Download Body Systems - Macmillan/McGraw-Hill

Copyright © 2009 by The McGraw-Hill Companies, Inc. All rights reserved. Except as permitted
under the United States Copyright Act, no part of this publication may be reproduced or distributed
in any form or by any means, or stored in a database or retrieval system, without prior permission
of the publisher.
Send all inquiries to:
Macmillan/McGraw-Hill
8787 Orion Place
Columbus, OH 43240-4027
ISBN: 978-0-02-288023-1
MHID: 0-02-288023-2
Printed in the United States of America.
1 2 3 4 5 6 7 8 9 10 066 13 12 11 10 09 08
Lesson 1
•
Body Systems . . . . . . . . . . . . . . . . . . . . . . 2
Explore Activity: How do body parts work together? . . . . .3
Careers: Careers in Medicine . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Lesson 2
•
Bones, Muscles, and Skin . . . . . . . . . . . . 14
Explore Activity: How do muscles and bones work
together? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Lesson 3
•
Circulatory and Respiratory Systems . 24
Explore Activity: How does air enter and
leave the lungs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
History of Science: Heart Surgery Pioneers . . . . . . . . . . . . . 34
Lesson 4
•
Digestive System . . . . . . . . . . . . . . . . . . 36
Explore Activity: Why is the small intestine full of folds? . .37
Lesson 5
•
Nervous System . . . . . . . . . . . . . . . . . . .44
Explore Activity: Can reaction time change? . . . . . . . . . . . 45
Animal Bodies: Wide Nerves for Giant Squids . . . . . . . . . . 54
Lesson 6
•
Excretory System . . . . . . . . . . . . . . . . . 56
Explore Activity: How do your kidneys filter out waste? . .57
Lesson 7 • Endocrine and Reproductive
Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
Explore Activity: How do emotions affect the body? . . . . 65
Lesson 8
•
The Human Life Cycle . . . . . . . . . . . . . . 72
Explore Activity: How do boys and girls
grow differently? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
Science, Technology, and Society: At the Hospital . . . . . . 80
Lesson 9
•
The Body’s Defenses . . . . . . . . . . . . . . . 82
Explore Activity: How quickly can germs spread? . . . . . . . .83
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
iii
Lesson 1
•
Body Systems . . . . . . . . . . . . . . . . . . . . . . 2
Explore Activity: How do body parts work together? . . . . .3
Careers: Careers in Medicine . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Lesson 2 • Bones, Muscles, and Skin . . . . . . . . . . . 14
Explore Activity: How do muscles and bones work
together? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Lesson 3 • Circulatory and Respiratory Systems . 24
Explore Activity: How does air enter and
leave the lungs? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
History of Science: Heart Surgery Pioneers . . . . . . . . . . . . . 34
Lesson 4
•
Digestive System . . . . . . . . . . . . . . . . . . 36
Explore Activity: Why is the small intestine full of folds? . .37
Lesson 5
•
Nervous System . . . . . . . . . . . . . . . . . . .44
Explore Activity: Can reaction time change? . . . . . . . . . . . 45
Animal Bodies: Wide Nerves for Giant Squids . . . . . . . . . . 54
Lesson 6
•
Excretory System . . . . . . . . . . . . . . . . . 56
Explore Activity: How do your kidneys filter out waste? . .57
Lesson 7 • Endocrine and Reproductive
Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
Explore Activity: How do emotions affect the body? . . . . 65
Lesson 8
•
The Human Life Cycle . . . . . . . . . . . . . . 72
Explore Activity: How do boys and girls
grow differently? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
Science, Technology, and Society: At the Hospital . . . . . . 80
Lesson 9
•
The Body’s Defenses . . . . . . . . . . . . . . . 82
Explore Activity: How quickly can germs spread? . . . . . . . .83
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
iii
Lesson 1
Body Systems
Pulling on a string will control a kite. How do
you control your arms, legs, and other body
parts? Do you think your body uses anything
similar to kite strings?
2
ENGAGE
Materials
How do body parts work
together?
Purpose
Explore how body parts and body systems can work
together, even when doing very simple tasks.
What to Do
Work with a partner. Ask your partner to think of
instructions for you to use your muscles, such as
“Hop on one foot” or “Make circles with your arms.”
• stopwatch or timer
• pencil
• paper
Experiment Have your partner call out the
instructions. Follow them as best you can. Have
your partner time you for 1 minute. Tell your
partner how you feel as you use your muscles.
Stop after 1 minute or when you feel tired.
Step
Communicate List the different body parts that
you used during step 2. Include the parts that you
used for hearing and understanding the activity.
Also discuss any changes you observed in your
body and the parts that the changes affected.
Record your responses.
Switch roles with your partner, and repeat steps 2
and 3.
Draw Conclusions
Classify For each body part you listed in step 3,
describe the job it performed. Classify the parts
according to their jobs.
Infer Could you keep moving your body all day
long? Why or why not?
Predict What would happen to the human body
if its body parts did not communicate with one
another?
Explore More
Choose a body part that you can observe easily, such
as the shoulder, wrist, ankle, or foot. Observe and
record the ways you use this part throughout the day.
3
EXPLORE
How does the body meet its
needs?
▶ Main Idea
Organ systems work
together to maintain cells
and to keep the body
healthy and active.
▶ Vocabulary
cell, p. 4
glucose, p. 4
organ system, p. 6
hormone, p.6
What is the most important thing you will do
today? “Breathe” may not have been the first answer
that came to mind, but think about how hard it is to
hold your breath for more than a few seconds.
Whether or not you pay attention to breathing, it is
extremely important. If you were not able to keep
breathing, you would survive for only a few minutes.
Why must you breathe, and breathe so often? Just
what does the human body do with all that air? The
answers involve the needs of the tiny parts that make
up the body. These parts are your cells.
The body is made of trillions of living cells. Like the
cells of any animal, each cell of the human body needs
to take in certain substances and carry out certain
processes to stay alive.
Food Every cell needs materials that food provides.
The digestive system breaks down foods into these
materials, then blood carries them to the body’s cells.
Glucose (GLOO•kohs) is a type of sugar that cells use
for energy. Many foods are broken down into glucose.
Oxygen Cells need oxygen to break down glucose
and capture its energy. The lungs supply oxygen to the
blood, and then the blood carries it to cells. The body
must keep breathing because cells use oxygen very
quickly, and they cannot store it.
Water Did you know that water makes up most of
the human body? As water is used by cells, it must be
replaced. This is why you should drink plenty of
liquids—such as water, juice, or milk—every day.
◀ Body cells use food and
oxygen to meet their need
for energy. The body is
organized to meet the needs
of every cell.
4
EXPLAIN
Blood Cells as Carriers
food,
oxygen,
and water
blood cells
energy
carbon
dioxide and
other wastes
▲ Cells use the energy from
food to do different jobs for
the body.
▲ Blood provides the food,
oxygen, and water that body
cells need, and it carries
away the wastes.
Read a Diagram
Why do body cells need to be near
a blood supply?
Waste Removal As cells break down
glucose, they make a waste gas called
carbon dioxide. The blood carries carbon
dioxide to the lungs, where it is breathed
out. Blood also carries away other waste
products of cells.
Muscle cells use energy to move. Muscle
cells cannot move from place to place in
the body, but they can get longer or
shorter. By working together, many muscle
cells pull on bones that are joined to them,
moving arms, legs, and other parts.
Communication The body could not
function if its trillions of cells each acted
on their own. Communication among cells
allows the body to carry out coordinated,
complex tasks. These tasks include growth
and movement.
Red blood cells work as carriers. They
carry oxygen to and carbon dioxide from
cells. White blood cells work as protectors.
They fight bacteria and other germs that
could harm the body.
Jobs for Cells
All cells gets energy from food and
oxygen. They use the energy to do different
jobs. Some cells make special products. For
example, certain cells in the stomach make
an acid that helps break apart food. Cells
in the liver make bile, a thick liquid that
helps break up fats in food.
Other cells act as messengers. A nerve
cell might signal a muscle to tighten or
relax. Or it might carry information from
the eyes, ears, or other sense organs to the
brain. Blood also carries messages from
one cell to another.
The cells of the body do all these jobs
and many others.
Quick Check
Critical Thinking Why does your body
need to breathe?
5
EXPLAIN
Organ Systems
To meet the needs of its cells,
the human body is organized into
organ systems. An organ system is
a set of body parts, called organs,
that work together to complete a
task. In humans, organ systems are
also called body systems.
Many organ systems work all
the time; others work only when
the need arises. All organ systems
work together to keep the body
healthy and active.
Quick Check
Critical Thinking How are
different body systems related?
Excretory
Organs: kidneys and
urinary system, end
of the digestive
tract, lungs, skin
Respiratory
Organs: mouth and
nose, air tubes, lungs
Job: breathing, which
brings oxygen in and
takes carbon dioxide
out of the blood
Immune
Organs: lymph nodes
and ducts, spleen,
thymus (THIGH•muhs),
and other organs
Endocrine
Organs: glands in the
head, neck, and
elsewhere
Job: making hormones,
which are chemical
messengers that travel
through the blood
Reproductive
Organs: ovaries in
women, testes in men,
and other organs
Job: reproducing
Job: removing wastes
from the body
6
EXPLAIN
Job: stopping bacteria
and other agents
of disease
Digestive
Organs: mouth,
esophagus
(i•SO•fuh•guhs),
stomach, intestines,
and many glands
Job: digestion, or
the breaking down
of food into pieces
the body can use
Skeletal
Nervous
Organs: brain, spinal
cord, nerves, sense
organs
Job: controlling other
body systems; sensing
and responding to the
environment; thinking
and remembering
Muscular
Circulatory
Organs: heart, blood
vessels
Job: bringing blood to
every cell of the body
Integumentary
Organs: bones and
other hard tissues
Organs: muscles
and tendons
Organs: skin, hair, and
nails
Job: supporting and
protecting the body;
allowing it to move
at joints
Job: moving bones
and other organs
Job: covering and
protecting the body
7
EXPLAIN
Systems Working Together
None of the organ systems of the body
could work on its own. Each depends on
the other organ systems to do its job. They
all work together to perform even simple
tasks.
For example, your teacher might give
you a set of instructions. The instructions
are to go to your desk, find a pencil and a
piece of paper, and write the name of your
first pet.
Under the guidance from another part of
your brain, your muscular and skeletal
systems moved your body in just the right
way so you could get to your desk. They
also allowed you to grasp a pencil and
write with it. In addition, your circulatory
and respiratory systems were working to
bring glucose and oxygen to all of your
body parts so that they could carry out
their functions.
These five organ systems work together
whenever you need to perform a task.
Completing this task involves at least
Often a sixth system joins them. Your body
five organ systems. Your nervous system
needs different amounts of glucose
signaled the nerves in your eyes and parts
depending on whether you are exercising,
of your brain to read the instructions, to
resting, or sleeping. Hormones produced by
remember where your desk is located, and
the endocrine (EN•duh•kruhn) system help
to search for a pencil and paper. Meanwhile manage glucose levels to meet the body’s
your brain remembered the name of your
changing energy needs. Your endocrine
pet, as well as the spelling of that name.
system responds to your activity level.
The endocrine system helps
other systems work together
to meet the body’s needs.▼
8
EXPLAIN
Keeping Healthy
When the body is healthy, every body
system works properly. But if a part
breaks in one system, other systems could
be affected.
Body systems communicate their needs
through the nervous system. Feelings of
hunger, thirst, and tiredness all tell the
brain to take action in a way that helps
the body.
Even pain is useful. Pain signals the
brain that a body part is injured and
needs help. In mild cases, such as a
stubbed toe, resting the body part is all
that is needed. In cases of severe pain that
does not improve, help from a health-care
expert might be necessary.
Ways to stay healthy include
exercising and eating a balanced diet.
Exercising helps maintain the body at a
healthy weight. It strengthens bones and
muscles, and it improves sleep. Exercising
can even help the mind! It increases
blood flow to the brain and stimulates
the production of hormones that improve
mood. Activities that increase the heart
rate, such as jogging, may help people
feel happier and remember things better.
Ad Review
What to Do
People buy many products to improve
their health or keep them safe. Find ads
for these products in old magazines and
newspapers.
Classify Present the ads to the class.
Group them according to the body
systems they help or protect.
Evaluate Explain how the ads try to get
people to buy the products. Identify ads
that you think are effective.
Draw Conclusions
Infer Why might people buy health and
safety products they do not need?
Discuss.
If you have questions about your
health or your body, you can ask your
parents, your teacher, or a doctor, nurse,
or other health expert. Your body must
last a lifetime, so care for it wisely!
Daily exercise is an important
key to healthy living. ▶
Quick Check
Critical Thinking Why must body
systems work together?
9
EXPLAIN
Studying the Body
How have scientists learned so much about organs and
organ systems? When you visit a doctor, how can he or she
learn what is happening inside you? The answers to these
questions involve medical technology—tools for studying and
treating the human body. Doctors also depend on science skills,
such as observing, inferring, and drawing conclusions.
Quick Check
Draw Conclusions When might a doctor choose each of the
technologies shown here?
Medical Technology
Microscope Scientists have studied cells from every body organ.
By looking through a microscope, they can tell if a cell is normal or
damaged. They also can spot invaders, such as germs, as well as
diseases, such as cancer.
X-ray Skin and other soft body parts let X-rays pass through them.
But bones and teeth block X-rays, so they leave shadows on an
X-ray picture. To picture the heart or blood vessels, a special dye
is injected into the patient. The dye blocks X-rays much like hard
body parts do.
MRI Unlike X-rays, a technique called MRI can take a detailed
picture of any body part. The three letters stand for magnetic
resonance imaging. An MRI uses the body’s atoms and molecules to
show internal body parts in great detail. The technique uses
powerful magnets, a special dye, and a computer.
