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.
Annual energy expenditure (kcal/yr)
Endotherms
Activity 340,000
costs
8,000
4,000
Energy expenditure per unit mass
(kcal/kg•day)
60-kg female human
from temperate climate
(a) Total annual energy expenditures
Figure 40.10a, b
Ectotherm
800,000 BasalReproduction Temperature
regulation costs
metabolic
rate
Growth
4-kg male Adélie penguin
from Antarctica (brooding)
0.025-kg female deer mouse 4-kg female python
from temperate
from Australia
North America
438
Human
233
Deer mouse
(b) Energy expenditures per unit mass (kcal/kg•day)
Python
Adélie penguin
36.5
5.5
• 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
• 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.
Temperature Conformers and
Regulators
• In general, ectotherms are temperature conformers and
endotherms regulators
40
Endotherms use
homeostatic mechanisms to
maintain a constant internal
thermal environment
Body temperature (°C)
River otter (endotherm)
30
20
Largemouth bass (ectotherm)
10
0
Figure 40.12
10
20
30
40
Ambient (environmental) temperature (°C)
Thermostats control heating in houses
• A homeostatic control system has three
functional components Heating system in a house
– A receptor, a control center, and an effector
Response
No heat
produced
Heater
turned
off
Room
temperature
decreases
Too
hot
Set
point
Too
cold
Set
point
Set point
Control center:
thermostat
Room
temperature
increases
Heater
turned
on
Response
Figure 40.11
Heat
produced
• 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 and Endotherms
• 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.
• 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.
Figure 40.13
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.
Evaporation is the removal of heat from the surface of a
liquid 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.
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.
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
• In mammals, the integumentary system
– Acts as insulating material
Hair
Epidermis
Sweat
pore
Muscle
Dermis
Nerve
Sweat
gland
Hypodermis
Adipose tissue
Figure 40.14
Blood vessels
Oil gland
Hair follicle
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 (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.
Countercurrent heat exchangers
• Many marine mammals and birds
– Have arrangements of blood vessels called
countercurrent heat exchangers that are
important for reducing heat loss
1 Arteries carrying warm blood down the
legs of a goose or the flippers of a dolphin
are in close contact with veins conveying
cool blood in the opposite direction, back
toward the trunk of the body. This
arrangement facilitates heat transfer
from arteries to veins (black
arrows) along the entire length
of the blood vessels.
Canada
goose
Artery
1
35°C
30º
20º
18º
10º
9º
2
Figure 40.15
2 Near the end of the leg or flipper, where
arterial blood has been cooled to far below
Vein
the animal’s core temperature, the artery
can still transfer heat to the even colder
3
blood of an adjacent vein. The venous blood
33°
continues to absorb heat as it passes warmer
and warmer arterial blood traveling in the
opposite direction.
27º
Pacific
bottlenose
dolphin
1
3
Blood flow
3
Vein
Artery
2
3 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 parts
immersed in cold water.
In the flippers of a dolphin, each artery is
surrounded by several veins in a
countercurrent arrangement, allowing
efficient heat exchange between arterial
and venous blood.
Hot Tunas and Sharks
• Some specialized bony fishes and sharks
– Also possess countercurrent heat exchangers
21º
25º 23º
27º
(a) Bluefin tuna. Unlike most fishes, the bluefin tuna maintains
temperatures in its main swimming muscles that are much higher
than the surrounding water (colors indicate swimming muscles cut
in transverse section). These temperatures were recorded for a tuna
in 19°C water.
(b) Great white shark. Like the bluefin tuna, the great white shark
has a countercurrent heat exchanger in its swimming muscles that
reduces the loss of metabolic heat. All bony fishes and sharks lose
heat to the surrounding water when their blood passes through the
gills. 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 gills
is conveyed via large arteries just under the skin, keeping cool blood
away from the body core. As shown in the enlargement, small
arteries carrying cool blood inward from the large arteries under the
skin are paralleled by small veins carrying warm blood outward from
the inner body. This countercurrent flow retains heat in the muscles.
Figure 40.16a, b
29º
31º
Body cavity
Skin
Artery
Vein
Blood
vessels
in gills
Heart
Capillary
network within
muscle
Artery and
vein under Dorsal aorta
the skin
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.
Conductive & Evaporative Heat Loss
• Bathing moistens the skin
– Which helps to cool an animal down
Figure 40.18
Behavioral Responses
• Both endotherms and ectotherms
– Use a variety of behavioral responses to
control body temperature
• 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
Moth flight in sub-zero temperatures
• Many species of flying insects
– Use shivering to warm up before taking flight
PREFLIGHT
Temperature (°C)
40
PREFLIGHT
WARMUP
FLIGHT
Thorax
35
30
Abdomen
25
0
2
Time from onset of warmup (min)
Figure 40.20
4
Feedback Mechanisms in
Thermoregulation
• Thermoregulation most well developed in
mammals and birds.
• Mammals regulate their body temperature
– By a complex negative feedback system that
involves several organ systems
Temperature regulation in mammals
• In humans, a specific part
of the brain, the
hypothalamus
– Contains a group of nerve
cells that function as
a thermostat
Sweat glands secrete
sweat that evaporates,
cooling the body.
Thermostat in
hypothalamus
activates cooling
mechanisms.
Increased body
temperature (such
as when exercising
or in hot
surroundings)
Blood vessels
in skin dilate:
capillaries fill
with warm blood;
heat radiates from
skin surface.
Homeostasis:
Internal body temperature
of approximately 36–38C
Body temperature
increases;
thermostat
shuts off warming
mechanisms.
Some sense cold and others heat.
Body temperature
decreases;
thermostat
shuts off cooling
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.
Figure 40.21
Skeletal muscles rapidly
contract, causing shivering,
which generates heat.
Thermostat in
hypothalamus
activates
warming
mechanisms.
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 in Rodents
• 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.
Additional metabolism that would be
necessary to stay active in winter
Metabolic rate
(kcal per day)
200
Actual
metabolism
100
0
35
30
Temperature (°C)
Why do they periodically wake
up? Not know for sure, but
maybe they need to sleep!???
Re-establish ion gradients? Bears!
Figure 40.22
Arousals
Body
temperature
25
20
15
10
5
0
-5
Outside
temperature
Burrow
temperature
-10
-15
June
August
October
December
February
April
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.