Signal travels along axon to a specific location.

Signal

Axons

Response

(b) Signaling by neurons 12

Feedback Control Loops

• Animals manage their internal environment by regulating or conforming to the external environment

• Regulators: use internal control mechanisms to moderate internal change in the face of external, environmental fluctuation

• Conformers: allow internal conditions to vary with certain external changes

13

River otter (temperature regulator)

Largemouth bass (temperature conformer)

Bo

dy

tem

pe

ratu

re (

°C)

0 10

10

20

20

30

30

40

40

Ambient (environmental) temperature (ºC) 14

Homeostasis

• Organisms use homeostasis to maintain a “steady state” (internal balance) regardless of external environment

• In humans, body temperature, blood pH, & glucose concentration are each maintained at a constant level

15

Mechanisms of Homeostasis

• Moderate changes in the internal environment

• For a given variable, fluctuations above or below a set point act as a stimulus

- stimuli are detected by a sensor & trigger a response

- the response returns the variable back to the set point

16

Response: Heater turned off

Stimulus: Control center (thermostat) reads too hot

Room temperature

decreases

Set point: 20ºC

Room temperature

increases

Stimulus: Control center (thermostat)

reads too cold

Response: Heater turned on 17

Homeostasis

Stimulus: Perturbation/stress

Response/effector

Control center

Sensor/receptor 18

Feedback Loops in Homeostasis

• The dynamic equilibrium of most homeostasis is maintained by negative feedback loops

- helps to return a variable to either a normal range or a set point

- buildup of the end product shuts the system off

• Positive feedback loops: do not usually contribute much to homeostasis

19

Alterations in Homeostasis

• Set points & normal ranges can change with age or show cyclic variation

• Homeostasis can adjust to changes in external environment, a process called acclimatization

20

Thermoregulation: process where animals maintain an internal temperature within a tolerable range

• Ectothermic animals: gain heat from external sources

- include most invertebrates, fishes, amphibians, & reptiles

• Endothermic animals: generate heat by metabolism

- birds & mammals

21

• Ectotherms generally tolerate more internal temperature variations

• Endotherms are active at a greater range of external temperatures

- more energetically expensive than ectothermy

22

Variation in Body Temperature

• Poikilotherm: body temperature varies with its environment

• Homeotherm: body temperature is relatively constant

23

Balancing Heat Loss and Gain

Organisms exchange heat by 4 physical processes:

Conduction

Convection

Radiation

Evaporation

24

Radiation Evaporation

Convection Conduction 25

Heat regulation in mammals often involves the integumentary system: skin, hair, & nails

Epidermis

Dermis

Hypodermis

Adipose tissue

Blood vessels

Hair

Sweat pore

Muscle

Nerve

Sweat gland

Oil gland

Hair follicle 26

5 general adaptations help animals thermoregulate:

– Insulation

– Circulatory adaptations

– Cooling by evaporative heat loss

– Behavioral responses

– Adjusting metabolic heat production 27

Insulation

Major thermoregulatory adaptation in mammals & birds

Skin, feathers, fur, & blubber reduce heat flow between an animal & its environment

28

Circulatory Adaptations

• Regulation of blood flow near the body surface significantly affects thermoregulation

• Many endotherms (& some ectotherms) can alter the amount of blood flowing between the body core & the skin

- Vasodilation: blood flow in the skin increases, facilitating heat loss

- Vasoconstriction: blood flow in the skin decreases, reducing heat loss

29

• The arrangement of blood vessels in many marine mammals & birds allows for countercurrent exchange

- transfer heat between fluids flowing in opposite directions

- important mechanism for minimizing heat loss

30

Canada goose Bottlenose dolphin

Artery

Artery

Vein Vein

Blood flow

33º 35ºC

27º 30º

18º 20º

10º 9º

31

Some bony fishes & sharks also use countercurrent heat exchange

Many endothermic insects also use this to help maintain a high temperature in the thorax

32

Cooling by Evaporative Heat Loss

• Many types of animals lose heat through evaporation of water in sweat

• Panting increases the cooling effect in birds & many mammals

• Sweating or bathing moistens the skin, helping to cool an animal down

33

Behavioral Responses

• Both endotherms & ectotherms use behavioral responses to control body temperature

- some terrestrial invertebrates have postures that minimize or maximize absorption of solar heat

34

Adjusting Metabolic Heat Production

• Some animals can regulate body temperature by adjusting their rate of metabolic heat production

• Heat production is increased by muscle activity (moving or shivering)

35

RESULTS

Contractions per minute

O2 c

on

sum

pti

on

(m

L O

2/h

r) p

er

kg

0 0

20

20 15 10 5 25 30 35

40

60

80

100

120

36

PREFLIGHT PREFLIGHT WARM-UP

FLIGHT

Thorax

Abdomen

Time from onset of warm-up (min)

Tem

pe

ratu

re (

ºC)

0 2 4

25

30

35

40

37

Acclimatization in Thermoregulation

• Birds & mammals can vary their insulation to acclimatize to seasonal temperature changes

• When temperatures are subzero, some

ectotherms produce “antifreeze” compounds to prevent ice formation in their cells

- “plugs” gaps in existing crystals

38

39

Physiological Thermostats and Fever

• Thermoregulation is controlled by a region of the brain called the hypothalamus

- triggers heat loss or heat-generating mechanisms

• Fever is the result of a change to the set point for a biological thermostat

40

Sweat glands secrete sweat, which evaporates, cooling the body.