Stethoscope Doctors use stethoscopes to listen to the body’s
internal sounds. The heart, lungs, and intestines all make sounds,
and each sound is a clue to how well an organ is working. Many
doctors would say that the stethoscope is one of the most
important tools they use.
10
EXPLAIN
Visual Summary
The body is made of
trillions of cells. Each
cell needs food,
including glucose for
energy. Cells also
need oxygen, water,
and waste removal.
An organ system is a
group of organs that
work together to
complete a task.
These tasks include
circulating blood,
digesting food, and
moving the body.
Organ systems work
closely together.
Bones and muscles
work together to
move the body.
Organ systems
respond to meet the
body’s changing
needs. The nervous
and endocrine
systems act as
coordinators and
messengers.
Writing Link
Think, Talk, and Write
Main Idea How does the body meet
all of its cells’ needs?
Vocabulary A chemical messenger
called a(n) ______ travels through the
blood from one cell to another.
Classify List three examples of your
body acting automatically. List three
examples of your body acting from
your thoughts.
Critical Thinking Why is rapid
communication important in the body?
Give an example to support your
answer.
Test Prep The kidneys, skin, and
lungs are each a part of the
respiratory system.
excretory system.
integumentary system.
nervous system.
A
B
C
D
Test Prep Cells of the immune system
act as _______ for the body.
A carpenters
B special-delivery messengers
C protectors
D clean-up crews
Social Studies Link
Write an Essay
History Report
How are the cells of the human body
like a single-celled organism? How are
they different? Write an essay that
compares and contrasts these two
types of cells.
Research an event or discovery from
the history of medicine. Examples
include the work of Joseph Lister, Louis
Pasteur, Marie Curie, or Charles Drew.
Share your report with the class.
11
EVALUATE
Careers in
Medicine
Physician
Physicians (fuh•ZI•shuhnz), or medical
doctors, are experts on the human
body. They are the leaders of the
health-care team.
Physicians study every body system and
the common diseases that affect them. Yet
many physicians are specialists, meaning
they treat only certain kinds of illnesses. A
cardiologist treats heart diseases. A
neurologist treats diseases of the nervous
system. Some doctors specialize in certain
kinds of patients. For example,
pediatricians treat children.
Most physicians see patients in the
hospital, in private offices, or at clinics.
Some physicians research cures for serious
diseases, such as cancer and AIDS. Many
work to bring good health care to
communities that need it.
To be a physician, a person must usually
study for 4 years in college, then for 4
years in medical school. In order to
specialize in a certain area, a physician
must often have an additional year or two
of training.
▲ Communicating with
patients is an important
part of a physician’s job.
12
EXTEND
Careers
Physical Therapist
When you were a baby, your body
learned how to use the muscles in your
legs, arms, and other body parts. Even now
you are learning new ways to move.
You practice these movements when
you play sports, study a musical
instrument, or learn a dance step.
A physical therapist may work with
patients for weeks or even months to
help them regain lost movement. ▼
However, people sometimes lose
the use of muscles and body parts,
either partially or totally. The cause
could be a broken bone, a genetic
disorder, or an injury to the nervous
system.
Recovering from serious injuries
and diseases takes time and effort. In
many cases, physical therapists can
help. They might lead a patient in
exercises that retrain the body to use
a non-working part. Or they may
help patients find new ways to move
their bodies.
Physical therapists must earn a
degree and a license. Many work in
hospitals or doctors’ offices. Others
work in offices of their own.
Write About It
Research How do physical
therapists do their job? What
equipment do they use? Research
physical therapists and create a
catalog of the different pieces
of equipment they might use.
Be sure to include what each
piece of equipment is used for.
13
EXTEND
Lesson 2
Bones, Muscles,
and Skin
In ancient times running fast helped people catch
food and escape danger. Today people run fast
in races. What body parts work together to help
you run?
14
ENGAGE
Materials
How do muscles and bones work
together?
Form a Hypothesis
Muscles work in pairs to move bones. What would
happen if one muscle in a pair stopped working?
Write your answer as a hypothesis in the form “If one
muscle failed, then….”
• 2 cardboard strips,
each 30 cm long
Test Your Hypothesis
Make a Model Punch a hole near the end of each
• string
cardboard strip. Put the brass fastener through
the holes to fasten the two strips together. Tape
pieces of string to the model and add a paper
hand to the end of one strip as shown.
• hole punch
• brass fastener
• tape
• paper hand cutout
Observe Place the model arm flat on the desk.
Hold the end that would attach to the shoulder.
Pull the strings one at a time. Observe the motion
of the arm.
Remove one string, and then pull the string that
remains. Describe how the arm’s range of motion
has changed.
Experiment Move the remaining string to other
positions along the arm. Pull the string, and
compare the results to those from step 2.
Step
hold here
pull
pull
Draw Conclusions
Infer What do the strings and
cardboard represent in your model?
Interpret Data Did the results support your
hypothesis about muscles? Explain.
Predict If one muscle that crossed an elbow
stopped working, predict what would happen to
the elbow.
Explore More
Choose a pair of bones or a joint in the body that
moves differently than the elbow. Build a model of it.
How does your model compare to the elbow model?
15
EXPLORE
What are the bones of the body?
▶ Main Idea
Systems of bones,
muscles, and skin protect,
support, and move the
body.
▶ Vocabulary
cartilage, p. 16
skeletal system, p. 16
joint, p. 18
ligament, p. 18
muscular system, p. 20
dermis, p. 22
epidermis, p. 22
Compare the top of your head to your nose and your
ears. The skull is made of hard bone. Parts of the nose
and ears are made of a softer material called cartilage
(KAHR•tuh•lij). Cartilage is also found at the ends of
many bones and in tubes that carry air to the lungs.
The adult skeleton has 206 bones. Bones and
cartilage make up the skeletal system. This system
supports, protects, and gives shape to your body. It also
works with the muscular system to move your body.
Skull The skull is a set of more than 20 bones, most
joined tightly together. The skull surrounds the brain,
protecting this delicate organ.
Three tiny bones make up the middle ear: the
hammer, the anvil, and the stirrup. They have
important roles in hearing.
Spine The spine runs down the center of the back. It is
made of separate bones called vertebrae (VUHR•tuh•bray).
The spine surrounds and protects a set of nerves called
the spinal cord. It also supports the entire body,
allowing it to stand upright.
Ribs and Sternum Twelve pairs of ribs are attached to
the spine and wrap around the body. Most ribs connect
to a flat bone called the sternum. Together they protect
the heart, lungs, and other organs of the chest.
Collar, Shoulder, and Hip Bones These bones have
curved shapes. They support the arms and legs,
allowing them to move freely.
Arm and Leg Bones The arm and the leg each
contain one long bone in the upper half of the limb and
two long bones in the lower half. Both the hands and
the feet contain many small bones.
Quick Check
▲ A helmet acts like an extra
skull. Both help protect the
brain, a very important organ.
16
EXPLAIN
Critical Thinking Why is it useful for the skeletal
system to have a wide variety of bones?
Bones of the Skeletal System
skull
mandible (jaw)
clavicle (collarbone)
humerus
ribs
radius
vertebrae
pelvis
femur
patella
tibia
Read a Diagram
What clues do bones provide about
the body parts around them?
17
EXPLAIN
Types of Joints
Joints
The human body can move because of
its joints (joynts). Joints are the places
where two or more bones meet. The body
uses many types of joints, each allowing a
different range of motion. Many joints are
held together by ligaments (LI•guh•muhnts),
which are tough, ropelike tissues.
A ball-and-socket joint allows movement
backward, forward, and side-to-side.
These joints are found in the shoulders
and hips.
Some joints cannot move. These are
called immovable joints. For example, the
joints among the many bones that make up
an adult’s skull are tightly woven together.
The joints between vertebrae move only
slightly. This movement allows the back to
arch, but not to bend at a sharp angle.
Inside these joints are cushionlike discs.
They absorb any up-and-down forces on
the spine. They allow the body to walk,
run, and jump with ease.
Free-moving joints allow body parts to
bend or twist. Inside each of these joints is
a space filled with fluid.
A hinge joint allows backward and
forward movement, like the hinge of a
door. These joints are found in the elbow,
knee, fingers, and spine.
When a joint is moved beyond its limits,
ligaments may tear, twist, or break. This
is called a sprain. Sprains often take a
long time to heal.
▼ Joints in the arm,
shoulder, and neck
are all different,
but they all allow
for movement.
A saddle joint allows movement
backward, forward, and side-to-side, but
limited rotation. A saddle joint connects
the thumb to the rest of the hand.
18
EXPLAIN
More About Bones
Bones are hard and tough, yet still light
enough for the body to carry and move.
They are also made of living cells. Blood
vessels bring blood to and from bones, just
as they do for other organs. Nerves travel
to bones, too.
Most bones are made of several layers.
The outside is a thin, hard layer called
compact bone. Underneath is a slightly
softer layer called spongy bone. The centers
of bones are filled with a jellylike tissue
called marrow (MER•oh). Marrow can be
red or yellow. Red marrow makes most of
the body’s blood cells.
Bones form from cartilage. Babies are
born with a mixture of bone tissue and
cartilage in places where adults have only
bones. In children cartilage builds up on the
ends of bones. This cartilage is gradually
replaced by bone tissue over time, making
the bones longer and harder. This process
continues until just after the teenage years.
When the cartilage stops building on the
bones, the bones stop growing longer. At
this time the body stops growing taller.
Bone tissue is constantly being broken
down and rebuilt. This process helps heal
bones when they break.
Quick Check
Critical Thinking How is bone tissue
more useful in the body than steel or
strong plastic would be?
Inside a Bone
compact bone
spongy bone
bone marrow
◀ A cast helps a broken
bone to heal properly.
The two broken ends
of the bone must
meet exactly.
19
EXPLAIN
Muscles
Bones and other body parts are attached
to organs called muscles. All the muscles
make up the muscular system, which
moves the body. It also helps keep the body
in balance, allowing it to stand up straight
and hold other positions.
There are three types of muscle: skeletal,
smooth, and cardiac. Although the brain
controls every muscle, only the skeletal
muscles’ movements are voluntary. This
means that the brain decides when and how
to move them. Other muscles’ movements
are involuntary. The brain controls them
automatically.
Most skeletal muscle attaches to bones
with tendons (TEN•duhnz), which are tough,
cordlike tissues. Ligaments hold tendons
and bones in place.
The fibers that make up skeletal muscle
are organized to contract, or shorten, but
they only exert force in one direction. They
can only pull on bones. They do not push
them. For these reasons, most bones are
moved by pairs of muscles. When one
muscle contracts, the other relaxes. This
causes movement.
▲ With practice, muscles can move
the body in amazing ways. They
also become stronger with exercise.
Working muscles use a lot of energy.
They depend on the circulatory system to
bring glucose and oxygen to them. Muscles
also store glucose, which they break down
when energy is needed.
Muscle Types
Skeletal muscle
• moves bones
• voluntarily controlled
• has striped cell structure
20
EXPLAIN
Smooth muscle
• moves the intestines,
stomach, and other organs
• automatically controlled
• has no stripes in cells
Cardiac muscle
• pumps the heart
• automatically controlled
• has striped cell structure
that differs from
skeletal muscles
Working Together
A typical pair of skeletal muscles crosses
a joint on two sides. For example, the
biceps muscle crosses over the elbow, and
the triceps muscle crosses below it.
When the biceps muscle contracts, the
elbow bends to make a smaller angle,
bringing the hand toward the shoulder. This
motion is called flexing. When the triceps
muscle contracts, the angle widens. This
motion is called extending.
Under the brain’s control, the biceps and
triceps work together to flex and extend the
elbow. Your muscles and brain learned how
to do this when you were a baby. Now
when you decide to flex or extend your
elbow, the brain sends exactly the right
signals to make it happen.
triceps muscle
contracted
Muscle Model
Muscle tissue is made of many fibers. The
fibers never shorten, so why does the
muscle shorten? Form a hypothesis, and
then test it with a model.
Materials: 3 pencils of equal size
What to Do
Make a Model Hold the pencils
between the fingers of both hands as
shown. A partner may help you
position them.
Slowly move your hands together
along the pencils. This models how a
muscle contracts.
Draw Conclusions
Does the model support your
hypothesis? Explain.
Pairs of muscles work to bend joints
all over the body. As a general rule, the
largest, thickest muscles move the heaviest
body parts, such as the legs and upper
arms. Thin, delicate muscles move the
fingers and toes. Even the eyes use
muscles to move. A set of muscles rotates
an eyeball up, down, left, and right.
biceps muscle
contracted
Quick Check
Critical Thinking Why must muscles
work in pairs to move a bone at a joint?
21
EXPLAIN
The Skin
What is the body’s largest organ? It’s the
organ on the outside—the skin. The skin
separates and protects the internal organs
and tissues from everything outside. Nerves
that end in the skin sense pain, touch, and
temperature. Certain skin cells use sunlight
to make vitamin D. Oils in the skin keep it
soft and flexible.
The skin has two layers. The inner layer
is the dermis (DUHR•muhs). The dermis
contains blood vessels, nerves, glands, and
hair follicles. The outer layer is the
epidermis (e•puh•DUHR•muhs).
Skin is part of the integumentary system.
This body system also includes hair,
fingernails, and toenails. Both hair and
nails are made of a tough material called
keratin (KER•uh•tuhn). Nerves and blood do
not travel into hair and nails, which is why
haircuts and nail filing are not painful.
Skin is also part of the excretory system.
When the body gets hot, sweat glands in
the skin release a salty liquid called sweat.
This cools the skin as the water in the
sweat evaporates.
Skin cells divide rapidly on the inner
edge of the epidermis and are pushed to the
outside. Eventually the cells die and flake
away. The body loses about 35,000 skin
cells every minute!
