CHAPTER 43: The Animal Body and Principles of Regulation
WHERE DOES IT ALL FIT IN?
Chapter 43 builds on the foundations of Chapter 32 and provides detailed information about animal
form and function Students should be encouraged to recall the principles of eukaryotic cell structure
and evolution associated with the particular features of animal cells. Multicellularity should also be
reviewed. The information in chapter 43 does not stand alone and fits in with the remaining chapters
on animals. Students should know that animals and other organisms are interrelated and originated
from a common ancestor of all living creatures on Earth.
SYNOPSIS
The human organism is a vertebrate, therefore it is also a deuterostome and a coelomic animal.
The diaphragm divides the body into the thoracic cavity containing the lungs and the heart and
the peritoneal cavity containing the stomach, liver, intestines, and various other organs. It is
supported by an internal skeleton of jointed bones. A skull surrounds the brain and the hollow
vertebral column surrounds the dorsal nerve cord. All vertebrates are organized in successively
more inclusive levels: cells to tissues to organs to organ systems. Humans contain eleven
principal organ systems, each a collection of functional units composed of several different
tissues. The tissues themselves are derived from embryonic endoderm, mesoderm, and ectoderm
and are of four main types: epithelial, connective, muscle, and nervous tissue.
Epithelium protects other tissues from dehydration and damage and provides a selective barrier.
Simple epithelium is only a single cell layer thick; the cells may exhibit squamous (flattened,
irregular), cuboidal, or columnar shapes. Stratified epithelium is a few cell layers thick and is
made up of a combination of cell shapes. The outer epithelium of terrestrial vertebrates is highly
keratinized for protection against abrasion and dehydration. Glands are epithelial tissues that
serve a secretory function. Exocrine glands are connected to epithelium by ducts while endocrine
glands are ductless and secrete their hormonal products directly into the blood system.
Connective tissues are derived from mesoderm and divided into connective tissue proper and
special connective tissue. Connective tissues are composed of widely-spaced cells imbedded in
an extracellular matrix. Loose connective tissues contain cells scattered in an amorphous protein
substance, strengthened by collagen, elastin, or reticulin. Dense connective tissues contain tightly
packed collagen fibers. Regular dense connective tissue, like tendons and ligaments, have
collagen fibers aligned in parallel. Irregular tissue fibers are not regularly oriented and compose
the tissues that cover organs, muscles, nerves, and bones.
The special connective tissues are cartilage, bone, and blood. Each has unique cells and
extracellular matrix allowing specialized function. Cartilage is composed of collagen fibers
interspersed with living chondrocyte cells. Bone is composed of cartilage fibers coated with
calcium salts. Even though embedded in a calcium matrix, the osteocytes remain alive.
New bone is formed by osteoblast cells in concentric layers around nerve and blood vesselcontaining Haversian canals. Numerous types of cells are found within the liquid matrix of the
blood. They include erythrocytes (red cells), leukocytes (white cells), and thrombocytes
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(platelets). There are several types of white cells: neutrophils, eosinophils, and basophils are
named by their special affinity to biological stains. Monocytes and macrophages are phagocytes,
while lymphocytes comprise an important part of the immune system. All types of connective
tissue are similar in their composition of abundant matrix as well as the cell nomenclature
of -blast and -cyte.
Muscle tissue is also derived from mesoderm and exhibits the unique function of contractibility.
These cells possess a great concentration of actin and myosin containing myofibrils. There are
three general types of muscles, categorized by their location and cellular structure. Smooth
muscle cells surround various internal organs and are composed of uninucleate spindle-shaped
cells. Two types of contractions occur in smooth muscle. Muscles lining blood vessels and those
in the iris of the eye contract with nerve stimulation. Other smooth muscles, like those in the
walls of the digestive tract contract spontaneously. Nerves simply regulate their activity. Skeletal
muscle connects bones to one another and underlies the skin. It is composed of multinucleate
fibers produced by the fusion of many individual cells. These cells contract only when stimulated
by nerves. Cardiac muscle is found in the heart and is composed of specially arranged striated
muscle fibers. Certain cells in the myocardium generate a spontaneous electrical impulse which
causes all cells in the myocardium to contract in unison. Nerve tissue is composed of neurons
and supporting cells. An individual neuron is composed of a processing cell body, receiving
dendrites, and a transmitting axon. They are capable of conducting an electrical current and
thereby transmit information. The brain and spinal cord comprise the central nervous system
(CNS) while nerves and ganglia make up the peripheral nervous system (PNS).
