1. Exchange with the Environment
An animal’s size and shape directly affect how it exchanges energy and materials with its surroundings
Exchange occurs as substances dissolved in the aqueous medium diffuse and are transported across the cells’ plasma membranes
A single-celled protist living in water has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm

2. Mouth
Gastrovascular
cavity
Diffusion
Diffusion
Diffusion
Single cell
Two cell layers

3. Multicellular organisms with a sac body plan have body walls that are only two cells thick, facilitating diffusion of materials
More complex organisms have highly folded internal surfaces for exchanging materials

4. External environment CO2 Food O2 Mouth Animal body Respiratory system
Blood
50 µm
0.5 cm
A microscopic view of the lung reveals that it is much more spongelike than balloonlike. This construction provides an expansive wet surface for gas exchange with the environment (SEM).
Cells
Heart
Nutrients
Circulatory
system
10 µm
Digestive
system
Interstitial
fluid
Excretory
system
The lining of the small intestine, a digestive organ, is elaborated with fingerlike projections that expand the surface area for nutrient absorption (cross-section, SEM).
Anus
Inside a kidney is a mass of microscopic tubules that exchange chemicals with blood flowing through a web of tiny vessels called capillaries (SEM).
Unabsorbed
matter (feces)
Metabolic waste
products (urine)

5. Tissue Structure and Function
Tissues make up organs, which together make up organ systems
Different tissues have different structures that are suited to their functions
Tissues are classified into four main categories: epithelial, connective, muscle, and nervous

6. Simple Stratified columnar columnar epithelium epithelium
EPITHELIAL TISSUE
Columnar epithelia, which have cells with relatively large cytoplasmic volumes, are often located where secretion or active absorption of substances is an important function.
Simple
columnar
epithelium
Stratified
columnar
epithelium
Pseudostratified
ciliated columnar
epithelium
Cuboidal
epithelia
Stratified
squamous
epithelia
Simple squamous
epithelia
Basement membrane
40 µm

7. Chondrocytes Collagenous fiber Loose connective tissue Chondroitin
120 µm
Chondrocytes
Collagenous
fiber
Loose
connective
tissue
Chondroitin
sulfate
Elastic
fiber
100 µm
Cartilage
Fibrous
connective tissue
Adipose tissue
Fat droplets
Nuclei
150 µm
30 µm
Blood
Central
canal
Red blood cells
Bone
White blood cell
Osteon
Plasma
700 µm
55 µm

8. Multiple nuclei Skeletal muscle Muscle fiber Sarcomere Cardiac muscle
MUSCLE TISSUE
100 µm
Multiple
nuclei
Skeletal muscle
Muscle fiber
Sarcomere
Cardiac muscle
Nucleus
Intercalated
disk
50 µm
Nucleus
Smooth muscle
Muscle
fibers
25 µm
NERVOUS TISSUE
Neuron
Process
Cell body
Nucleus
50 µm

9. Epithelial tissue covers the outside of the body and lines the organs and cavities within the body
Connective tissue mainly binds and supports other tissues
Muscle tissue consists of long cells called muscle fibers, which contract in response to nerve signals
It is divided in the vertebrate body into three types: skeletal, cardiac, and smooth
Nervous tissue senses stimuli and transmits signals throughout the animal

10. Lumen of
stomach
Mucosa: an epithelial
layer that lines the
lumen
Submucosa: a matrix of
connective tissue that
contains blood vessels
and nerves
Muscularis: consists
mainly of smooth muscle
tissue
Serosa: a thin layer of
connective and epithelial
tissue external to the muscularis
0.2 mm

11. Influences on Metabolic Rate
Metabolic rates are affected by many factors besides whether an animal is an endotherm or ectotherm
Two of these factors are size and activity
Amphibians and reptiles other than birds are ectothermic: They gain their heat mostly from external sources
Ectotherms generally have lower metabolic rates

12. Activity and Metabolic Rate
The basal metabolic rate (BMR) is the metabolic rate of an endotherm at rest
Activity greatly affects metabolic rate
Different species use energy and materials in food in different ways, depending on their environment
Use of energy is partitioned to BMR, activity, homeostasis, growth, and reproduction

13. Maximum metabolic rate
500
A = 60-kg alligator A H
100 H A
A = 60-kg human 50 H
Maximum metabolic rate
(kcal/min; log scale) 10 H 5 H A 1 A
0.5 A
0.1 1
second 1
minute 1
hour 1
day 1
week
Time interval
Key
Existing intracellular ATP
ATP from glycolysis
ATP from aerobic respiration

14. Endotherms Ectotherm 800,000 340,000 8,000 4,000 438 Human 233 Python
Reproduction
Basal
(standard)
metabolism
Temperature
regulation
Growth
Activity
Annual energy expenditure (kcal/yr)
340,000
8,000
4,000
60-kg female human
from temperate climate
4-kg male Adélie penguin
from Antarctica (brooding)
0.025-kg female deer mouse
from temperate
North America
4-kg female python
from Australia
Total annual energy expenditures. The slices of the pie charts indicate energy
expenditures for various functions.
438
Human
Energy expenditure per unit mass
(kcal/kg•day)
233
Python
Deer mouse
Adélie penguin
36.5
5.5
Energy expenditures per unit mass (kcal/kg•day). Comparing the daily energy expenditures per kg of body weight for the four animals reinforces two important concepts of bioenergetics. First, a small animal, such as a mouse, has a much greater energy demand per kg than does a large animal of the same taxonomic class, such as a human (both mammals). Second, note again that an ectotherm, such as a python, requires much less energy per kg than does an endotherm of equivalent size, such as a penguin.

