Chapter 40 Animal Form
and Function
By: Pham Tran & Princess Montemayor
Overview: Diverse Forms,
Common Challenges
Common set of problems: obtain oxygen, nourish
themselves, excrete waste products and move
Anatomy is the study of the structure of an
Physiology is the study of the functions an
organism performs
Natural selection can fit structure to function
40.1 Physical laws and the
environment constrain animal size
and shape
• Size and shape, “body plans” or “designs,” affect
the way an animal interacts with its environment
• Physical laws limit the evolution of an organism’s
• Convergence evolution occurs because natural
selection shapes similar adaptation when diverse
organisms face the same environmental challenge
Exchange with the Environment
• Size and shape also affect how an animal exchanges
energy and materials with its surroundings
• Body plan must allow all living cells to be bathed in
an aqueous medium, a requirement for maintaining
the fluid integrity of the plasma membranes
• Exchange with the environment occurs as substances
dissolved in the aqueous medium diffuse and are
transported across the cells’ plasma membranes
Amoeba (unicellular protist), entire
surface area is in contact
with the environment.
Hydra consists of two layers of cells with
an aqueous environment circulating in
and out of the hydra’s mouth, being
directly in contact to every one of its cells
– exchanging materials with it.
40.2 Animal form and function
are correlated to all levels of
Tissues are groups of cells with a common
structure and function
Classified under four main categories:
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
Epithelial Tissue
• Epithelial tissue covers the outside of
the body and lines organs and cavities
within the body
• Some are tightly packed to function as a
barrier against mechanical injury,
microbes and fluid loss.
• Glandular epithelia absorb or secrete
chemical solutions.
• Form a mucous membrane: secrete
mucus that lubricates the surface and
keeps it moist.
(Epithelial tissue cont.)
Simple epithelium has a single layer of cells
Stratified epithelium has multiple tiers of cells.
“Pseudostratified” epithelium is single-layered but
appears stratified because the cells vary in
Shape of the cells at exposed surface may be
cuboidal, columnar, or squamous
Connective Tissue
• Connective tissue functions mainly
to bind and support other tissues.
• Sparse population of cells scattered
through an extracellular matrix
• Tissue fibers made of protein:
– Collagenous fibers
– Elastic fibers
– Reticular fibers
Connective tissue (cont.)
Collagenous fibers are made of collagen, most
abundant protein in animal kingdom
Non-elastic, does not tear easily
Ex. Skin on the back of hand
Elastic fibers are long threads made of a protein
called elastin.
Rubbery quality that complements the nonelastic
strength of collagenous fibers
Connective tissue (cont.)
• Reticular fibers are very thin and branched.
• Composed of collagen and continuous with
collagenous fibers to form a tightly woven fabric
that joins connective tissue to adjacent tissues
– Fibroblasts secrete the protein ingredients of
the extracellular fibers.
– Macrophages are amoeboid cells that roam the
maze of fibers, engulfing foreign particles and
the debris of dead cells by phagocytosis.
Muscle Tissue
• Muscle tissue is composed of long
cells called muscle fibers that are
capable of contracting, usually
when stimulated by nerve signals.
• Myofibrils made of the proteins
actin and myosin and serve as
contracting units.
• Vertebrate body has three types of
muscle tissue: skeletal muscle,
cardiac muscle, and smooth muscle
Nervous Tissue
• Nervous tissue senses stimuli and
transmits signals in the form of nerve
impulses from one part of the animal
to another.
• Functional unit is the neuron or
nerve cell, specialized to transmit
nerve impulses.
• Most animals, nervous tissue is
concentrated in the brain, the control
center that coordinates the animal’s
Organ and Organ Systems
• Tissues are combined into functions called
• Many of the organs of vertebrates are suspended
by sheets of connective tissue called mesenteries
in moist or fluid-filled body cavities.
• Mammals have a thoracic cavity housing the
lungs and heart that is separated from the lower
abdominal cavity by a sheet of muscle called the
Organ and Organ Systems
Organ systems are groups of organs that work
together to carry out the major body functions of
most animals.
Efforts of all systems must be coordinated for an
animal to survive.
40.3 Animals use the chemical
energy in food to sustain form
and function
• Bioenergetics limits an animal’s behavior, growth,
and reproduction and determines how much food
it needs.