Quick Check
Critical Thinking Why is blood needed
in the dermis but not in the outer cells of
the epidermis?
▼ Skin is made of layers of cells.
Hair, sweat, and oils all come from
the inner layer, the dermis.
oil gland
epidermis
nerves
dermis
hair follicle
blood vessels
22
EXPLAIN
sweat gland
Visual Summary
The skeletal system
provides a framework
to support and
protect the body. It is
made of bone and
cartilage.
Bones meet at joints.
Some joints do not
move. Others move
partially or freely.
Think, Talk, and Write
Main Idea What are the jobs of
muscles, bones, and skin?
Vocabulary Tough tissues called
______ hold bones in place.
Cause and Effect The brain controls
smooth and skeletal muscles in
different ways. How does this
difference help the body work?
Cause
Effect
Critical Thinking The human arm has
The muscular system
uses three types of
muscles: skeletal,
smooth, and cardiac.
Skeletal muscles are
the only type with
voluntary movement.
The dermis is the
inner layer of the skin
and is made of living
cells. The epidermis is
the outer layer. It
sheds dead cells.
Writing Link
30 bones, but 27 of them are in the
hand and wrist. What does this explain
about the way arms and hands work?
Test Prep Where in the skeletal
system are blood cells made?
A cartilage
B hair
C fluid inside joints
D red bone marrow
Test Prep Sweat glands, hair follicles,
blood vessels, and nerve endings are
found in
A bones.
B muscles.
C the dermis.
D the epidermis.
Math Link
Research Report
Count Skin Cells
Research scoliosis, a condition in which
the spine is unusually curved. In your
report discuss its causes, effects,
and treatments.
The body loses 35,000 dead skin cells
every minute. Calculate how many skin
cells it loses in 1 hour, 1 day, and 1 week.
Round each answer to the nearest
million cells.
23
EVALUATE
Lesson 3
Circulatory and
Respiratory Systems
Your lungs have millions of these tiny air sacs.
What force pulls air into them? What force
pushes air out?
24
ENGAGE
Materials
How does air enter and leave
the lungs?
Make a Prediction
Your body gets the oxygen it needs from air. How is
air moved into and out of the lungs? Make a
prediction.
Test Your Prediction
• plastic bottle with
its bottom cut off
Make a Model Use a rubber band to attach the
• drinking straw
opening of the small balloon to one end of the
straw. The balloon represents the lungs. The straw
represents the airways to the lungs.
• scissors
• small balloon
Insert the straw and balloon into the top of the
bottle. Seal the hole with modeling clay.
• large balloon
Cut open the large balloon. Stretch it across the
open bottom of the bottle. Seal it with a rubber
band or tape.
• modeling clay
• 2 rubber bands
Experiment Pull down slowly on the stretched
balloon, then release it. Observe what happens to
the model lungs. Record your observations.
Step
Draw Conclusions
Compare Muscles act to move the body. Which
part of your model acts like a muscle? What
changes does it cause?
Infer Using your model as a guide, describe how
air moves into and out of the lungs.
Explore More
How does your chest change size as you breathe?
Make a prediction, and design a way to test it.
25
EXPLORE
Why must the body breathe?
▶ Main Idea
The circulatory and
respiratory systems work
together to bring oxygen
to body cells and to take
away carbon dioxide
from them.
▶ Vocabulary
respiratory system, p. 26
alveoli, p. 27
capillary, p. 27
diaphragm, p. 27
circulatory system, p. 28
artery, p. 28
vein, p. 28
hemoglobin, p. 30
Breathing is important for two reasons. First,
breathing takes in oxygen, which cells use to break
apart food to get energy. Second, breathing removes
carbon dioxide, a waste gas from cells.
The body cannot store oxygen or carbon dioxide for
long periods of time. This is why you need to breathe
continuously, even while you are asleep.
Breathing is the job of the respiratory system. The
lungs are the main organs of this system. Other organs
are the airways that lead to the lungs, including the
mouth and the nose.
To and From the Lungs
To inhale is to breathe in. When you inhale, air is
pulled into your lungs. The air travels through your
mouth or nose and then down a stiff tube called the
trachea (TRAY•kee•uh). The trachea is the main tube in
a system of branching air tubes, much like the trunk
and branches of a tree.
The Respiratory System
nose
mouth
The motion of the diaphragm pulls
air through the mouth and nose into
the lungs. It then pushes air back
out along the same path. ▶
lungs
diaphragm
26
EXPLAIN
Near the lungs, the trachea divides into
two tubes called bronchi (BRONG•kigh).
The bronchi branch into smaller tubes that
end in tiny air sacs. These sacs are called
alveoli (al•VEE•uh•ligh). An adult lung has
hundreds of millions of alveoli!
All alveoli are surrounded by capillaries
(KA•puh•ler•eez). A capillary is a short,
narrow blood vessel. In a healthy lung, thin
membranes separate alveoli and capillaries.
Gases pass easily across these membranes.
Oxygen passes from the alveoli into the
blood. Carbon dioxide passes from the
blood into the alveoli.
Carbon dioxide leaves through your
mouth and nose when you exhale, or
breathe out. As you inhale and exhale over
and over, the respiratory system carries out
the cycle of gas exchange.
The Diaphragm
The muscles of the rib cage and the
chest force air in and out of the lungs. The
largest of these muscles is the diaphragm
(DIGH•uh•fram). The diaphragm is the long,
flat muscle beneath the lungs.
When you inhale, your diaphragm
contracts and moves downward. This
makes your chest larger and creates a
vacuum. Air rushes into your lungs to fill
the vacuum.
The opposite process happens when you
exhale. Your diaphragm moves up into the
chest, making your chest smaller. Air is
then pushed out of your lungs.
Quick Check
Critical Thinking What would happen if
a person’s diaphragm were injured?
Gases exchange
between alveoli and
the capillaries that
surround them. ▶
trachea
alveoli
bronchi
Read a Diagram
What path does air follow as
you breathe?
▲ A series of air tubes lead through
the lungs to the alveoli.
27
EXPLAIN
The Circulatory System
To circulate is to move in a circle or
through a cycle. The circulatory system
works to keep blood moving through
all parts of the body. Blood circulates
during times of exercise and times of
rest. It circulates whether the body is
standing up straight, lying flat, or hanging
upside down!
Arteries
carry blood
away from
the heart.
The heart is the main organ of the
circulatory system. The heart acts like a
pump, supplying the power that keeps
blood moving. The heart lies in the center
of the chest, between the lungs. If you
place your hand on the skin above your
heart, you can feel it beating.
Blood vessels are the other organs of
this system. A blood vessel is a tube that
carries blood. The three types of blood
vessels are arteries (AHR•tuh•reez), veins,
and capillaries.
A Path for Blood
Blood may travel in many paths as
it cycles through the body. Yet each
path leads into and out of the heart and
the lungs.
Blood that leaves body cells is low in
oxygen and high in carbon dioxide. It
gathers in the veins that lead to a heart
chamber called the right atrium. Next
blood passes to the right ventricle, which
pumps it to the lungs.
Veins carry
blood back to
the heart.
Key:
Oxygen-rich blood
Oxygen-poor blood
28
EXPLAIN
Capillaries
connect
arteries and
veins. Gases,
food, and
wastes travel
back and forth
through the
capillary walls.
The Heart
The heart is a twosided pump. The right
side pumps blood to
the lungs. The left side
pumps blood to the
rest of the body.
aorta
pulmonary artery
3
1
Oxygen-rich blood
from the lungs enters
the left atrium.
Oxygen-poor
blood from the
body enters the
right atrium.
4
2
As the left atrium
contracts, oxygenrich blood flows into
the left ventricle. The
blood is pumped to
the rest of the body
through the aorta.
As the right atrium contracts,
oxygen-poor blood flows into
the right ventricle. The blood is
pumped to the lungs through
the pulmonary artery.
Inside the lungs, oxygen moves into the
blood as carbon dioxide leaves. The
oxygen-rich blood then flows back to the
heart, this time to the left side.
The left ventricle pumps this blood into
the aorta (ay•OR•tuh), the body’s widest
artery. Several arteries branch off the aorta.
Many branches lead to the head and arms.
Other branches travel to heart muscles. The
lower part of the aorta leads to the legs.
Arteries continue branching to reach
every body part. As they branch, they get
smaller and smaller. Eventually, they
become capillaries, which are only one cell
thick and very fragile.
The oxygen leaves the blood in the
capillaries and travels to the cells. At the
same time, carbon dioxide and other wastes
move from the cells into the blood inside
the capillaries.
The end of a capillary is joined to a
small, narrow vein. Veins are organized
much like arteries. A huge number of small
veins join to form larger ones, eventually
leading back to the heart.
Quick Check
Critical Thinking How do the two sides
of the heart compare?
29
EXPLAIN
red blood cell
white blood cell
serum
▲ Blood travels to all body parts. It
carries gases, food, proteins, and
clotting agents.
Blood
What is blood? Blood is a movable body
tissue. It is made of many materials,
including cells and parts of cells. The liquid
part of blood is called serum.
Blood does many important jobs,
including carrying gases and other
materials, clotting, and protecting the body
from disease.
Carrying Gases As you know, blood
carries the gases oxygen and carbon
dioxide. Both gases bind to a special
compound in red blood cells called
hemoglobin (HEE•muh•gloh•buhn).
Hemoglobin contains iron and gives these
cells their red color.
Carrying Food, Proteins, and
Wastes Blood serum contains all sorts of
things that cells need, as well as waste
products of cells. From capillaries, serum
leaks out of the blood and moves into the
lymph (limpf).
30
EXPLAIN
Lymph is a pale fluid that surrounds
body cells. It removes cell wastes. Lymph
collects in vessels that are much like blood
vessels. The vessels join together and lead
to lymph nodes, which filter the lymph.
Then the lymph is returned to the blood.
Clotting When blood is exposed to air, it
forms a dry, sticky mass called a clot. A
blood clot stops blood from flowing out of
a wound.
Forming blood clots is the job of blood
proteins and platelets (PLAYT•luhts).
Platelets are small pieces of blood cells. At
the site of a wound, platelets clump
together while blood proteins form sticky
threads. These combine to form a clot.
Fighting Invaders White blood cells
fight invaders, such as bacteria and viruses,
that could make the body unhealthy. The
blood carries many kinds of white blood
cells, each of which has an important role.
◀ To measure blood
pressure, a cuff
squeezes the patient’s
arm. Changes in blood
sounds indicate the
pressure.
Tube Pressure
Blood Pressure
Blood pressure is the force of moving
blood against the walls of blood vessels.
This force comes from the heart’s
pumping.
The circulatory system works best
under a certain range of blood pressures.
If the pressure drops too low, blood will
circulate poorly. If pressure rises too high,
it could cause a blood vessel to burst or
the heart to be damaged.
For otherwise healthy people, high
blood pressure is a more common
problem. As the body ages, arteries can
become narrower and stiffer. Smoking
tobacco and eating too many fatty
foods can also damage arteries. Blood
pressure rises as the heart is forced to
pump harder.
Quick Check
Critical Thinking How might fatty
foods contribute to high blood
pressure?
Model the heart and blood pressure by
blowing air through openings of
different sizes.
Materials cardboard tube, waxed
paper or aluminum foil,
rubber band, scissors
What to Do
Use Models Use a
cardboard tube
to model an
artery. Your
mouth and
lungs will model
Step
the heart. Hold the
tube at your mouth and blow air
through it. Record the results.
Compare Use the rubber band to
secure waxed paper or aluminum foil
across one end of the tube. Then cut a
hole about the size of a quarter. Repeat
step 1, and compare the results.
Compare Repeat step 1 again with a
new piece of paper and a hole the size
of a pin prick.
Draw Conclusions
Interpret Data How can narrow arteries
lead to heart disease?
31
EXPLAIN
Heartbeats
The heart works differently from other
muscles. Its different regions contract and
relax in a regular cycle. One complete cycle
is called a heartbeat. Typically the heart
beats from 60 to 100 times a minute.
Doctors can use this signal to study the
heart. By measuring and recording electrical
changes through the skin, doctors can learn
how well the heart is working. This
measurement is called an electrocardiogram
(i•lek•troh•KAHR•dee•uh•gram), or EKG.
An EKG is a kind of line graph. The
A nerve from the brain affects the rate,
spikes and dips of the line repeat in a cycle.
or speed, of heartbeats. But the heart would
This shows the cycle of the heart beating.
continue beating even if that nerve stopped
working. An electrical signal within the
Quick Check
heart controls how it beats.
Critical Thinking Why might an EKG be
more useful than listening to a heartbeat
with a stethoscope?
▼ To obtain an EKG, wire leads are
attached to the patient’s skin.
Doctors often want patients to
exercise during the procedure.
This shows how the heart responds
to stress.
32
EXPLAIN
Visual Summary
The circulatory and
respiratory systems
work together to
bring oxygen to body
cells and to remove
carbon dioxide.
Think, Talk, and Write
Main Idea By working together, what
job do the circulatory and respiratory
systems do?
Vocabulary Inside the lungs, gases
move between capillaries and ______.
Sequence Beginning with the right
Airways in the lungs
end in tiny air sacs
called alveoli. Gases
pass between alveoli
and capillaries.
atrium, describe the path that blood
takes through the body.
First
Next
Last
The heart, arteries,
veins, and capillaries
move blood through
many paths in the
body, but all paths
lead through the
heart and lungs.
Blood has many
parts, including red
blood cells, white
blood cells, and blood
serum. Blood
platelets and proteins
help form blood clots.
Writing Link
Critical Thinking If blood did not
form clots, what harm could be caused
by even a small cut on the skin?
Test Prep What part of a tree is most
like the trachea?
A trunk
B upper branches
C small twigs
D leaves
Test Prep What is the role of
hemoglobin?