Animals possess three types of skeletons. Hydrostatic skeletons, found in soft-bodied
invertebrates, are fluid-filled cavities surrounded by muscle fibers. Exoskeletons are hard,
chitinous cases that surround the bodies of arthropods. Vertebrates and echinoderms possess
endoskeletons in which muscles are attached to a rigid internal skeleton. The human body is
composed of 206 bones divided into the appendicular skeleton (limbs, pectoral, and pelvic
girdles) and the axial skeleton (skull, backbone, and ribcage). Joints permit flexible range of
motions determined by the type of joint. Bones connect to one another at immovable, slightly
movable, or freely movable joints and are connected to muscles via cartilaginous tendons.
Skeletal muscles provide movement in vertebrate organisms. Synergistic muscles work together
to cause movement while antagonistic muscles oppose each other, moving a bone in opposite
directions.
Vertebrate skeletal muscle cells contain a great number of muscle fibers that are the key to their
ability to contract. The cytoplasm of this fiber is called sarcoplasm; the central myofibrils are
constructed of repeating sarcomere units. An individual sarcomere consists of Z lines to which
actin filaments are attached. The actin filaments do not reach completely from one Z line to the
next, the gap is bridged by myosin filaments. Both ends of a myosin filament move
simultaneously, pull the Z lines together, and shorten the sarcomere. Synchronous contraction of
all sarcomeres within a myofibril shortens the entire myofibril. Uniform contraction of all of the
myofibrils results in compression of the entire muscle. On a molecular level, muscle contraction
occurs when the myosin heads form cross-bridges with the actin fibers, each requiring the
expenditure of one ATP molecule.
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Calcium plays an integral role in the control of muscle contraction. The myosin heads are
normally bound by tropomyosin held in place by troponin molecules. Calcium alters the shape of
the troponin molecules, which repositions the tropomyosin away from the myosin. Only then can
the myosin heads bind to the actin filaments, resulting in muscle shortening. Vertebrate skeletal
muscle contraction is initiated by impulses from nerves. A neuromuscular junction occurs where
a nerve innervates a muscle fiber. Stimulation of the motor neuron causes the release of
acetylcholine which causes the muscle fiber to initiate its own electrical impulses. Those
impulses are carried to the T tubules and the sarcoplasmic reticulum, which results in the release
of calcium and shortening of the muscle fibers. When the stimulus stops, the calcium is taken
back up by the sarcoplasmic reticulum and the fibers relax. This entire process is called
excitation-contraction coupling. Whole units of muscle tissue contract smoothly because of the
recruitment of muscle fibers within a motor unit
A twitch is a single brief contraction of a muscle. A second impulse immediately after the first
causes summation as the contraction adds to that of the first. Tetanus results when there is no
visible relaxation between twitches and there is a smooth, sustained muscle contraction. Skeletal
muscle is composed of two distinctly different types of fibers. Type I fibers, also called slowtwitch fibers, require a substantial length of time (in milliseconds) to reach maximum tension. As
expected, type II or fast-twitch fibers, reach maximum tension in just a few milliseconds. Slowtwitch fibers have substantial resistance to fatigue and have a high capacity for aerobic
respiration. They have a rich capillary supply, numerous mitochondria, and a high concentration
of myoglobin to improve delivery of oxygen. Fast-twitch fibers have fewer capillaries and
mitochondria and are better adapted to respire anaerobically due to high concentrations of
glycolytic enzymes.
Animals are mobile organisms that have evolved the ability to move in water, on land, and in the
air. Many aquatic animals move through the water through undulations of their bodies against the
water. Other animals use the same locomotor actions to swim as they would to walk on land.