• Food provides energy-containing molecules after
digested, serves to generate ATP
• Metabolic rate – the amount of energy an animal
uses over time; the sum of all the energyrequiring biochemical reactions occurring over a
given time interval
Bioenergetics of an animal : an
Bioenergetic Strategies
Two basic strategies found in animals:
Endothermic: bodies are warmed by heat
generated by metabolism
Ectothermic: gain heat through external
Metabolic rate is inversely related to size
40.4: Many animals regulate
their internal environment
within relatively narrow limits
Internal environment of vertebrates is called the interstitial fluid.
Fluid fills spaces between vertebrate cells, exchanges nutrients
and wastes with blood contained in microscopic vessels called
Animals tend to maintain relatively constant conditions in their
internal environment, even when the external changes
There are times during development of an animal when major
changes in internal environment are programmed to occur.
Ex: The balance of hormones in human blood is altered
radically during puberty and pregnancy
Homeostasis: steady state or internal balance
A dynamic state, an interplay between outside factors that tend
to change the internal environment and internal control
mechanisms that oppose such changes
Regulating and Conforming
Regulating and conforming are two extremes in how
animals cope with environmental fluctuations
An animal is a regulator for a particular environmental
variable if it uses internal control mechanisms to
moderate internal change in the face of external
An animal is a conformer for a particular environment
variable if it allows its internal condition to vary with
certain external changes.
Regulating and conforming represent extremes on a
continuum and no organism is a perfect regulator or
An animal may maintain homeostasis while regulating some
internal conditions and allowing others to conform to the
Nonliving example of negative
feedback : control of room
Mechanisms of Homeostasis
Mechanism of homeostasis moderate changes in the internal environment.
Any homeostatic control system has three functional components:
(1) Receptor: detects change in some variable of the animals internal environment, such as a change in
body temperature
(2) Control Center: processes information it receives from the receptor and directs an appropriate
response by the (3) effector.
Example: Regulation of Room Temperature
In this case, the control center, a thermostat, contained the receptor, which is a thermometer. When the
room temperature falls below a set point, the thermostat switches on the heater, the effector. When the
thermometer detects a temperature above the set point, the thermostat switches the heater off. This type of
control is called negative feedback, because a change in the variable being monitored triggers the control
mechanism to counteract further change in the same direction
Owing to a time lag between reception and response, the variable drifts slightly above and below the
set point, but the fluctuations are moderate
Negative-feedback mechanisms prevent small changes from becoming too large; most homeostatic
mechanisms in animals operate on this principle of negative feedback.
Positive feedback involves a change in some variable that triggers mechanism that amplify rather than reverse
the change.
Regulated change is essential to normal body functions
Over the short term, homeostatic mechanisms keep body temperature close to a set point, whatever it is at that
particular time, but long term, it allows regulated change in the body’s internal environment
Animals use a considerable amount of energy from eaten food to maintain favorable internal conditions
40.5: Thermoregulation
contributes to homeostasis and
involves anatomy, physiology,
and behavior
Thermoregulation: the process by which animals maintain an
internal temperature within a tolerable range
Critical to survival because most biochemical and physiological
processes are sensitive to changes in body temperature.
Although different animals adapt to different environment
temperatures, each has an optimal temperature range
Thermoregulation helps keep the body temperature within that
optimal range, enabling cells to function most effectively, even as
the external temperature fluctuates
Ectotherms and Endotherms
One way to classify thermal characteristics of animals is to emphasize the role of metabolic heat in determining
body temperature
Ectotherms (invertebrates, fishes, amphibians, lizards, snakes, turtles) gain most of their heat from the
environment. They have such a low metabolic rate that the amount of heat generated is too small to affect
their body temperature
Tolerate greater variation in internal temperature than endotherms
Endotherms ( Mammals, birds, some reptiles and fish, and insects) can use metabolic heat to regulate their
body temperature; in cold temperatures, they generate enough heat to keep their bodies warmer than their
Many maintain high and stable internal temperatures even as the temperature of their surroundings
Animals not classified as ectotherms or endotherms based on whether they have variable or constant body
temperatures, a common misconception.
It’s the source of heat used to maintain body temperature that distinguishes ectotherms from
Another misconception is that ectotherms are “cold-blooded” and endotherms are “warm-blooded”
Ectotherms don’t necessarily have low body temperatures
Ectothermy and endothermy aren’t mutually exclusive thermoregulatory strategies.
Endothermy has several important advantages
Being able to generate a large amount of heat metabolically, along with other biochemical and
physiological adaptations associated with endothermy enables endotherms to perform vigorous
activity for much longer than is possible for most ectotherms.
Enables terrestrial animals to maintain stable body temperatures in the face of environmental
temperature fluctuations that are generally more severe than in aquatic habitats.