A forming blood clots
B carrying glucose
C carrying oxygen and carbon dioxide
D fighting invaders
Art Link
Journal Writing
Healthy Heart and Lungs
Write journal entries from the
perspective of a red blood cell as it
travels through the circulatory system.
Use vocabulary words from the lesson.
Research ways to keep your heart and
lungs healthy. Present one or more of
these ways in a poster. Display posters
around the classroom or school.
33
EVALUATE
Heart Surgery Pioneers
If the heart ever stopped pumping blood,
Surgeons also can replace faulty heart
the body would quickly die. This is why
valves and other parts of the heart. When a
heart disease is very dangerous. A faulty
new heart or valves are transplanted, the
heart is difficult to fix or replace.
patient’s body does not recognize the new
tissue. It may “reject” the heart by
In 1967 Dr. Christian Barnard led the
attacking it as though it were a germ.
team that performed the first successful
heart transplant. The patient only lived for Anti-rejection drugs help the body
accept a new heart and heart tissues.
a few weeks, but greater successes soon
followed. The first permanent artificial
If a patient has blocked arteries, heart
heart was put into a patient in 1982.
surgeons can do bypass surgery. This lets
Today heart transplants are quite common. the blood flow around the blockage.
A surgical team worked for 9 hours to transplant a new
heart into their patient. Dr. Barnard is the tall man at the left
of the photograph. ▼
34
EXTEND
History of Science
▲ Using a stethoscope, a doctor can listen
to heartbeats. An irregular rhythm can
indicate potential health problems.
Write About It
Draw Conclusions
1. Why would a heart transplant take
many hours to perform?
2. Would it be better to replace a
patient’s entire heart or only a part of
the heart, such as a valve? Why?
▲ Doctors have also experimented
with artificial hearts, such as the
Jarvik-7 shown here.
35
EXTEND
Lesson 4
Digestive
System
The small intestine is full of folds. Stretched out,
it is about as long as a school bus! How do folds
help the small intestine take up nutrients?
36
ENGAGE
Materials
Why is the small intestine full of
folds?
Make a Prediction
One of the main jobs of the small intestine is to
absorb water and nutrients. If you use paper to model
the way the small intestine absorbs water, which type
will absorb the most water? Make a prediction.
• construction paper
Test Your Prediction
• ridged paper towels
Pour the same amount of water into each
graduated cylinder. Observe and record the water
levels of the graduated cylinders.
• plain paper towels
• printer paper
Fold the construction paper twice lengthwise.
• water
Dip the construction paper into a graduated
cylinder until half is covered in water.
• 4 graduated
cylinders
After 30 seconds remove the paper. Observe and
record the water level in the graduated cylinder.
• stopwatch
Repeat steps 2 through 4 for the other paper
types.
Step
Draw Conclusions
Which type of paper absorbed the most water?
Do these results support your prediction?
Compare How does the structure of the paper
that absorbed the most water compare to the
small intestine?
Infer What is the function of the small intestine?
Explore More
Step
What do you think would happen if you repeated the
experiment using a bath towel? Design and perform
an experiment. Then share your results.
37
EXPLORE
What does the digestive system do?
▶ Main Idea
The digestive system
breaks down food into
nutrients that the body
absorbs.
▶ Vocabulary
nutrients, p. 38
digestive system, p. 38
enzyme, p. 38
metabolism, p. 42
All body cells need energy to stay alive and to do
their jobs. This energy comes from food. Yet the food
you eat every day comes in very big pieces. Cells are
too small to use food as large as an apple or even one
bite of an apple.
Tiny food pieces that the body can use are called
nutrients. The body needs many kinds of nutrients, and
different foods are rich in different kinds. Eating a
variety of foods will help you get all of the necessary
nutrients.
Food also contains materials that cannot be digested.
Such material is called dietary fiber. Many grains, fruits,
and vegetables contain fiber. It is removed from the body
as solid waste. Even though it cannot be digested, dietary
fiber is an important and healthful part of the diet.
Water is also a part of many foods. Every body cell
needs water, as does the blood.
Digesting Food
The digestive system is the set of organs that
breaks down food into tiny pieces. The organs of the
digestive system form a tube through the body. Food is
broken down further and further as it moves along the
tube. When food pieces are small enough, they are
taken up into the blood.
Food is digested in two ways. In mechanical
digestion, food is torn or ground up into smaller parts.
The teeth begin mechanical digestion. In chemical
digestion, food is broken apart chemically. This happens
in the mouth, the stomach, and the small intestine.
The digestive system uses organs called glands to aid
in chemical digestion. These glands make products
called enzymes. An enzyme helps a chemical change
take place. Enzymes for digestion come from glands in
the mouth, the pancreas, and other organs.
▲ Both mechanical and
chemical digestion begin as
soon as you bite into a piece
of food.
38
EXPLAIN
Quick Check
Critical Thinking Is all food taken up into the blood?
Why or why not?
Nutrients from Food
Bread, rice, and pasta are rich in
starches, which are types of
carbohydrates. They are broken
down into glucose, the molecule
that cells use for energy.
Fruits and vegetables have
dietary fiber. They also contain
many vitamins and minerals. Cells
need these nutrients to carry out
life processes.
Meats and beans are rich in
proteins, which are used for cell
growth and repair.
Milk products have calcium, an
important mineral for healthy
bones and teeth.
Most foods are rich in some
nutrients and poor in others. A
healthful diet includes foods
from all of the food groups.
Oils are found in nuts, fish, and
other foods. They contain lipids, a
nutrient that includes fats and
other substances. Body cells need
a small amount of lipids.
Read a Photo
Why is it important to eat a variety
of different foods?
39
EXPLAIN
Digestion
When you put food into your mouth, it
begins a long journey through your
digestive tract. First, your teeth grind and
tear the food into smaller pieces. While this
happens, glands in your mouth release
saliva. Saliva is a mixture of water and
enzymes. It softens food and begins the
process of chemical digestion. Your tongue
and muscles in the back of your throat
help you swallow the mass of food, which
is called a bolus (BOH•lus).
This mass then moves down your
esophagus (ih•SAH•fuh•gus), a long, thin
tube that is lined with muscles. These
muscles squeeze the bolus down to the
next organ, the stomach.
The stomach is a muscular pouch inside
the belly. Here food is digested both
mechanically and chemically. The stomach
churns food back and forth, and it adds
acids and enzymes that help break down
proteins. The food is changed into a form
called chyme (kighm). Chyme is like a thick
soup.
The Digestive System
1
1
Mouth The mouth is where
digestion begins.
2
Esophagus The esophagus is a
tube that connects your mouth to
your stomach.
3
Liver The liver adds digestive
juices to food.
2
3
4 Stomach The stomach is a hollow
bag with muscular walls.
5
4
5
6
6 Gallbladder The gallbladder is a
pear-shaped organ that stores
digestive juices produced by the
liver.
7
Small Intestine The small intestine
connects the stomach and the
large intestine. It absorbs
nutrients.
8
Large Intestine The large intestine
eliminates undigested waste.
7
8
40
EXPLAIN
Pancreas The pancreas is an organ
that produces several important
enzymes.
Depending on the kind of food eaten,
the stomach may take several hours to
release the chyme. The chyme enters the
small intestine, a coiled tube where most
chemical digestion takes place. Though it
is called the small intestine, only the width
of this tube is small. Its length is about
7 meters (23 feet)!
Model the Small
Intestine
Materials: string, meterstick, scissors
Near the beginning of the small
intestine, enzymes from the pancreas and
gall bladder are added into the chyme.
Once these enzymes do their work,
nutrients are ready to be absorbed into the
blood. This happens in the many folds of
the small intestine called villi (VIH•ligh).
What to Do
Food that is not absorbed passes into a
wider, shorter tube called the large intestine.
From here, water is absorbed into the blood.
Most materials that remain will leave the
body as waste.
Draw Conclusions
Measure Wrap string around the
length of a meterstick to measure
7 meters. Cut the string and
stretch it out.
Carefully coil the string to a size
that could fit inside your
abdomen.
Infer What does this model show
about the way food moves
through the small intestine?
◀ Villi of the small intestine
soak up water and nutrients
into the blood. They work
much like tiny strands of
cloth on a towel.
Quick Check
Critical Thinking Why does the small
intestine need to be so long?
41
EXPLAIN
Metabolism
A huge number of chemical changes
take place as the body breaks apart food
and uses its energy. Together, these
chemical changes make up the metabolism
(muh•TA•buh•lih•zum) of the body.
Metabolism includes the breaking down of
food for its energy. It also includes the
building up of new body tissues.
Many factors affect metabolism. One
factor is diet. As you know, food provides
energy to the body. The energy in foods is
measured in Calories. If the body takes in
more Calories than it needs, it typically
stores the extra Calories as fat.
Exercise helps use up the energy from
food. It also builds up muscle mass. Muscle
cells, even when they are resting, use up
many more Calories than fat cells. Exercise
can increase a person’s overall metabolism
by increasing his or her muscle mass.
The body’s metabolism is always
changing. It speeds up when the body
exercises, and it slows during times of rest
and sleep. It also slows gradually as the
body ages.
Sometimes the body’s metabolism does
not work correctly. It releases too much or
too little of a certain hormone. Metabolic
disorders can often be treated with surgery
or by taking oral or injected hormones.
Quick Check
Critical Thinking Why is it important to
balance diet and exercise?
◀ A dietitian or nutritionist can
help people choose the diet
that’s right for them.
42
EXPLAIN
Visual Summary
Food provides the
nutrients that body
cells need. Many
nutrients are used for
energy. Others are
used for growth and
other life processes.
The digestive system
breaks down food
into nutrients. Both
mechanical and
chemical digestion
begin in the mouth.
Think, Talk, and Write
Main Idea What happens to food after
it is eaten?
Vocabulary Glands make ______ that
aid in chemical digestion.
Cause and Effect Why can
professional athletes eat more food
than most people eat, yet still not gain
weight?
Cause
Effect
Critical Thinking Compare actions of
Glands make
enzymes that aid
chemical digestion.
Villi are folds of the
small intestine that
absorb nutrients into
the blood.
Diet and exercise
affect metabolism,
which is the total set
of chemical changes
in the body.
Writing Link
the digestive system that are under a
person’s control with those that
happen automatically.
Test Prep Breads and pasta are
rich in
A carbohydrates.
B proteins.
C fats.
D vitamins.
Test Prep Food passes through all of
these organs EXCEPT the
small intestine.
esophagus.
stomach.
pancreas.
A
B
C
D
Math Link
Prepare for an Interview
Calculate Ratios
What if a company began advertising a
product called “The Perfect Food”?
Write questions to ask about this food.
Describe why these questions and their
answers are important.
Research an animal’s body length and
the length of its digestive tract. Then
find the ratio of these lengths. Compare
the ratios between plant-eaters, such as
sheep, and meat-eaters, such as lions.
43
EVALUATE
Lesson 5
Nervous System
Nerves connect the brain with organs throughout
the body. Just how fast can this system work?
44
ENGAGE
Materials
Can reaction time change?
Form a Hypothesis
Test your reaction time by trying to catch a falling
object. What variables might affect your reaction
time? Will you react faster to a sound or a sight?
Write your hypothesis in the form: “If my eyes are
shut, then my reaction will be….”
Test Your Hypothesis
• ruler
Create a chart like the one shown to record your
results.
Hold a ruler vertically with your hand at the top of
it. Have your partner put one hand near the
bottom of the ruler without touching it.
• paper
• pencil
Step
Drop the ruler, and observe the spot where your
partner caught the ruler. This is the control. The
closer your partner’s hand is to the bottom
number, the quicker the reaction. Repeat the test
five times, making sure to record the data from
each test.
Repeat the activity, but have your partner close
his or her eyes. Make a noise as you drop the ruler.
This is the variable. Repeat the test five times and
record your results.
Draw Conclusions
Interpret Data Compare the reaction times for
the control and the variable. Do you notice any
patterns? Was your hypothesis correct?
Step
Infer Why would reaction time vary according to
whether a person’s eyes are open?
Explore More
How will reaction time change if your partner uses the
other hand to catch the ruler? Repeat the experiment,
and compare your result to those of the other teams
in your class.
45
EXPLORE
How do nerves work?
▶ Main Idea
The nervous system
controls thoughts and
actions.
▶ Vocabulary
If you put your ear next to a telephone line, would
you hear people’s voices? Of course not. Telephone
lines carry electrical signals. At the end of a line, a
receiver translates those signals into sounds.
In some ways the nervous system acts like telephone
lines for the body. The nervous system uses nerves to
carry messages quickly. The message of a single nerve is
in the form of an electrical signal called an impulse.
nervous system, p. 46
neuron, p. 46
Neurons
spinal cord, p. 47
A nerve cell that carries impulses is called a neuron
(NOOR•ahn). Impulses travel through a neuron in one
direction only.
brain stem, p. 48
cerebellum, p. 48
cerebrum, p. 48
reflex, p. 51
The tiny, fingerlike parts of a neuron are called
dendrites. Dendrites carry impulses to the cell body,
which is the central part of the neuron. The cell body,
in turn, sends an impulse down the axon. The axon
carries the impulse to the end of the nerve.
Neuron Impulses
◀ Like a telephone
line, a neuron
carries messages in
the form of an
electrical signal.
axon
axon terminals
cell body
dendrites
46
EXPLAIN
The ends of two neighboring neurons
are very close but do not touch. The tiny
space between them is called a synapse
(SIH•naps). When an impulse reaches the
end of an axon, a chemical is released
across the synapse. This is how nerves
communicate.
The Nervous System
brain
A single impulse cannot be made
stronger or weaker, nor can it be made
faster or slower. However, a series of
impulses can be sent down an axon at
different rates. These rates determine the
effect of the neuron.
