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CHAPTER 40 - 42
ANIMAL STRUCTURE AND
FUNCTION
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Introduction
The study of animal form and function is
integrated by the common set of problems
that all animals must solve.
These include how to extract oxygen from the
environment, how to nourish themselves, how
to excrete waste products, and how to move.
Animals of diverse evolutionary histories
and varying complexities must solve these
general challenges of life.
Animal form and function reflects
biology’s major themes
Animals provide vivid examples evolution in
their forms and functions.
The adaptations observed in a comparative
study of animals evolved by natural
selection.
For example, the long, tonguelike proboscis of
a hawkmoth is a structural adaptation for
feeding.
Recoiled when not in use,
the proboscis extends as a
straw through which the
moth can suck nectar from
deep within tube-shaped flowers.
Fig. 40.0
Animals show a correlation between
structure and function.
Form fits function at all the levels of life,
from molecules to organisms.
Knowledge of a structure provides insight
into what it does and how its works.
Conversely, knowing the function of a
structure provides insight about its
construction.
Anatomy is the study of the structure
of an organism.
Physiology is the study of the functions
an organism performs.
The form-function principle is just another
extension of biology’s central theme of
evolution.
Function correlates with structure in the tissues
of organisms
Life is characterized by hierarchical levels
of organization, each with emergent
properties.
Animals are multicellular organisms with
their specialized cells grouped into
tissues.
In most animals, combinations of various
tissues make up functional units called
organs, and groups of organs that work
together form organ systems.
For example, the human digestive system
consists of a stomach, small intestine, large
intestine, and several other organs, each a
composite of different tissues.
Tissues are groups of cell with a common
structure and function.
A tissue may be held together by a sticky
extracellular matrix that coats the cells or
weaves them together in a fabric of fibers.
Tissues are classified into four main
categories: epithelial tissue, connective
tissue, nervous tissue, and muscle tissue.
Epithelia are classified by the number
of cell layers and the shape of the cells
on the free surface.
 A simple epithelium has
a single layer of cells, and
a stratified epithelium
has multiple tiers of cells.
 The shapes of cells may
be cuboidal (like dice),
columnar (like bricks on
end), or squamous (flat
like floor tiles).
Fig. 40.1
Connective tissue functions mainly to
bind and support other tissues.
Connective tissues have a sparse population
of cells scattered through a heavy
extracellular matrix.
The matrix generally consists of a web of
fibers embedding in a uniform foundation
that may be liquid, jellylike, or solid.
The major types of connective tissues in
vertebrates are loose connective tissue,
adipose tissue, fibrous connective tissue,
cartilage, bone, and blood.
Fig. 40.2
Adipose tissue is a specialized form of
loose connective tissues that store fat in
adipose cells distributed throughout the
matrix.
Adipose tissue pads and insulates the body
and stores fuel as fat molecules.
Each adipose cell contains a large fat
droplet that swells when fat is stored and
shrinks when the body uses fat as fuel.
You do not loose or gain adipose cells they
just change in size.
Nervous tissue senses stimuli and transmits
signals from one part of the animal to
another.
 The functional unit of nervous tissue is the neuron,
or nerve cell.
 It consists of a cell body and two or more
extensions, called dendrites and axons.
Fig. 40.3
Muscle tissue is composed of long cells
called muscle fibers that are capable of
contracting when stimulated by nerve
impulses.
Arranged in parallel within the cytoplasm of
muscle fibers are large numbers of
myofibrils made of the contractile proteins
actin and myosin.
Muscle is the most abundant tissue in most
animals, and muscle contraction accounts for
most of the energy-consuming cellular work
in active animals.
 There are three types of muscle tissue in the
vertebrate body: skeletal muscle, cardiac
muscle, and smooth muscle.
Fig. 40.4
The organ systems of animals are
interdependent
In all but the simplest animals (sponges
and some cnidarians) different tissues are
organized into organs.
Organ systems carry out the major body
functions of most animals.
Each organ system consists of several organs
and has specific functions.
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Organism’s body structure
An animal’s size and shape, often called
body plans or designs, are fundamental
aspects of form and function that
significantly affect the way an animal
interacts with its environment.
 Similarly, the laws of hydrodynamics constrain
the shapes that are possible for aquatic
organisms that swim very fast.
 Tunas, sharks, penguins, dolphins, seal, and
whales are all fast swimmers and all have the
same basic shape, called a fusiform shape.
 This shape
minimizes drag
in water, which is
about a thousand
times denser
than air.
Fig. 40.6
The similar forms of speedy fishes,
birds, and marine mammals are a
consequence of convergent evolution in
the face of the universal laws of
hydrodynamics.
Convergence occurs because natural
selection shapes similar adaptations when
diverse organisms face the same
environmental challenge, such as the
resistance of water to fast travel.
Convergent evolution
Most animals are complex and made up of
compact masses of cells, producing outer
surfaces that are relatively small
compared to their volume.
Most organisms have
extensively folded or
branched internal surfaces
specialized for exchange
with the environment.
The circulatory system
shuttles material among
all the exchange surfaces
within the animal.
Fig. 40.8
Regulating the internal environment
Animals tend to maintain relatively
constant conditions in their internal
environment, even when the external
environment changes.
While a pond-dwelling hydra is powerless to
affect the temperature of the fluid that
bathes its cells, the human body can
maintain its “internal pond” at a more-or-less
constant temperature of about 370C.
Homeostasis depends on feedback
circuits
Any homeostatic control system has three
functional components: a receptor, a
control center, and an effector.
The receptor detects a change in some
variable in the animal’s internal environment,
such as a change in temperature.
The control center processes the information
it receives from the receptor and directs an
appropriate response by the effector.
One type of control circuit, a negativefeedback system, can control the
temperature in a room.
In this case, the control center, called a
thermostat, also contains the receptor, a
thermometer.
When room temperature
falls, the thermostat
switches on the heater,
the effector.
Fig. 40.9a
In a negative-feedback system, 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 receptor 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.
Our own body
temperature is
kept close to a set
point of 37oC by
the cooperation of
several negativefeedback circuits
that regulate
energy exchange
with the
environment.
Fig. 40.9b
In contrast to negative feedback, positive
feedback involves a change in some variable
that trigger mechanisms that amplify rather
than reverse the change.
For example, during childbirth, the pressure of
the baby’s head against sensors near the opening
of the uterus stimulates uterine contractions.
These cause greater pressure against the
uterine opening, heightening the contractions,
which cause still greater pressure.