Better buffered against external temperature fluctuations compared to ectotherms, but ectotherms
can tolerate larger fluctuations in their internal temperatures.
Endotherms need to consume more food than ectotherms because being endothermic is energetically
Modes of Heat Exchange
Regardless if it’s an ectotherm or endotherm, an organism exchanges eat
by four physical processes:
Conduction: 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
Convection: transfer of heat by the movement of air or liquid past a
surface, as when a breeze contributes to heat loss from a lizards dry
skin, or blood moves heat from the body core to the extremities
Radiation: emission of electromagnetic waves by all objects warmer
than absolute zero. Radiation can transfer heat between objects that
aren’t in direct contact, as when a lizard absorbs heat radiating from
the sun
Evaporation: removal of heat from the surface of a liquid that is losing
some of its molecules as fast. Evaporation of water from a lizard’s
moist surfaces that are exposed to the environment has a strong
cooling effect.
Balancing Heat Loss and Gain
For endotherms, and ectotherms that thermoregulate, the essence of
thermoregulation is managing the heat budget so that rates of heat
gain are equal to rates of heat loss
If heat budget is unbalanced, the animal becomes either warmer or
Five general categories of adaptations help animals thermoregulate
Circulatory Adaptations
Cooling by Evaporative Heat Loss
Behavioral Responses
Adjusting Metabolic Heat Production
A major thermoregulatory adaptation in mammals and birds that reduces
the flow of heat between an animal and its environment and lowers energy
cost of keeping warm
In mammals, insulating material is associated with integumentary system,
the outer covering of the body, consisting of the skin, hair, and nails
Skin functions as a thermoregulatory organ by housing nerves, sweat
glands, blood vessels, and hair follicles and protects internal body parts
from mechanical injury, infection, and drying out.
Consists of two layers, the epidermis and the dermis, underlain by a
tissue layer called the hypodermis
Epidermis is the outermost layer of skin and is composed mostly
of dead epithelial cells that continually flake and fall off. New
cells pushing up from lower layers replace the cells that are lost.
Dermis supports epidermis and contains hair follicles, oil and
sweat glands, muscles, nerves, and blood vessels.
Hypodermis contains adipose tissue, which includes fat-storing
cells and blood vessels. Adipose tissue provides varying degrees
of insulation, depending on the species.
Insulating power of fur or feathers mainly depends on how much still air
the layer traps
Mammalian integumentary
Circulatory Adaptations
Many endotherms and ectotherms can alter amount of blood (and hence
heat) flowing between the body core and the skin
Elevated blood flow in the skin results from vasodilation, an increase in
the diameter of superficial blood vessels triggered by nerve signals that
relax the muscle of the vessel walls.
in endotherms, vasolidation usually warms the skin, increasing the
transfer of body heat to a cool environment by radiation, conduction,
and convection.
Vasoconstriction: reduces blood flow and heat transfer by decreasing the
diameter of superficial vessels
Countercurrent heat exchanger: important for reducing heat loss in may
endotherms, including marine animals and birds.
In some species, blood can go either through the heat exchanger or
bypass it by way of blood vessels. In this way, relative amount of
blood that flows through the two paths may vary, adjusting the rate of
heat loss as an animal’s physiological state or environment changes.
Countercurrent heat exchanger
Cooling by Evaporative Heat
Many Mammals and birds live in places where thermoregulation
requires cooling as well as warming
If environmental temperature is above body temperature,
animals gain heat from the environment and metabolism, and
evaporation is the only way to keep body temperature from
rising rapidly.
Terrestrial animals lose water by evaporation across the skin and
when they breathe. Water absorbs considerable heat when it
evaporates; this heat is carried away from the body surface with
the water vapor
Some animals have adaptations that can greatly augment this
cooling effect like panting
Many terrestrial mammals have sweat glands controlled by
the nervous system
Other mechanisms that promote evaporative cooling include
spreading saliva on body surfaces, or secreting mucus
Behavioral Responses
Both endotherms and ectotherms use behavioral responses to
control body temperature.
Many ectotherms maintain a nearly constant body temperature
through simple behaviors. More complex behavioral adaptations
in some animals include hibernation or migration
All amphibians and most reptiles other than birds are
endothermic which means these organisms control body
temperature mainly by behavior
Optimal temperature range for amphibians varies
substantially with the species
By moving to a location where solar heat is available, an
amphibian can maintain a satisfactory body temperature and
when it’s hot, they move to a cooler area
Adjusting Metabolic Heat
Because endotherms generally maintain body temperatures
considerably warmer than the environment, they must counteract
constant heat loss
Endotherms can vary heat production to match changing rates
of heat loss; heat production is increased by such muscle
activity as moving or shivering
In some mammals, certain hormones can cause mitochondria to
increase their metabolic activity and produce heat instead of ATP.