Parts of the Nervous System
The nervous system has three main
parts: the brain, the spinal cord, and
peripheral (puh•RIH•frul) nerves. The
spinal cord is a long column of nerves
that extends from the base of the brain
down the back. It acts to relay messages
between the brain and the rest of the body.
The brain and spinal cord together
make up the central nervous system. All
other nerves make up the peripheral
nervous system. The word peripheral
means “to the side.” Some peripheral
nerves are quite long. The longest nerves
span between the toes and the spinal cord.
The brain is involved in almost every
message that the nervous system carries.
These messages may travel to the brain,
from the brain, or entirely within it.
Quick Check
spinal cord
peripheral
nerves
▲ Most nerves that lead directly to or
from the brain are part of the spinal
cord. Peripheral nerves span across
the rest of the body.
Critical Thinking If nerves are like
telephone lines, which body part acts
like the telephone receiver?
47
EXPLAIN
The Brain
The adult brain is made of about
100 billion neurons. It is the body’s most
complex organ—and one of the most
important.
The three largest parts of the brain are
the brain stem, the cerebrum, and the
cerebellum. Each of these parts, in turn, is
divided into many smaller parts and
regions. Although the parts do separate
jobs, they all work together to control
nearly every action of the body.
The brain stem is the part closest to the
spinal cord. It controls breathing, heart
rate, the cycle of sleeping and waking, and
other actions that keep the body alive.
The cerebellum (ser•uh•BE•lum) helps
control balance and posture. It receives
messages from muscles and from the inner
ear, which has a sense organ for balance. It
uses all of this information to move
muscles in the right way to keep the body
from falling.
The cerebrum (suh•REE•brum) is the
largest part of the brain. It has the unique
power to think, decide, and act.
The Cerebrum: A Closer Look
The outer surface of the cerebrum looks
quite different from the layers beneath. The
outer surface, called the cerebral cortex, is
made of cell bodies of neurons that are
packed closely together. This tissue is also
known as gray matter.
When you remember, think, or create,
you are using your cerebral cortex. This is
the part of your brain that interprets
information from the senses, recognizes
language, and is the source of many
emotions.
Rather than having a smooth surface,
the cerebral cortex has many folds and
grooves. This increases its surface area.
Although other animals have larger skulls
and heads, none have as much gray matter
as humans do in proportion to the size of
their brains.
The Brain
The cerebrum is
responsible for
thoughts, feelings,
memories, and
conscious motion of
body parts. It has
many lobes, each
with its own
function.
The brain stem
controls
essential body
functions and
connects the
brain to the
spinal cord.
48
EXPLAIN
The cerebellum
keeps the body in
balance.
Beneath the gray matter is the white
matter. It is made of axons of neurons.
White matter carries messages between
the gray matter and the rest of the body.
In addition, certain regions help release
hormones, as well as feel hunger, thirst,
and other sensations.
The brain’s cerebrum is divided into
left and right halves called hemispheres
(HE•muh•sfihrs). According to many
scientists, the two hemispheres think in
different ways. The left hemisphere is
more logical, while the right hemisphere
is more creative.
Each hemisphere is divided into
separate sections called lobes. Each lobe
fills a specific role. One lobe is involved
in vision. Another lobe is involved in
speech, memory, and hearing.
▲ The cerebrum has gray matter on
the outside and white matter on
the inside. Gray matter allows
intelligent thought.
Quick Check
Critical Thinking How can the
brain do tasks without being aware
of them?
Although the cerebrum chooses how to
move the skeleton, the cerebellum
keeps it in balance. ▶
49
EXPLAIN
Peripheral Nerves
Peripheral nerves travel throughout the
body. Twelve pairs of them connect directly
to the brain. All others connect to the
spinal cord.
Like other nerves, peripheral nerves
carry messages in one direction only.
Nerves that carry messages to the brain are
called sensory nerves. These include nerves
for sight, hearing, smell, touch, and taste.
Other nerves carry information about the
position of the body or the saltiness of the
blood. Still others sense temperature, pain,
and vibration.
Anything that triggers a sensory nerve is
called a stimulus (plural: stimuli). A touch
to the skin, food on the tongue, and a
painful injury are all examples of stimuli.
Nerves that carry messages from the
brain are called motor nerves. These nerves
lead to muscles, including those that move
bones, the heart, and other organs. Motor
nerves and sensory nerves are connected by
associative nerves, or interneurons.
Sensory nerves send messages to the
brain all the time. The brain processes
these messages. In response it may send
messages down motor nerves. Often it does
so automatically, without awareness or
thought.
In many cases a message from the body
may trigger an emotion, a desire, or a
physical reaction. If the blood is too salty,
the brain senses thirst. If a spot in the skin
is dry or prickly, the brain senses an itch.
A Reflex Action
A tack pricks the
finger (stimulus).
Sensory neurons transmit an
impulse to associative neurons.
Associative
neurons
transmit
an impulse
to motor
neurons.
You pull your finger away
from the tack (response).
50
EXPLAIN
Motor neurons transmit an
impulse to the muscles.
Usually the brain is the only
connection between sensory and motor
nerves. The exception is a reflex. A reflex
is a muscle movement that happens very
quickly and automatically, without the
involvement of the brain. Doctors can test
some reflexes to make sure the nervous
system is working correctly. Tapping a
tendon in the knee with a small rubber
hammer causes the knee-jerk reflex—the
lower leg kicks outward.
Tricks of Sight
What to Do
Observe Look at the diagram below.
Compare the two yellow circles. Which
appears larger? Record your
observations.
Sense Organs
You see with your eyes, hear with your
ears, and smell with your nose. These
organs, however, do not work all by
themselves. Nerves connect each organ
directly to the brain. The brain interprets
the information it receives.
Each sense organ has nerves that
respond to a special type of stimulus. The
back of the eye, for example, has cells that
change when light strikes them. The
changes trigger signals in nerves that lead
to the brain. A lobe in the cerebrum uses
these signals to form a picture.
Measure Using a ruler, find the width of
each circle. Record your measurements.
How do the sizes of the yellow circles
compare?
Observe Stare at any of the blue
squares in the image below. Then look
at the small white dots in the grid. How
do they appear? Record your
observations.
The ear has tiny bones and other
tissues that move in response to sound. A
nerve connects the ear to the brain. The
cerebrum interprets the information from
this nerve as noise, music, words, or other
kinds of sounds.
The nose picks up tiny particles that
hang in the air. The brain interprets these
particles as an odor, or smell.
Draw Conclusions
Quick Check
Critical Thinking How are reflexes
Infer Do these pictures trick the eyes or
the brain? Explain your answer.
different from other actions of peripheral
nerves? Why are reflexes useful?
51
EXPLAIN
Nerve Injuries and Repair
Some nerves are easy for the body to fix
or replace. For example, when the skin is
cut or scraped, nerve endings may be
damaged or lost. They typically grow back
and work normally again.
In other cases, however, the body does
not repair injured or dead nerves. Tissues
in the brain and spinal cord are examples.
A burst blood vessel in the brain can cause
a stroke, an event that often kills brain
tissues. Patients who suffer strokes may
never regain lost brain function.
Injuries to the brain and spinal cord can
also be very serious. This is why helmets
are so important when biking, skiing, or
playing sports, such as football and hockey.
When bones of the spine are injured or
broken, they can press against or damage
the spinal cord. This can affect the body’s
ability to move. As a general rule, the
higher up the spine that an injury strikes,
the greater the region of the body it affects.
Quick Check
Critical Thinking How might a spinal
▼ Although some injuries to
cord injury affect the ability to walk?
the spinal cord may never
heal, exercises and training
can help patients recover.
▲ Helmets used in sports are
designed to protect the head
and brain from damage.
52
EXPLAIN
Visual Summary
Like telephone wires,
the nervous system
carries messages
across the body. A
neuron is a nerve cell
that carries a
message.
The cerebrum,
cerebellum, and
brain stem are three
parts of the brain.
The cerebral cortex
thinks, remembers,
and imagines.
Think, Talk, and Write
Main Idea What is the role of the
nervous system?
Vocabulary Balance and posture are
controlled by the ______.
Sequence A boy feels thirsty and then
drinks some water. Describe how his
nervous system worked. Include at
least four parts of the system.
First
Next
Last
Most peripheral
nerves travel from
the spinal cord to
body parts. Nearly all
carry messages to or
from the brain.
Sense organs respond
to light, sounds, and
other stimuli, and
then send information
through nerves to the
brain.
Writing Link
Critical Thinking Why is it useful that
the cerebral cortex stays unaware of
many functions of the brain?
Test Prep An action that involves
peripheral nerves only is a
muscle contraction.
muscle movement.
reflex.
response to an emotion.
A
B
C
D
Test Prep Where is the gray matter in
the brain?
A on the cerebrum
B on the cerebellum
C in the right hemisphere
D in the left hemisphere
Math Link
Book Report
Estimate Volume
Many science-fiction stories involve
creatures with very powerful brains or
senses. Find such a story from the
library. In your report, compare the
human brain to the brain in the story.
Propose a plan to estimate the volume
of your brain. Use a ruler or measuring
tape and the formula for the volume of
a sphere or a rectangular prism. Discuss
your plan with a partner, and then try it.
53
EVALUATE
Wide Nerves for Giant Squids
Invertebrates are animals without
backbones. Most invertebrates’ bodies do
not grow very long. But that is not the case
for squids. The giant squid is the world’s
largest invertebrate. The longest recorded
giant squid was 18 meters (59 feet) long.
In 2007, New Zealand fishermen caught
a colossal squid, which is not as long as a
giant squid, but much wider and often
much heavier—this one weighed 450 kilograms (990 pounds)!
▼ A giant squid uses its tentacles to capture
fish and other prey. Wide, fast-acting
nerves allow this.
54
EXTEND
Animal Bodies
Nerves wrapped in myelin help
vertebrates grow very tall or
very long.▼
How can a squid grow so big? One reason is that it has extremely thick axons, or
nerve fibers. Thick axons carry impulses
much faster than narrow nerves do. By
using nerves that communicate quickly, the
squid’s brain can control distant body
parts.
Many vertebrates also grow tall or long,
yet their nerves are not unusually thick. A
white substance called myelin (MY•uh•luhn)
speeds up the rate of nerve impulses.
Myelin is made of a layer of proteins
between two layers of lipids. It forms a
sheath, or coating, around axons. A myelin
sheath keeps the impulse contained in a
small area around the axon. This means
that the chemicals that transmit the
impulse from one nerve cell to another do
not have far to move.
Write About It
Summarize Using the Internet or other
resources, research additional information on
how different kinds of animals have different
nerves. Make a poster displaying your findings.
Include a graph or chart that shows animals’
sizes.
55
EXTEND
Lesson 6
Excretory System
The kidneys have millions of tiny bumps like
these. How does the structure of the kidneys help
them remove wastes from the body?
56
ENGAGE
Materials
How do your kidneys filter out
waste?
Purpose
Your kidneys filter waste out of your blood using a
special kind of membrane. The membrane has very
small openings that allow some molecules to pass
through but not others. Waste particles are kept
inside the kidneys and useful substances are
sent back into the body. Make a model of a
kidney’s membrane.
•
• cornstarch
• measuring spoon
Procedure
• water
Experiment Mix 1 teaspoon of cornstarch and
• eye dropper
200 mL of hot water in a beaker.
• 2 beakers
Mix 150 mL of water and 5 mL of iodine in the
other beaker.
• spoon
Pour 50 mL of the cornstarch water into the bag
and close it with a twist tie.
• iodine
Gently place the bag in the iodine solution without
letting the twisted top get wet.
• twist ties
• cellophane bag
Step
Observe Check the beaker every 3 minutes for 15
minutes. Write down your observations.
Draw Conclusions
What happened to the cornstarch in the bag?
Why do you think this happened?
How is the bag similar to the membrane of
the kidneys?
Explore More
Step
Would salt filter through the bag? What about
pepper? Why might one substance move through the
bag, but not another? How does this compare to the
kidneys’ function? Explain.
57
EXPLORE
How does the excretory system
work?
▶ Main Idea
Several systems eliminate
body wastes, including
solids, liquids, and gases.
▶ Vocabulary
excretory system, p. 58
urinary system, p. 58
liver, p. 58
kidney, p. 60
nephron, p. 60
Cells throughout the body produce wastes, or
materials the body cannot use. Removing these wastes
is the job of the excretory (EK•skruh•tor•ee) system.
Unlike other body systems, the excretory system
includes parts that work separately from each other.
These parts include the following:
• the urinary system, which filters the blood to
remove liquid wastes
• the end of the digestive system, which removes
solid wastes from food
• the respiratory system, which removes carbon
dioxide
• the integumentary system, or skin, which removes
water and salts through sweat
Wastes in the Blood
▼ Sweat glands in the skin are
part of the excretory system.
Many kinds of wastes collect in the blood. Carbon
dioxide is a waste gas that most cells produce. Other
wastes come from old cells or cell parts. Even medicines
can form wastes as they are broken down in the body.
Poisons may enter the body, too. A poison in the
blood is called a toxin. Toxins may come from the bite
or sting of snakes, bees, spiders, and other animals.
Toxins can also come from harmful bacteria.
The liver treats many of these wastes and toxins.
The liver is a large, reddish-brown organ in the middle
of the body, just below the diaphragm.
The liver does not remove wastes directly. It changes
them into products that can be removed more easily
later. One toxic waste is a compound called ammonia.
The liver changes it into urea (yoo•REE•uh), which is the
waste material in urine.
Quick Check
Critical Thinking Could the body survive without an
excretory system? Explain.
58
EXPLAIN
The Urinary System
Liver The
liver treats
wastes and
toxins in
the blood.
Kidneys These two organs
filter wastes from the blood
and produce urine.
Bladder The
bladder stores
urine until it can
be released.
Ureters Tubes
carry urine from
the kidneys to
the bladder.
Urethra This tube
carries urine
away from the
bladder and out
of the body.