15. Animals regulate their internal environment within relatively narrow limits
The internal environment of vertebrates is called the interstitial fluid and is very different from the external environment
Homeostasis is a balance between external changes and the animal’s internal control mechanisms that oppose the changes

16. Mechanisms of Homeostasis
A homeostatic control system has three functional components: a receptor, a control center, and an effector
Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off
In positive feedback, a change in a variable triggers mechanisms that amplify rather than reverse the change

17. Response
No heat
produced
Heater
turned
off
Room
temperature
decreases
Set
point
Too
hot
Set point
Set
point
Too
cold
Control center:
thermostat
Room
temperature
increases
Heater
turned on
Response
Heat
produced

18. Ectotherms and Endotherms
Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range
Ectotherms include invertebrates, fishes, amphibians, and reptiles
Endotherms include birds and mammals
In general, ectotherms tolerate greater variation in internal temperature than endotherms

19. 40
River otter (endotherm) 30
Body temperature (°C) 20
Largemouth bass (ectotherm) 10 10 20 30 40
Ambient (environmental) temperature (°C)

20. Endothermy is more energetically expensive than ectothermy
It buffers the animal’s internal temperatures against external fluctuations
It also enables the animal to maintain a high level of aerobic metabolism
Organisms exchange heat by four physical processes: conduction, convection, radiation, and evaporation

21. Radiation
Evaporation
Convection
Conduction

22. Balancing Heat Loss and Gain
In thermoregulation, physiological and behavioral adjustments balance heat loss and gain
Five general adaptations help animals thermoregulate:
Insulation
Circulatory adaptations
Cooling by evaporative heat loss
Behavioral responses
Adjusting metabolic heat production

23. Insulation
Insulation is a major thermoregulatory adaptation in mammals and birds
It reduces heat flow between an animal and its environment
Examples are skin, feathers, fur, and blubber
In mammals, the integumentary system acts as insulating material

24. Hair
Epidermis
Sweat
pore
Muscle
Dermis
Nerve
Sweat
gland
Hypodermis
Adipose tissue
Blood vessels
Oil gland
Hair follicle

25. Circulatory Adaptations
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
In vasoconstriction, blood flow in the skin decreases, lowering heat loss

26. Many marine mammals and birds have an arrangement of blood vessels called a countercurrent heat exchanger
Countercurrent heat exchangers are important for reducing heat loss
Some bony fishes and sharks also have countercurrent heat exchangers

27. Canada goose Pacific bottlenose dolphin Blood flow Artery Vein Vein
33°
30°
27°
20°
18°
10° 9°

28. Skin
Artery
Vein
Blood
vessels
in gills
Capillary
network within
muscle
Heart
Artery and
vein under
the skin
Dorsal aorta
Great white shark

29. Cooling by Evaporative Heat Loss
Many types of animals lose heat through evaporation of water in sweat
Panting augments the cooling effect in birds and many mammals
Bathing moistens the skin, helping to cool an animal down

30. Both endotherms and ectotherms use behavioral responses to control body temperature
Some terrestrial invertebrates have postures that minimize or maximize absorption of solar heat

31. Adjusting Metabolic Heat Production
Some animals can regulate body temperature by adjusting their rate of metabolic heat production
Many species of flying insects use shivering to warm up before taking flight

32. Feedback Mechanisms in Thermoregulation
Mammals regulate body temperature by negative feedback involving several organ systems
In humans, the hypothalamus (a part of the brain) contains nerve cells that function as a thermostat

33. Internal body temperature
Thermostat in
hypothalamus
activates cooling
mechanisms.
Sweat glands secrete
sweat that evaporates,
cooling the body.
Blood vessels
in skin dilate:
capillaries fill
with warm blood;
heat radiates from
skin surface.
Increased body
temperature (such
as when exercising
or in hot
surroundings)
Body temperature
decreases;
thermostat
shuts off cooling
mechanisms.
Homeostasis:
Internal body temperature
of approximately 36–38°C
Body temperature
increases;
thermostat
shuts off warming
mechanisms.
Decreased body
temperature
(such as when
in cold
surroundings)
Blood vessels in skin
constrict, diverting blood
from skin to deeper tissues
and reducing heat loss
from skin surface.
Thermostat in
hypothalamus
activates
warming
mechanisms.
Skeletal muscles rapidly
contract, causing shivering,
which generates heat.

34. Adjustment to Changing Temperatures
In acclimatization, many animals adjust to a new range of environmental temperatures over a period of days or weeks
Acclimatization may involve cellular adjustments or (as in birds and mammals) adjustments of insulation and metabolic heat production

35. Torpor and Energy Conservation
Torpor is a physiological state in which activity is low and metabolism decreases
Torpor enables animals to save energy while avoiding difficult and dangerous conditions
Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity

36. Additional metabolism that would be
necessary to stay active in winter
200
Actual
metabolism
Metabolic rate
(kcal per day)
100
Arousals 35
Body
temperature 30 25 20
Temperature (°C) 15 10 5 –5
Outside
temperature
Burrow
temperature
–10
–15
June
August
October
December
February
April

37. Estivation, or summer torpor, 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 adapted to feeding patterns

38. Animations and Videos Bozeman – Thermoregulation
Bozeman - Anatomy and Physiology
Bozeman - Organ Systems
Chapter Quiz Questions – 1
Chapter Quiz Questions – 2