This nonshivering thermogenesis (NST) takes place throughout the
body, but some mammals also have a tissue called brown fat in the
neck and between the shoulders that is specialized for rapid heat
Through shivering and NST, mammals and birds in cold
environments can increase their metabolic heat production by
as much as five to ten times the minimal levels that occur in
warm conditions.
Feedback Mechanisms in
Regulation of body temperature in humans and other mammals is a complex system
facilitated by feedback mechanisms
Nerve cells that control thermoregulation, as well as those that control many other aspects
of homeostasis, are concentrated in a region of the brain called the hypothalamus
Hypothalamus contains group of nerve cells that functions as a thermostat,
responding to changes in body temperature above or below a set point by activating
mechanisms that promote heat loss or gain
Nerve cells that sense temperature are in the skin, hypothalamus, and several other
body regions
Warm receptors signal the hypothalamic thermostat when temperatures when
temperatures increase; cold receptors signal temperature decrease. At body
temperatures below the normal range, the thermostat inhibits heat loss mechanisms
and activates heat-saving ones such as vasoconstriction of superficial vessels and
erection of fur, while stimulating heat-generating mechanisms
In response to elevated body temperature, the thermostat shuts down heat retention
mechanisms and promotes body cooling by vasolidation, sweating, or panting. The
thermostat can also respond to external temperature even without changes in body
core temperature
Adjustment to Changing
Many animals can adjust to a new range of environmental temperatures over a period of days or
weeks, a physiological response called acclimatization
Both ectotherms and endotherms acclimatize, but in different ways. In birds and mammals,
acclimatization includes adjusting amount of insulation by growing or shedding fur
Helps endotherms keep constant body temperature in warm and cold seasons
Acclimatization responses in ectotherms often include adjustments at the cellular level. Cells
may increase certain enzymes or produce variants of enzymes that have the same function but
different optimal temperatures.
Membranes may also change proportions of saturated and unsaturated lipids they contain,
which helps keep membranes fluid at different temperatures
Some ectotherms protect themselves by producing “antifreeze” compounds that prevent ice
formation in the cells
Cells can often make rapid adjustments to temperature changes. Mammalian cells respond
to a marked increase in temperature and to other forms of severe stress by accumulating
molecules called stress-induced proteins, including heat shock proteins
Within minutes of being shocked, the cells begin synthesizing heat-shock proteins to
help maintain the integrity of other proteins that would be denatured by severe heat
Stress induced proteins help prevent cell death when an organism is challenged by
severe changes in the cellular environment
Torpor and Energy
Despite their many adaptations for homeostasis, animals may occasionally encounter
conditions that severely challenge their abilities to balance heat, energy, and materials
An adaptation that enables animals to save energy while avoiding difficult and dangerous
conditions is torpor, a physiological state in which activity is low and metabolism decreases
Hibernation: long-term torpor that is an adaptation to winter cold and food scarcity.
When vertebrate endotherms enter torpor or hibernation, their body temperatures
decline-in effect, their body’s thermostat is turned down
Resulting energy savings due to lower metabolic rate and less heat production are
huge; metabolic rates during hibernation can be several hundred times lower than if
the animal attempted to maintain normal body temperatures
This allows hibernators to survive very long periods on limited supplies of
energy stored in the body tissues or as food cached in a burrow
Estivation, or summer torpor, also characterized by slow metabolism and inactivity
enables animals to survive long periods of high temperatures and scarce water supplies.
Many small mammals and birds exhibit a daily torpor that seems to be adapted to their
feeding patterns
An animals daily cycle of activity and torpor appears to be a built-in rhythm controlled
by its biological clock
Campbell, Neil A., and Jane B. Reece. Biology. AP ed. Vol. 7th. San Francisco: Pearson
Education, 2005. Print.
E., Marino F. Thermoregulation and Human Performance. NSW: Bathurst, 2008. Print.
"Homeostasis." - Definition from Web. 07 Mar. 2012.
Pack, Philips. Biology 2nd Edition. New York: Wiley, 2001. Print.
"Tissue (biology)." Wikipedia. Wikimedia Foundation, 03 July 2012. Web. 07 Mar. 2012.
"Thermoregulation." Wikipedia. Wikimedia Foundation, 03 June 2012. Web. 07 Mar. 2012.
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