59
EXPLAIN
All of your blood circulates through
your kidneys about 60 times a day. The
kidneys are a pair of bean-shaped organs
located near your back just above your
waist. They control the amount of
chemicals in the blood.
Urine collects near the center of the
kidney. From there it flows through tubes
called ureters (YOO•ruh•turz) to the bladder.
The bladder is a muscular bag that holds
urine. The brain tells the bladder when to
empty. Urine leaves the body through a
tube called the urethra (yoo•REE•thruh).
Inside each kidney are millions of tiny
filtering tubes called nephrons (NE•frahnz).
Nephrons get blood from capillaries and
separate waste from useful materials. They
send the waste into a larger collecting duct,
or tube. The waste is processed into urine.
Kidneys also control the amount of
water in the blood. If the blood is too
watery, the kidneys put the extra water
into the urine, making it lighter-colored. If
the blood is low on water, the kidneys will
make darker-colored urine with less water.
The Kidneys
The Kidney
artery
capillary
vein
nephron
renal artery
collecting duct
renal vein
ureter
Read a Diagram
Where do substances from the
nephrons go?
60
EXPLAIN
Health and the Urinary System
Kidneys often work well throughout a
person’s lifetime. The body can even live
with only one working kidney. However,
diseases of the kidneys and the urinary
system are common. Some can be serious.
Bacteria and other invaders sometimes
travel from the outer surface of the skin
into the lower part of the urinary system.
This is called a urinary tract infection.
These infections are especially common in
women. Women have shorter urethras than
men, so the bacteria do not need to travel
as far to reach the bladder. Many urinary
tract infections last only a short time and
cause only mild pain or discomfort.
However, an infection that reaches the
kidneys can cause serious damage.
Kidney stones are hard pieces of salts
and minerals that build up in the urinary
system. Large stones can block a ureter.
Passing them can be painful. Kidney stones
are more common among older adults than
other age groups.
Drinking lots of water and eating well
can help keep kidneys healthy. Wearing the
proper safety equipment when playing
sports is also important. Although a layer
of fat protects the kidneys, a hard blow to
the back or belly can injure them.
Quick Check
Critical Thinking Why do most
infections of the urinary system leave the
kidneys unharmed?
Comparison of a Full and an Empty Bladder
▲ With help from a special dye, X-ray pictures can show the urinary system. These
pictures show an empty bladder and a full bladder.
61
EXPLAIN
Dialysis and Transplants
Filtering with Water
Materials: paper towel, clear plastic cup,
water, food dye, sugar cube
What to Do
Color the sugar cube with food dye.
The colored cube models wastes in
the blood.
Cover the cup with a paper towel. Place
the colored cube on it.
Drip water over the cube. As the water
collects in the cup, observe the changes
to its color.
Draw Conclusions
Infer How does water help the kidneys
filter wastes?
A dialysis machine acts like an
artificial kidney. Dialysis has
saved many lives. ▼
Kidneys sometimes stop working
completely. This is called kidney failure.
One way to treat this problem is with
dialysis. Dialysis (digh•AH•luh•sus) is a
treatment that artificially filters the
blood to remove wastes.
In one common dialysis method,
blood is channeled through tubes that
carry it into a machine. The machine is
filled with a sugary liquid that draws
wastes out of the tubes.
Dialysis is only a temporary
solution. Treatments usually must be
repeated three times every week and
each treatment takes several hours.
Because dialysis cannot remove all
waste products, dialysis patients have
restricted diets.
A permanent way to treat a faulty
kidney is to transplant a new one. To
transplant is to move an organ from
one person’s body to another.
Doctors have had success with many
kidney transplants but not in all cases.
Even with the proper medicine, the
body sometimes rejects an organ that is
not its own. Transplants usually work
best when the replacement organ comes
from a close relative.
A person can live a normal life with
only one working kidney. For this
reason, people can choose to donate a
kidney to a patient with kidney failure.
Quick Check
Critical Thinking Why is dialysis
only a temporary solution to kidney
failure?
62
EXPLAIN
Visual Summary
The excretory system
removes wastes from
the body. Unlike
other body systems,
it includes parts that
work separately from
each other.
The kidneys filter
wastes from the
blood to make urine.
They are part of the
urinary system.
Think, Talk, and Write
Main Idea What is the job of the
excretory system?
Vocabulary The kidney is made of
millions of tiny filtering structures
called ______.
Sequence Explain how the liver,
kidneys, and bladder work in sequence
to remove wastes from the blood.
First
Next
Last
A nephron is a
structure in the
kidney that makes
urine. The kidneys use
millions of nephrons.
Diseases and injuries
can damage the
kidneys. Dialysis
filters blood
artificially, or a new
kidney can be
transplanted.
Writing Link
Test Practice The skin is part of the
excretory system because it makes
A carbon dioxide.
B sweat.
C vitamins.
D urea.
Test Practice Nephrons filter blood
from ______ in the kidneys.
A arteries
B veins
C capillaries
D alveoli
Art Link
Research Report
Kidney Poster
Research a disease that affects the liver
or the kidneys. Find out its cause,
effects, and treatment. Write a report to
show what you learned.
Make a poster that illustrates the
kidneys and how they work. Include
labels and captions.
63
EVALUATE
Lesson 7
Endocrine and
Reproductive
Systems
During a close race, an athlete may feel both
nervous and excited. How might emotions affect
how an athlete performs?
64
ENGAGE
How do emotions affect the
body?
Step
Make a Prediction
An emotion is a feeling, such as
happy, sad, excited, angry, or
frightened. How do emotions affect
the way the body works? Record
your prediction.
Emotion
Test Your Prediction
Excited
Make a chart like the one shown.
Record data Think of times
when you felt the emotions listed
in the chart. Complete the chart
by answering the question in
each column.
What other emotions have you
felt recently? Add a row to the
chart for each emotion, and then
repeat step 2.
What was I
doing when I
felt this
emotion?
I was running a
race.
Why did I feel
this way?
What was
happening in
my body?
I came from
behind to win!
My heart and
breathing rates
were fast, and
my leg muscles
were working
hard.
Bored
Frightened
Draw Conclusions
Analyze data Review your
answers. When do the heart, the
lungs, and the muscles work the
hardest? When do they work
more slowly?
Infer How do body systems
Relaxed
Angry
respond to emotions? Cite
evidence to support your answer.
Explore More
How could your emotions help you perform better in
a race or a game? Make a prediction, and design a
way to test it.
65
EXPLORE
What does the endocrine
system do?
▶ Main Idea
Hormones of the
endocrine system change
how body parts function.
The changes may be
temporary or permanent.
▶ Vocabulary
endocrine system, p. 66
hormone, p. 66
adrenaline, p. 68
insulin, p. 68
reproductive
system, p. 70
The organs of most body systems are joined closely
together. The glands of the endocrine (EN•duh•krin)
system, however, are scattered throughout the body.
The endocrine system works to send messages
through the blood to organs of other systems. Its
glands, or groups of special cells, make chemicals
called hormones to carry these messages. Many body
systems depend on hormones to work properly.
The nervous system also sends messages. But
hormones work differently. They travel more slowly,
and their effects usually last much longer.
Blood carries hormones from the endocrine glands
throughout the body. Yet each type of hormone
changes only certain kinds of cells, and it changes
them only in certain ways. In some cases a hormone
triggers cells to begin working or reproducing. In other
cases it signals cells to stop working or reproducing.
The effects of a hormone may last a few hours, a
few years, or a lifetime. Hormones help muscles to use
food, bones to grow longer, and mothers to carry and
give birth to babies.
If there is a problem with an endocrine gland, it
may make too much or too little of a hormone. Both
situations can be harmful to the body. Sometimes a
doctor can restrict the production of a hormone if a
person’s body is producing too much of it. He or she
can also give extra hormones if a person’s body is not
making enough.
◀ Human growth hormone makes
bones grow longer. In some
people the result is greater than
in others.
Quick Check
Critical Thinking How is the endocrine system
similar to other body systems? How is it different?
66
EXPLAIN
The Endocrine System
Hypothalamus This gland lies deep in
the brain. Its hormones control the
pituitary gland.
Adrenal glands These glands are near
the kidneys. They make adrenaline to
give cells extra energy.
Pituitary gland Some of its many
hormones affect growth, blood
pressure, childbirth, and the function
of other glands.
Pancreas It makes two hormones that
control the amount of glucose in the
blood.
Parathyroid glands They produce a
hormone that moves calcium from
bones into the blood.
Ovaries These organs in women make
hormones that cause the body to
develop female body traits.
Thyroid gland Its hormones help cells
use energy.
Testes These organs in men make
hormones that cause the body to
develop male body traits.
Read a Diagram
Which glands control the body’s
energy use?
67
EXPLAIN
Many Hormones
The endocrine system includes many
glands that make a huge number of
hormones. The glands respond to changes
in the blood or to messages from the
nervous system.
Adrenal glands
Have you ever noticed that your heart
beats faster when you feel frightened? The
adrenal (uh•DREE•nool) glands are the
cause. They make a hormone called
adrenaline (a•DREN•uh•lin), which is also
called epinephrine (eh•puh•NEH•frun).
Adrenaline makes the heart and lungs
work faster. It also alters the amount of
blood flow to some body parts and it
releases glucose into the blood. Together
these actions help the body use muscles to
move quickly.
Adrenaline is often nicknamed the “fight
or flight” hormone.
Adrenaline affects the body
in the same way whether a
threat is real or not.
▲ Insulin shots help people with diabetes
lead normal lives.
Pancreas
After a meal the pancreas (PAN•kree•us)
releases insulin (IN•suh•lun). Insulin is a
hormone that allows glucose to move from
the blood into cells.
Along with other hormones, insulin
controls the amount of glucose in the
blood. Too much glucose in the blood can
damage the eyes, the kidneys, and other
organs. If the level of glucose in the blood
gets too high, the pancreas releases more
insulin. Too little glucose starves cells of
the energy they need. If the blood’s glucose
level gets too low, the pancreas releases
less insulin.
When a person has a disease called
diabetes (digh•uh•BEE•teez), the body either
does not make or cannot use insulin
properly. Type 1 diabetes is caused by a
lack of insulin. This kind of diabetes often
occurs in childhood. In type 2 diabetes, the
body’s tissues do not respond to insulin.
This kind of diabetes usually happens to
adults. People with type 1 diabetes often
need to take insulin injections. A person
with severe diabetes can also have a
pancreas transplant.
68
EXPLAIN
Thyroid
A gland called the thyroid (THIGH•royd)
is located in the neck. It releases several
hormones that help the body use energy.
To make these hormones, the thyroid
needs a chemical element called iodine
(IGH•oh•dine). Iodine is a natural part of
many foods. It is also added to salt.
A faulty thyroid may produce either too
many or too few of its hormones. Too
many of them may cause weight loss and
nervous, jittery feelings. Too few may cause
weight gain and exhaustion.
Pituitary Gland
Some endocrine glands make only one
or two kinds of hormones. The pituitary
(puh•TEW•uh•tayr•ee) gland, however,
makes at least nine different hormones. For
this reason, it is often called the master
gland.
Model Insulin
Materials: pitcher of water; food dyes
colored yellow, blue, and green
What to Do
Make a Model Work in a small
group. Add a few drops of
green dye to the water. This
color models healthy blood.
Use Variables Use blue dye to model
glucose and yellow dye to model
insulin. Stir in a few drops first of blue
dye, then of yellow dye, then of blue
dye again. Observe the results.
As a group, decide how to restore
the green color that models healthy
blood. Carry out your plan.
Draw Conclusions
Infer How does this activity model
the role of insulin in the blood?
Pituitary hormones affect bones,
kidneys, and organs of the reproductive
system. Some affect other glands, including
the thyroid and the adrenal glands.
Quick Check
Critical Thinking Why does the body
need many kinds of hormones, rather
than just one or two?
This mass in
the neck is
called a goiter.
Lack of iodine
caused the
thyroid to
grow larger. ▶
pituitary gland
◀ This gland
is about the
size of a
pea, yet it
makes
many
different
hormones.
69
EXPLAIN
The Reproductive System
To reproduce is to make more
individuals of the same species. The job
of the reproductive system is to allow
people to have children.
All organs of the reproductive system
are present throughout life, even at birth.
They do not begin to fully develop until
the end of childhood.
The male and female reproductive
organs are quite different. Testes
(TES•teez) are organs in men that make
sperm cells. Ovaries (OH•vuh•reez) are
organs in women that make egg cells. A
sperm and an egg unite to form the first
cell of a new child.
Ovaries and testes also act as
endocrine glands. The hormones they
produce help develop the reproductive
system and the body traits of an adult
woman or man.
A woman who is carrying a
developing baby is described as pregnant.
Like nearly all female mammals, a
pregnant woman carries the developing
baby inside her body. The baby develops
inside the woman’s uterus (YEW•tuh•rus),
an organ just above the pelvis. The uterus
expands to many times its normal size as
the baby grows and develops.
▲ The first cell of this baby
came from the union of two
cells: a sperm cell from the
father and an egg cell from
the mother.
A typical pregnancy lasts for about 9
months. Then the baby is born.
Quick Check
Critical Thinking How does the
reproductive system differ from most
body systems?
70
EXPLAIN
Visual Summary
Glands of the
endocrine system
make hormones.
Hormones travel
through the blood to
change how organs
work.
Think, Talk, and Write
Main Idea What is the role of the
endocrine system in the body?
Vocabulary A hormone called ______
helps move glucose from the blood
into body cells.
Sequence Choose a hormone and
describe its path through the body.
Endocrine glands are
scattered across the
body. Some are as
small as a pea. Others
are much larger.
First
Next
Last
Adrenaline is the
“fight or flight”
hormone. Insulin
helps move glucose
into the blood.
The reproductive
system allows adults
to have children. Its
organs are different
in men and women.