Thermostat in hypothalamus activates cooling mechanisms.

Blood vessels in skin dilate: capillaries fill; heat radiates from skin.

Increased body temperature

Decreased body temperature

Thermostat in hypothalamus activates warming mechanisms.

Blood vessels in skin constrict, reducing heat loss.

Skeletal muscles contract; shivering generates heat.

Body temperature increases; thermostat

shuts off warming mechanisms.

Homeostasis:

Internal temperature of 36–38°C

Body temperature decreases; thermostat

shuts off cooling mechanisms.

41

Energy requirements are related to animal size, activity, and environment

• Bioenergetics: the overall flow & transformation of energy in an animal

• It determines how much food an animal needs & relates to an animal’s size, activity, & environment

42

Energy Allocation and Use

• Animals harvest chemical energy from food

• Energy-containing molecules from food are usually used to make ATP, which powers cellular work

• After the needs of staying alive are met, remaining food molecules can be used in biosynthesis

• Biosynthesis includes body growth & repair, synthesis of storage material (fat), & production of gametes

43

Organic molecules in food External

environment

Animal body Digestion and

absorption

Nutrient molecules in body cells

Carbon skeletons

Cellular respiration

ATP

Heat

Energy lost in feces

Energy lost in nitrogenous waste

Heat

Biosynthesis

Heat

Heat

Cellular work

44

Quantifying Energy Use

• Metabolic rate: the amount of energy an animal uses in a unit of time

• Measured by determining the amount of O2 consumed or CO2 produced

45

Minimum Metabolic Rate and Thermoregulation

• Basal metabolic rate (BMR): the metabolic rate of an endotherm at rest at a “comfortable” temperature

• Standard metabolic rate (SMR): the metabolic rate of an ectotherm at rest at a specific temperature

• Both rates assume a nongrowing, fasting, & nonstressed animal

• Ectotherms have much lower metabolic rates than endotherms of a comparable size

46

Shrew

Harvest mouse

Mouse

Ground squirrel

Rat

Cat Dog

Sheep

Human

Horse

Elephant

Body mass (kg) (log scale)

BM

R (

L O

2/h

r) (

log

scal

e)

(a) Relationship of BMR to body size

10–3 10–2 10–2

10–1

10–1

1

1

10 102 103

10

102

103

47

Size and Metabolic Rate

• Metabolic rate per gram is inversely related to body size among similar animals

- 1 g of mouse body mass requires 20-times more calories than 1 g of elephant body mass!

• Smaller animals have a higher metabolic rate per gram

- leads to a higher O2 delivery rate, breathing rate, heart rate, & greater (relative) blood volume, compared with a larger animal

- must also eat much more food per unit of body mass

48

103 102 10 1 10–1 10–2 10–3 0

1

2

3

4

5

6

7

8

Body mass (kg) (log scale)

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

BM

R (

L O

2/h

r) (

pe

r kg

) Shrew

Harvest mouse

Mouse

Rat

Ground squirrel

Cat

Sheep

Dog Human

Horse

Elephant

49

Activity and Metabolic Rate

• Activity greatly affects metabolic rate for endotherms & ectotherms

• In general, the maximum metabolic rate an animal can sustain is inversely related to the duration of the activity

50

Energy Budgets

• Different species use energy & materials in food in different ways, depending on their environment

• Use of energy is partitioned to BMR (or SMR), activity, thermoregulation, growth, & reproduction

51

An

nu

al e

ne

rgy

exp

en

dit

ure

(kc

al/h

r)

60-kg female human from temperate climate

800,000

Basal (standard) metabolism

Reproduction Thermoregulation

Growth

Activity

340,000

4-kg male Adélie penguin from Antarctica (brooding)

4,000

0.025-kg female deer mouse from temperate North America

8,000

4-kg female eastern indigo snake

Endotherms Ectotherm

52

Torpor and Energy Conservation

• Torpor: physiological state in which activity is low & metabolism decreases

- enables animals to save energy while avoiding difficult & dangerous conditions

• Hibernation: long-term torpor that is an adaptation to winter cold & food scarcity

53

Additional metabolism that would be necessary to stay active in winter Actual

metabolism

Arousals

Body temperature

Outside temperature

Burrow temperature

Met

abo

lic r

ate

(k

cal p

er

day

) Te

mp

era

ture

(°C

)

June August October December February April –15

–10

–5

0

5

15

10

25

20

35

30

0

100

200

54

Estivation (summer torpor): enables animals to

survive long periods of high temperatures and scarce water supplies

Daily torpor: exhibited by many small birds &

mammals

- adapted to feeding patterns

55