Terrestrial animals exhibit particular walking gaits depending on the number of legs that they
possess. In general, tetrapods are capable of speedier movement on land than arthropods. Only
four groups of animals have evolved flight. In all of them, propulsion is achieved as the wings
press downward against the air.
LEARNING OUTCOMES
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Understand how vertebrate cells are organized into tissues, organs, and organ systems and give
examples of each.
Describe the general characteristics and functions of epithelial tissue.
Indicate the two classes and three subdivisions into which epithelial tissue is divided and give
examples of each.
Differentiate between exocrine and endocrine glands.
Understand the composition and function of loose versus dense connective tissue.
Describe the specialized connective tissues.
Explain how cartilage and bone are related and the structural advantages of each.
Understand the basic structure of bone tissue and how it is formed.
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Describe and characterize the cellular and non-cellular components of blood.
List 2 similarities of all connective tissue types.
Differentiate among smooth, striated, and cardiac muscle in terms of derivation, location, and
initiation of contraction.
Understand the functional specialization of nervous tissue and how it relates to the anatomy of an
individual neuron.
Characterize the three different kinds of animal skeletons.
Identify the primary components of the axial and appendicular skeletons.
Know the three types of joints and give an example of each.
Differentiate between synergistic and antagonistic sets of muscles.
Understand the microscopic anatomy of skeletal muscle and how it results in movement in the
vertebrates.
Explain the molecular aspects of muscle contraction as it relates to myofilaments, actin, and
myosin.
Understand the effects of calcium on muscle contraction.
Understand how the nervous and muscular systems interact to produce movement.
Understand how twitch, summation, and tetanus affect forceful muscle contractions.
Compare slow-twitch and fast-twitch muscle fibers.
Differentiate among skeletal, cardiac, and smooth muscle tissue with respect to form and
function.
Compare locomotion of animals through water, over land, and in the air.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 43 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.
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Students do not understand the evolution of endosymbionts in animal cells
Students are unsure that many of the lower animals are classified as animals
Students think that all animals evolved at about the same time
Students believe that most animals do not feel pain
Students believe that animals can sense emotions and danger
Students believe that only humans have a well-developed body regulation
Students believe that animals are purely instinctual
Students believe that most animals are vertebrates
Students do not equate humans with being animals
Students believe that all animals have identical organ system structures
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Compare the organization of the human body to (organs). These are then combined to form
entire the construction of a house. The screws, nails, rooms (organ systems) that finally comprise
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the wood, glass, and pipes (tissues) combine to make whole house (the body). interior walls,
ceilings, floors, and windows
Discuss bone healing associated with electrical currents which speed bone growth along natural
stress lines. Exercise has an effect on bone growth as indicated by the diameter of a pitcher’s
pitching versus non-pitching arm. It may also help combat bone deterioration that occurs with
age and osteoporosis. Discuss the physiology of muscular dystrophy, myasthenia gravis, and/or
atrophy of unused muscles. Discuss the physiology of loss of bone density in astronauts.
Myosin and actin are not simply interdigitated, illustrated by interposing the fingers of the left
and right hand with each set of fingers representing a protein. Rather, the fingers of both hands
are actin, adding myosin is like holding short pencils between your fingers when they are placed
tip to tip. As contraction proceeds, your finger tips get closer together, as do your hands
(representing the Z lines).
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 43.
Application
Analysis
Synthesis
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Have students describe the how the digestive system works together with
the nervous system.
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Have students describe the how the muscles work together with the
skeletal system.
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Ask students to explain the benefits separating body functions into
anatomically distinct systems.
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Have students explain the similarities and difference of muscle and nerve
tissue.
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Have students explain why respiratory systems of animals have a high
degree of variation compared to other organ systems.
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Ask students to use organ system anatomy to explain the evidence
supporting a common ancestor for protostomes and deuterostomes.
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Ask students explain how evolution of the vertebral column impacted the
anatomical features of the nervous system.
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Have students design an experiment to test the effectiveness of epithelium
on forming a barrier against the spread of bacteria.