Writing Link
Critical Thinking Does the size of an
endocrine gland relate to its
importance? Include an example.
Test Practice Which of these glands
is located in the neck?
A thyroid
B adrenal gland
C pancreas
D pituitary gland
Test Practice The job of the uterus
is to
A make egg cells.
B make sperm cells.
C carry a developing baby.
D make growth hormone.
Social Studies Link
Research Report
Goiters
Research a disease of the endocrine
system, such as diabetes, thyroid
disease, or Addison’s disease. Find out
about the causes, effects, and treatment
for each disease.
An enlarged thyroid is called a goiter.
Goiters are common in environments
where iodine is rare. Find out where
these places are and how goiters can be
prevented there.
71
EVALUATE
Lesson 8
The Human
Life Cycle
As the human body ages, it changes in
predictable ways. About how old are the people
in this photograph? How can you tell?
72
ENGAGE
Materials
How do boys and girls
grow differently?
Make a Prediction
Children and early teens grow taller every year. Do
you think boys and girls of your age grow differently
from one another? Make a prediction.
Test Your Prediction
• meterstick or
measuring tape
Measure Work in pairs. Remove your shoes, keep
• calculator
your feet flat on the floor, and have your partner
measure your height. Switch roles to measure the
height of your partner.
Record Data The teacher will draw a chart on
Step
the board with two columns—one for boys and
one for girls. Record your height in the
appropriate column.
Use Numbers Calculate the average height of
boys in the class. First add their heights together,
then divide by the number of boys.
Repeat step 3 for the girls in the class.
Draw Conclusions
Interpret Data Who is taller in your class, the
boys or the girls? How much taller are they?
Predict How do you think the height difference
will change during the next few years? Explain
your prediction.
Explore More
Why do some people grow taller than others? Do diet,
ethnicity, and genetics make a difference? Research
human growth and present your results to the class.
73
EXPLORE
How does the body change
over time?
▶ Main Idea
As the body ages, it
grows and develops
through the stages of the
human life cycle.
▶ Vocabulary
life cycle, p. 74
adolescence, p. 77
puberty, p. 77
A newborn baby girl is small enough for her parents
to hold in their arms. Over time she will grow into an
older child, then a teenager. When she is an adult, she
may choose to have a baby of her own.
Changes like these happen in a predictable pattern
that all human beings follow. This pattern is called the
human life cycle. A cycle is a series of events that
happen over and over. Although an individual human’s
life has a beginning and an end, reproduction ensures
that new lives continue the cycle. The human life cycle
includes many stages that occur at characteristic times
of life.
Before Birth
fetus at 20–24 weeks
of development
A human body is made of a huge number of cells.
Yet those cells all come from a single cell. This special
type of cell, called a zygote, forms when a sperm cell
and an egg cell unite. The cell divides into two cells,
which divide into four cells, then eight cells, and so on.
Inside the body of the mother, cells begin dividing in
a tube that leads from an ovary. Then the cells attach to
the wall of the uterus. During this time, the group of
cells is called an embryo (EM•bree•oh).
The uterus and embryo are connected by a structure
called the placenta (plu•SEN•tuh). The placenta brings
food and oxygen from the mother to the developing
baby.
As the embryo grows, early versions of body tissues
and organs are formed. After 8 weeks, the embryo
starts to resemble a baby, even though it is only about
1 inch long! At this stage, the embryo has become a
fetus (FEE•tus).
▲ A fetus gradually develops
organs and body systems
needed for life outside
the uterus.
74
EXPLAIN
Over many months, body parts develop that will
eventually allow the fetus to survive outside the
mother’s body. The fetus grows a skeleton and muscles,
as well as about 100,000 brain cells every minute.
Infancy
A baby is born after about 9 months of
development in the uterus. At birth, a
newborn uses his or her lungs and a few
other organs for the first time.
Young babies are called infants. Infants
need their parents or other adults to care
for them. They cannot eat solid food.
Instead they rely on their mothers’ milk or
formula for nutrition. When their needs are
not met, they will cry loudly for help.
Infants grow and develop rapidly. The
brain continues to develop, as do bones
and muscles. By 1 year old, most babies
will have tripled in weight, grown some
teeth, and be able to eat some solid food.
Many babies will have learned a few words
and are able to recognize other people.
Quick Check
Critical Thinking A fetus has developing
▲ The umbilical cord connects the fetus
lungs. Why are they not used until birth?
to the placenta. When it falls off, it
leaves a scar called the navel, or belly
button.
◀ More growth and
development takes
place in the first
year than in any
other.
75
EXPLAIN
Childhood
Growing Up
What to Do
Classify Which stage of life are you in
now? Explain how you know.
Make a timeline of important events
in your life. Begin with the day you
were born. Include other events that
you were told took place or that you
remember.
Draw Conclusions
Predict Add to your timeline by
predicting future events.
Childhood lasts from the end of infancy
to about age 12 or 13. With every year,
children learn new knowledge and skills.
They also take on new responsibilities in
their lives. However, children still rely on
adults to provide food, shelter, and
protection.
Very young children are called toddlers.
To toddle is to walk with short, wobbly
steps. Toddlers are still developing the
muscle control and balance that they need
to walk and run properly.
Children learn a great deal from
interacting with the world around them.
Young children begin to understand the
language that they hear every day. They
also learn to use words to express their
thoughts and needs rather than by crying
as infants do. Young children start to learn
cause and effect by experimenting. They
drop toys or other objects to watch them
fall. Simple games of peekaboo teach them
that just because they cannot see an object
does not mean it is gone forever.
Older children are more agile than
young children. They lose their baby teeth
and start to grow permanent teeth. Older
children are able to do many things that
adults do. They develop their muscles by
playing games and sports. They develop
their minds by reading books and studying
in school. They also develop their emotions
by building relationships with friends and
family members.
◀ By age 5, the muscular and
nervous systems are well
developed. Children can walk,
run, climb, dance, and learn new
ways to move their bodies.
76
EXPLAIN
Adolescence
After childhood, children enter
adolescence (a•dul•ES•unts). During
adolescence, the body grows taller and
begins to develop the traits of an adult.
The time that adolescence begins is
called puberty (PYEW•bur•tee). Many girls
enter puberty at around age 12 or 13,
although it can start at an earlier or later
age. Boys typically enter puberty about 2
years after girls do.
Adolescence is triggered by changes in
hormones from the endocrine system. In
girls, the ovaries release a hormone called
estrogen (ES•truh•jun). Estrogen causes the
breasts and female reproductive organs to
develop. It also helps begin a process of the
female reproductive system called the
menstrual (MEN•stroo•ul) cycle.
In boys, the testes release a hormone
called testosterone (tes•TAHS•tuh•rohn).
This hormone deepens the voice and causes
male reproductive organs to develop.
Other body changes involve the skin.
During adolescence, the skin makes more
sweat and may have acne, or pimples. Hair
also begins growing under the arms, in the
pubic area, and on boys’ faces.
Adolescents often sleep longer than
they did as children. Their bodies are
growing and changing very quickly,
which can be tiring.
Quick Check
Critical Thinking How are children
different from adolescents? How are
they alike?
Entering Puberty
age 7
age 12
Girls and boys enter puberty at
different ages. Adolescence
brings many changes to the body
and the mind.
age 17
Read a Photo
How do the boys’ and girls’ heights
compare in each of these photos?
77
EXPLAIN
▲ Humans of all ages can learn from each other and
from their own experiences.
Adulthood
When adolescence ends, the body has
stopped growing taller and all body
systems have developed fully. The body is
described as mature, or fully grown.
Adulthood is the mature stage of the
human life cycle.
Adults may choose to have children.
By having children, they are continuing the
human life cycle. Their children will grow
and develop, just as they did.
A woman may continue to give birth to
children as long as her menstrual cycle
continues. The menstrual cycle stops at a
time called menopause (MEN•uh•pawz).
Women often reach menopause in their 40s
or early 50s.
The body of an adult may appear to
change very little from year to year. Yet
cells always change as they age. Gradually
cells lose their ability to divide and
reproduce. While important body systems
continue working, many slow down.
By age 60 or 70, the body shows many
signs of a long life. Wrinkles may line the
skin, and hair may turn gray. Years of use,
illnesses, and diseases may weaken many
body parts. Many people live into their 80s
or 90s.
Death is the end of life. It occurs when
body systems stop working permanently.
Quick Check
Critical Thinking How does the adult
body change as it ages?
78
EXPLAIN
Visual Summary
Humans grow and
develop in stages of
the human life cycle.
Birth occurs after
nine months of
development inside
the mother’s body.
Childhood is a stage
of rapid growth of
both the body and
the mind. Older
children can do many
things that adults can
do.
During adolescence,
the body grows taller
and takes on the
traits of the adult.
Reproductive organs
develop in both boys
and girls.
In adults the body
gradually slows down
as it ages. By age 60
or 70, the body
shows many signs of
a long life.
Writing Link
Think, Talk, and Write
Main Idea List the stages of the
human life cycle.
Vocabulary Adolescence begins at a
time called ______.
Cause and Effect Why might older
adults suffer from more illnesses and
diseases than younger people?
Cause
Effect
Critical Thinking Does everyone pass
through the stages of the human life
cycle in the same way? Explain.
Test Prep A developing baby is
attached to the uterus by the
placenta.
fetus.
embryo.
adolescent.
A
B
C
D
Test Prep Adolescence is caused by
changes in the
muscular system.
skeletal system.
endocrine system.
immune system.
A
B
C
D
Art Link
Write a Magazine Article
Make a Collage
How do children, adolescents, and
adults compare? Write a magazine
article that answers this question.
Include your classmates’ ideas as well
as facts about stages of the life cycle.
Look in magazines, newspapers, or
online for photographs of people in
different stages of life. Make a collage
to show these stages, and include labels
and captions.
79
EVALUATE
At the
Hospital
At a large hospital, hundreds of patients
are treated every day. Some patients are
seriously ill. Others only need some
special attention.
Many people give birth in hospitals.
Specially trained doctors and nurses help
with the birth and can check the health of
the baby and the mother.
People with serious injuries or illnesses
go to the emergency room. Heart attacks,
broken bones, and severe asthma are just a
few of the conditions that emergency room
doctors treat on a daily basis.
▼ In the hospital, newborn
babies stay either in a
nursery or in rooms with
their mothers.
80
EXTEND
the nursery
▲ Some hospitals treat only
children. Others care for
children and adults in
separate sections.
Science, Technology, and Society
◀ Anyone who needs help right
emergency room
away is brought to the
emergency room. Doctors
save many lives here.
Hospitals have physical therapy
facilities. Special exercises help
patients recover from injuries,
diseases, or other events that
weaken bones and muscles. ▼
Sometimes patients need help getting strong
again after an illness or an injury. Hospitals
often have physical therapy facilities where
trainers work with people to build up their
strength, balance, and flexibility.
Some hospitals only treat certain types of
patients. Hospitals that only treat children are
called pediatric hospitals. There are also
hospitals that specialize in treating certain
organs, such as the heart. Others treat certain
diseases, such as cancer.
Write About It
Research What else can you learn about
hospitals? Do any have departments
that specialize in all of the different body
systems? Research using an encyclopedia
or other reference materials, and write a
short summary.
81
EXTEND
Lesson 9
The Body’s
Defenses
When germs invade the body, white blood cells
work to stop them. How can germs spread from
one person to the next?
82
ENGAGE
How quickly can germs spread?
Materials
Make a Prediction
Read steps 1 through 4. How many students will get
the germ? Make a prediction.
Test Your Prediction
Your teacher will give each student a pair of index
cards. Two students will receive cards marked
with an X. An X represents a germ. All other cards
are marked with a circle.
• 2 index cards per
student
Make a Model Walk around the room. When
• pencils or markers
your teacher says “stop,” find the student nearest
you. Exchange one card with this student.
Observe your new card. If it has an X
anywhere on it, add an X to both of your
cards. Otherwise add a circle to both.
Step
Repeat steps 2 and 3. Complete five
rounds.
After the fifth round, count the number of
students who have the germ.
Draw Conclusions
Use Numbers How accurate was your
prediction? If more rounds were added,
would all students receive the germ
eventually? Explain.
Infer What did the activity model about
the way germs spread?
Explore More
What if four students acted to stop the spread
of germs? If they stop trading cards once they receive
an X card, predict how the results will change.
83
EXPLORE
What causes disease?
▶ Main Idea
Diseases can harm the
body. They are fought by
the body’s defenses,
along with medicine and
medical technology.
▶ Vocabulary
A disease is an illness or a condition in which the
body does not work properly. Any organ or body
system can have a disease. Many diseases can attack at
any stage of the life cycle.
A symptom is a sign that the body has a disease. A
runny nose, a fever, or an upset stomach are common
symptoms of many diseases.
Infectious Diseases
infectious disease, p. 84
immune system, p. 86
white blood cell, p. 86
antibody, p. 87
antibiotic, p. 88
deer tick
Harmful germs are called pathogens (PA•thuh•jenz).
They can be bacteria, fungi, viruses, or parasites, such
as protists. Pathogens that invade a person’s body can
cause infectious diseases (in•FEK•shus di•ZEE•zuz). The
word infect means “to invade.” Infectious diseases that
can spread from person to person are also called
communicable (kuh•MYEW•ni•kuh•bool) diseases.
Animals can spread pathogens both to one another
and to humans. A disease called rabies, for example, is
transmitted by the bite of an infected animal. People
can get malaria and West Nile virus from the bites of
infected mosquitoes. Deer ticks can carry the bacteria
that cause Lyme disease.
Pathogens may spread through air, water, and food,
as well as from person to person. Many germs can be
spread by a sneeze or a cough. Covering your mouth
when sneezing or coughing helps to stop germs from
spreading. So does washing your hands after touching a
doorknob or other object that many people touch.
