Chapter 40: Physiology, Homeostasis, and Temperature Regulation
CHAPTER 40
Physiology, Homeostasis, and
Temperature Regulation
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Chapter 40: Physiology,
Homeostasis, and
Temperature Regulation
Homeostasis: Maintaining the Internal
Environment
Tissues, Organs, and Organ Systems
Physiological Regulation and Homeostasis
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Chapter 40: Physiology,
Homeostasis, and
Temperature Regulation
Temperature and Life
Maintaining Optimal Body Temperature
Thermoregulation in Endotherms
The Vertebrate Thermostat
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Homeostasis: Maintaining the
Internal Environment
• Single-celled organisms and some small,
simple multicellular animals meet their
needs by direct exchange between their
cells and an aqueous environment.
• Larger, more complex animals must do so
by maintaining a constant internal
environment.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Homeostasis: Maintaining the
Internal Environment
• The internal environment consists of the
extracellular fluids.
• Organs and organ systems have specialized
functions to keep certain aspects of the
internal environment in a constant state.
Review Figure 40.1
5
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure 40.1
Figure 40.1
figure 40-01.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Homeostasis: Maintaining the
Internal Environment
• Homeostasis is the maintenance of
constancy in the internal environment
• It depends on the ability to control and
regulate organ and organ system function.
7
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Tissues, Organs and Organ
Systems
• Cells with a similar structure and function
make up a tissue.
• There are four general types:
Epithelial
 Connective
 Muscle
 Nervous.
Review Figure 40.2

8
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
figure 40-02.jpg
Figure 40.2
Figure 40.2
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Tissues, Organs, and Organ
Systems
• Epithelial tissues are sheets of tightly
connected cells that cover body surfaces
and line hollow organs.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Tissues, Organs, and Organ
Systems
• Connective tissues support and reinforce
other tissues.
• They generally consist of dispersed cells in
an extracellular matrix.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Tissues, Organs, and Organ
Systems
• Muscle tissues contract.
• There are three types:
Skeletal
 Cardiac
 Smooth.

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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Tissues, Organs, and Organ
Systems
• There are two types of nerve cells:
• Neurons generate and transmit
electrochemical signals
• Glial cells provide supporting functions for
neurons.
13
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Tissues, Organs, and Organ
Systems
• Organs consist of multiple tissue types, and
organs make up organ systems. Review
Table 40.1
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Table 40.1
– Part 1
Table 40.1 – Part 1
table 40-01a.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Table 40.1
– Part 2
Table 40.1 – Part 2
table 40-01b.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Physiological Regulation and
Homeostasis
• Regulatory systems have set points and
respond to feedback information.
• Negative feedback corrects deviations from
the set point
• Positive feedback amplifies responses
• Feedforward information changes the set
point. Review Figure 40.5
17
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.5
Figure 40.5
figure 40-05.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Temperature and Life
• Living systems require a range of
temperatures between the freezing point of
water and the temperatures that denature
proteins.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Temperature and Life
• Most biological processes and reactions are
temperature-sensitive.
• Q10 is a measure of temperature sensitivity.
Review Figure 40.6
20
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure 40.6
Figure 40.6
figure 40-06.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Temperature and Life
• Animals that cannot avoid seasonal changes
in body temperature have biochemical
adaptations to compensate.
• These enable animals to acclimatize to
seasonal changes.
Review Figure 40.7
22
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.7
Figure 40.7
figure 40-07.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Maintaining Optimal Body
Temperature
• Homeotherms maintain a fairly constant
body temperature most of the time;
poikilotherms do not.
• Endotherms produce metabolic heat;
ectotherms depend mostly on environmental
sources of heat.
Review Figure 40.8
24
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
figure 40-08.jpg
Figure 40.8
Figure 40.8
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Maintaining Optimal Body
Temperature
• Ectotherms and endotherms can regulate
body temperature through behavior.
Review Figure 40.9
26
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure 40.9
Figure 40.9
figure 40-09.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Maintaining Optimal Body
Temperature
• Heat exchange between a body and the
environment is via:
radiation
 conduction
 convection
 Evaporation
Review Figure 40.11

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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.11
Figure 40.11
figure 40-11.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Maintaining Optimal Body
Temperature
• Ectotherms and endotherms can control
heat exchange with the environment by
altering blood flow to the skin.
Review
Figure 40.12
30
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.12
Figure 40.12
figure 40-12.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Maintaining Optimal Body
Temperature
• Some ectotherms can produce metabolic
heat to raise their body temperatures.
Review Figure 40.13
32
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.13
Figure 40.13
figure 40-13.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Maintaining Optimal Body
Temperature
• Some fish have circulatory systems that
function as countercurrent heat exchangers
to conserve heat produced by muscle
metabolism. Review Figure 40.14
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure 40.14
– Part 1
Figure 40.14 – Part 1
figure 40-14a.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure 40.14
– Part 2
Figure 40.14 – Part 2
figure 40-14b.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Thermoregulation in
Endotherms
• Endotherms have high basal metabolic
rates.
• Over a range of environmental
temperatures, the thermoneutral zone, their
resting metabolic rates remain at basal
levels.
Review Figure 40.15
37
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.15
Figure 40.15
figure 40-15.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Thermoregulation in
Endotherms
• When environmental temperature falls
below a lower critical temperature,
endotherms maintain their body
temperatures through shivering and
nonshivering metabolic heat production.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Thermoregulation in
Endotherms
• When environmental temperature rises
above an upper critical temperature,
metabolic rate increases as a consequence
of evaporative water loss.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Thermoregulation in
Endotherms
• Endotherms in cold climates have
adaptations that minimize heat loss:
a reduced surface area-to-volume
ratio
 increased insulation.

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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Thermoregulation in
Endotherms
• Endotherms may dissipate excess heat
generated by exercise or the environment
via evaporation.
• However, water loss can be dangerous to
endotherms in dry environments.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
The Vertebrate Thermostat
• The vertebrate thermostat is in the
hypothalamus.
• It has set points for activating
thermoregulatory responses.
• Hypothalamic temperature provides
negative feedback information.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
The Vertebrate Thermostat
• Cooling the hypothalamus induces blood
vessel constriction and increased metabolic
heat production
• Heating it induces blood vessel dilation and
active evaporative water loss.
• Thermoregulatory behaviors are induced by
changes in hypothalamic temperature.
Review Figure 40.18
44
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.18
Figure 40.18
figure 40-18.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
The Vertebrate Thermostat
• Changes in set point reflect the integration
of information that is relevant to the
regulation of body temperature.
Review Figure 40.19
46
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure
40.19
Figure 40.19
figure 40-19.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
The Vertebrate Thermostat
• Fever, which results from a rise in set point,
helps the body fight infections.
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Chapter 40: Physiology, Homeostasis, and Temperature Regulation
The Vertebrate Thermostat
• Adaptations in which set points are reduced
to conserve energy include daily torpor and
hibernation.
Review Figure 40.20
49
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure 40.20
– Part 1
Figure 40.20 – Part 1
figure 40-20a.jpg
Chapter 40: Physiology, Homeostasis, and Temperature Regulation
Figure 40.20
– Part 2
Figure 40.20 – Part 2
figure 40-20b.jpg