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Evaluation
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Ask the students to find a medical application for knowledge that all
vertebrates use identical proteins to synthesize connective tissues.
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Ask students evaluate the claim the vertebrates are less evolved than
insects.
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Ask students to evaluate the accuracy of studying chicken eggs to get a
better understanding of human organ system formation during
embryological development.
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Ask students to evaluate the effectiveness and safety using medications
that regulate the activities of antagonistic effectors.
VISUAL RESOURCES
Obtain a number of animal organs to illustrate how they are made up of various tissues. Samples
from the grocery are best, but in very large classes they may be substituted with photographs.
Bring in examples of bone and muscle tissue, readily obtained at the local meat market. Ask the
butcher to bisect a long bone in both directions to show the internal structure.
Place a pencil (actin) on a smooth surface (even the overhead projector) “walk” your fingers
(myosin heads) along its length so that it moves backward under your fingers.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Virtual Histology
Introduction
This demonstration permits the class to see histological sections of animal organ systems
mentioned in this chapter. It can be used to demonstrate form and function in tissues and cellular
organization.
Materials
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Computer with Media Player and Internet access
LCD hooked up to computer
Web browser linked to LUMEN at
http://www.meddean.luc.edu/lumen/MedEd/HISTO/frames/histo_frames.html.
Procedure & Inquiry
1. Ask the class if they can recognize the function of a tissue by looking at its cellular
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2.
3.
4.
5.
organization.
Load up the Lumen website.
Then click on a tissue category and show the images to the students.
Then ask the class to determine the function of the tissue in animal. They should justify
their answers and explain the characteristics that determine the function.
Repeat this for the major tissue and cell types of vertebrates.
USEFUL INTERNET RESOURCES
1. Images of animals are available from the University of California at Berkeley CalPhotos:
Animal website. These images are valuable teaching resources for lecture and laboratory
sessions. The site is available at http://calphotos.berkeley.edu/fauna/.
2. Cell and tissue form and function can be reviewed using specialized photomicrographs. A
variety of images that supplement Chapter 43 are available at the Molecular Expressions
Photo Gallery. The website can be found at
http://micro.magnet.fsu.edu/micro/gallery.html.
3. The Cell Centered Database has fluorescent imaging photographs of many animal cells.
This images show students how microscopes can be used to determine cell function.
These images are used to determine cell function. The website can be found at
http://ccdb.ucsd.edu/gallery/gallery.htm.
4. Case studies are an effective tool for stimulating interest in a lesson on fungi. The
University of Buffalo has a case study called “A Strange Fish Indeed: The “Kermit to
Kermette? Does the Herbicide Atrazine Feminize Male Frogs?” This case study explores
the unintended side effects of chemicals introduced into the environment, specifically
organic compounds that can act as endocrine disruptors. The case study can be found at
http://www.sciencecases.org/kermit/kermit.asp.
LABORATORY IDEAS
A. Comparative Animal Systems
This activity has students evaluate the differences and similarities of representative
protostome and deuterostome animal organ systems.
a. Explain to students how all animals have a common ancestor and that all animals address
similar survival issues.
b. Tell students that they will be investigating the similarities and differences in two
representative animals: the clamworm, a protostome, and the fish, a deuterostome.
c. Provide students with the following materials
a. Preserved fish specimen
b. Preserved clamworm specimen
c. Dissecting microscope
d. Dissecting equipment
e. Small ruler
d. Instruct the students to describe the following features of while comparing each
organism:
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a. Relative complexity of organ systems
b. Relative size proportion of organ systems
c. Evidence of conservation of organ system structure and function
d. Evidence of organ system specialization
e. Degree of integration of organ systems
e. The students reports should include an explanation of the similarities considering the
great differences in lineage of clamworms and fish.
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students do a lesson do a hands-on program on the animal homeostasis.
2. Have students tutor high school students studying animal anatomy and physiology.
3. Have students volunteer on environmental restoration projects with a local conservation
group.
4. Have students volunteer at the educational center of a zoo or marine park.
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