Infectious Diseases
Pathogens
Diseases
Bacteria
strep throat, tetanus, tuberculosis, plague, Lyme disease, whooping cough, typhoid fever
Fungi
ringworm, athlete’s foot, toenail fungus, valley fever, Darling’s disease (histoplasmosis)
Viruses
flu, chicken pox, cold, polio, rabies, measles, smallpox, AIDS, yellow fever, warts
Protists
malaria, African sleeping sickness, dysentery, giardiasis, black fever, Chagas’ disease
84
EXPLAIN
▲ The use of tobacco products
can cause many diseases.
Warnings on their labels are
required by law.
Many Diseases, Many Causes
Not all diseases are infectious. Some
diseases pass from parents to children
through genes. Cystic fibrosis is one
example. When a person has cystic fibrosis,
his or her body makes a substance called
mucus that is unusually thick and sticky.
The mucus causes problems in the lungs
and the digestive system.
Other diseases strike when body parts
wear down after years of use. For
example, the ends of bones are lined with
cartilage. As this cartilage wears away,
joints begin to hurt. This disease is called
arthritis. Many older people have problems
with arthritis in their knees, fingers, and
other joints.
Some diseases happen suddenly. If blood
stops flowing to a person’s brain, it results
in a stroke. A stroke may be caused by a
clot that clogs a blood vessel, blocking the
flow of blood. It can also happen when a
blood vessel breaks and leaks into the
brain. A stroke keeps oxygen and nutrients
from getting to brain cells, causing them to
die within a few minutes.
▲ Cholesterol is a material in
fatty foods. It can build up
inside arteries and cause
heart disease.
Poor health habits can lead to many
diseases. A diet with too many fatty foods,
for example, can make arteries stiff and
narrow. This makes the heart work harder.
The heart may fail suddenly in an event
known as a heart attack. Smoking can
cause diseases of the heart and lungs. Both
smoking and chewing tobacco increase the
risk for developing cancer.
Cancer is a dangerous disease that has
many different causes. It can strike any
organ. Most types of cancer are not
infectious. Cancer starts when a group of
cells divide incorrectly and rapidly. The
cells may form a mass called a tumor.
Cancer cells and tumors can spread across
the body, sometimes traveling to distant
body parts. Scientists continue to study the
different causes of cancer in hopes of
preventing it. Many types of cancer can
now be treated, and a few can be cured.
Quick Check
Critical Thinking Why is it that some
diseases are infectious while others are
not?
85
EXPLAIN
Fighting Disease
Fortunately, the body has ways to
prevent diseases. It can also fight off many
diseases when they attack.
The Immune System
To fight pathogens, the body uses the
immune system. The immune system is
made up of different components. If one
component fails, the next one takes over.
The body’s first line of defense is the
integumentary system. The skin acts like a
wall to stop germs from invading. Tears
wash germs out of the eyes. Nose hair,
mucus, and earwax trap germs. Saliva and
stomach acid can kill germs, too.
Despite these defenses, germs often find
paths into the body. A wound in the skin is
one such path. If germs get into the body,
another portion of the immune system
takes action.
Have you ever gotten very hot when
you were sick? A fever is a rise in body
temperature that also helps to fight
invaders. It slows the growth of some
pathogens and helps infection-fighting cells
do their jobs.
Some cells in the blood have the job of
fighting off germs that attack the body.
They form a group of cells called
white blood cells. Some types of white
blood cells are best at killing bacteria.
Others are best at killing viruses.
white blood cell
◀ Certain kinds of white
blood cells begin
working to defend the
body as soon as germs
invade.
86
EXPLAIN
Two special types of white blood cells
are called T cells and B cells. These cells
travel throughout the body, fighting
invaders wherever they meet them.
Vaccines
T and B cells work together to make
antibodies. Antibodies are proteins that
can attach to pathogens. The pathogens are
then broken apart, either by other proteins
or by other white blood cells. Specific
antibodies are made in response to specific
pathogens.
The immune system keeps a few copies
of every antibody it has ever made. There
are also certain T cells that “remember”
specific pathogens. This means that if the
same pathogen attacks the body again,
B cells would quickly make copies of the
proper antibodies. This explains why people
get some diseases, such as chicken pox, only
once in their lives.
Doctors use vaccines to prepare the
immune system for fighting serious
diseases. A vaccine is made of a pathogen
that is dead or weakened so that it cannot
damage the body. When white blood cells
meet the pathogen in the vaccine, they
make antibodies against it. This makes
them ready to fight the real pathogen if it
should get into the body.
Vaccines have helped stop deadly
diseases that were once quite common,
such as smallpox and polio. Scientists are
working to develop new vaccines, too.
Quick Check
Critical Thinking Why can some
pathogens infect the body only once?
5 White blood
cells break
up the
pathogen.
Immune System at Work
2 T cell is
copied.
1 T cell
identifies
pathogen.
3 Some T cells attack
infected cells. Other
T cells tell B cells to
make antibodies.
4 Antibodies
attach to
pathogens.
87
EXPLAIN
Treating Disease
The body can fight many diseases on its
own. It can rid itself of a cold or the flu,
for example, in a few days. However, the
body needs help to fight more serious
diseases.
A medicine or drug is a substance that
changes how the body works. Vaccines are
medicines that prevent disease. Cough
syrup and aspirin treat the symptoms of
disease, such as cough and fever. Other
medicines help the body fight the cause of
a disease.
▲ All medicines must be used
properly. You should only take
medicines under adult supervision.
Some medicines must be taken only
under a doctor’s supervision. These are
called prescription medicines. The doctor
prescribes, or orders the use of, a particular
medicine. He or she tells the patient very
carefully how the medicine is to be used
and the results to expect.
Some medicines may be used without
an order from a doctor. These are called
over-the-counter medicines. Any adult may
purchase this kind of medicine.
An antibiotic is a medicine that kills
bacteria. The first antibiotic was penicillin
(pen•uh•SIL•un). It was discovered in 1928,
and over time it has saved many lives.
Many other antibiotics are now widely
used. All antibiotics are prescription
medicines.
Antibiotics do not kill viruses, however.
Illnesses caused by viruses, such as the
common cold, cannot be treated with
antibiotics.
◀ Pharmacists are medicine experts.
They fill prescriptions and help
people use them.
88
EXPLAIN
Other Treatments
Some diseases cannot be treated with
medicine alone. In many cases the body
may need surgery (SUR•juh•ree). A surgery
is also called a surgical operation. It is
usually performed by a doctor called a
surgeon.
In surgery, a surgeon uses special tools
to open the body and treat the disease. A
surgery may involve removing, replacing,
or repairing damaged tissues or organs.
Surgery must be performed under
sterile conditions. To be sterile (STAYR•ul)
is to be free of germs of all kinds. Sterile
conditions keeps germs from infecting the
patient’s body during surgery.
Read the Label
What to Do
Read the label shown below. Discuss
the information on it.
Analyze Data What is the name of the
medicine? How often should the patient
take it, and for what reasons?
Draw Conclusions
Infer Why do you think this medicine
must be prescribed by a doctor?
Town Drug Patient: Smith, Mary
Treating cancer may require a
combination of medicine, surgery, and
radiation. In radiation, a beam of energy
is used to kill cancer cells.
Quick Check
Critical Thinking What diseases could
not be treated with antibiotics?
123 Elm Street
Empire, NV 89405
(775)555-0123
Prescriber: Berman, J.S.
TAKE 1 TABLET UP TO 2 TIMES A DAY
AS NEEDED FOR DIZZINESS.
Meclizine, 12.5 mg tablets
Date filled: 08-24-2008
Quantity: 30 tablets
2 refills allowed
◀ By keeping conditions sterile, a
surgeon can open the body
without causing an infection.
89
EXPLAIN
▲ Penicillin, the first antibiotic, was
widely used for many years. Yet it
gradually lost its effectiveness
against many diseases.
Antibiotic Resistance
Unfortunately antibiotics become less
effective over years of use. Penicillin, for
example, once killed all kinds of bacteria.
Today it affects very few of them. Doctors
no longer use penicillin in its original form.
What caused this change? When
penicillin was discovered, only a few
bacteria could survive its effects. Those few
bacteria are said to be resistant to
penicillin. The resistant bacteria survived
and made copies of themselves. Over time
they became more common.
Resistant bacteria will grow in number
in response to almost any antibiotic. For
this reason doctors use the newest
antibiotics only when older ones no longer
work. They want the new medicines to last
as long as possible.
90
EXPLAIN
▲ Some strains of bacteria are
sensitive to antibiotics, and others
are resistant. The diameters of the
clear rings show how effective the
samples of antibiotics were.
When a doctor prescribes antibiotics,
they should be taken exactly as ordered.
This includes taking all of the medicine,
not skipping doses, and not sharing the
medicine with others. Even though you
might start feeling better after one dose of
antibiotics, you should take all of the
medicine prescribed. The first dose or two
of antibiotics may kill some bacteria, but
not all of them. Resistant bacteria might
require many more doses of antibiotics.
Some antibiotics must be taken for several
days, weeks, or even months, depending on
the type of illness. This helps to ensure that
all of the bacteria are killed.
Quick Check
Critical Thinking Why shouldn’t people
take antibiotics without a doctor’s order,
even if they feel sick?
Visual Summary
Diseases have many
causes. Diseases that
are caused by
pathogens are
infectious diseases.
Think, Talk, and Write
Main Idea What fights disease in the
human body?
Vocabulary A medicine that fights
bacteria in the body is called a(n)
______.
Classify How can diseases be
White blood cells of
the immune system
make antibodies to
fight invading
pathogens.
Treatments for
disease include
medicine, medical
technology, and
surgery.
Antibiotics help the
body fight bacteria,
but they become less
effective over years
of use.
Writing Link
classified into two groups? Give three
examples for each group.
Critical Thinking With every vaccine
there is a very small risk of infection.
Why are vaccines used anyway?
Test Prep Which is a rise in the
body’s temperature in response to
germs?
A antibody
B fever
C vaccine
D radiation
Test Prep To be sterile is to be
free of
all living things.
white blood cells.
germs.
air and water.
A
B
C
D
Social Studies Link
Interview an Expert
History Report
Interview a doctor or a nurse about
antibiotics. Ask which antibiotics they
use most often and which they use only
when necessary. Write a report to
discuss what you learned.
Research the discovery of the smallpox
vaccine by Edward Jenner. Be sure to
identify the kind of pathogen that
caused this disease. Present your
findings to the class.
91
EVALUATE
Use this glossary to learn how to pronounce and understand the
meanings of Science Words used in this book. Page numbers tell you
where to find words in the book.
Pronunciation Key
The following symbols are used throughout the Macmillan McGraw-Hill Science Glossaries.
a
ā
ä
âr
ô
at
ape
far
care
law
e
ē
i
ī
îr
end
me
it
ice
pierce
o
ō
ôr
oi
ou
hot
old
fork
oil
out
u
ū
.
u
up
use
rule
ū pull
ûr turn
hw
ng
th
th
zh
white
song
thin
this
measure
ә
about
taken
pencil
lemon
circus
' = primary accent; shows which syllable takes the main stress, such as kil in kilogram (kil' ә gram').
' = secondary accent; shows which syllables take lighter stresses, such as gram in kilogram.
aorta (ā ôr'tә ) The wide artery that leads out of the
heart. (p. 29) Blood travels through the aorta on its way
to the head, arms, or legs.
adolescence (ad'ә les'ә ns) The stage of growth that
begins at puberty and occurs between childhood and
adulthood. (p. 77) The body develops adult traits during
adolescence.
artery (är'tә rē) A blood vessel that carries blood away
from the heart. (p. 28) An artery throbs as blood rushes
through it.
adrenaline (ә dre' nә ’lә n) A hormone that is released
into the bloodstream in response to mental or physical
stress. (p. 68) Both excitement and fear can cause a
release of adrenaline.
axon (ak'sôn) The long part of a neuron that
carries impulses away from the cell
body. (p. 46) An impulse travels
as a wave down an axon.
alveoli (äl’vē ō’lī) Tiny air sacs in the lungs that exchange
gases with the blood. (p. 27) Air travels through tubes
that lead to alveoli.
antibiotic (an'tē bī ot’ik) A medicine that kills or slows
the growth of bacteria. (p. 88) Penicillin was the first
antibiotic.
antibody (an'ti bod’ē) A molecule in the immune system
that recognizes or attaches to a specific pathogen.
(p. 87) White blood cells can make an antibody against a
virus.
anvil (an'vә l) One of three tiny bones in the middle ear.
(p. 16) The anvil carries sounds from the hammer to the
stirrup.
92
GLOSSARY
B cell — cerebrum
calorie (kal'ә rē) A measurement of the amount of
energy in food. (p. 42) Foods in the grain group provide
many calories per serving.
B cell (bē sel) Special white blood cell that works with
T cells to make antibodies and to fight pathogens. (p. 87)
Each type of B cell recognizes a unique pathogen.
bladder (blad'ә r) Part of the excretory system, a sac
that holds urine. (p. 60) The bladder releases urine into
the urethra.
blood pressure (blud presh'ә r) The force of moving
blood against the inner walls of blood vessels. (p. 31)
Blood pressure that is too high can lead to heart disease.
capillary (kap'ә ler'ē) A short, thin, blood vessel that
delivers blood to body cells. (p. 27) A capillary connects a
small artery to a small vein.
carbohydrate (kär’bō hī'drāt) A nutrient that provides
energy for the body (p. 39) Starches and sugars are types
of carbohydrates.
cartilage (kär'tә lij) A firm, elastic body tissue that is a
part of the skeletal system. (p. 16) Parts of the ear, nose,
and trachea are made of cartilage.
cell body (sel bod’ē) The central part of a neuron.
(p. 46) Messages travel from the cell body down the
axon.
cell (sel) The basic unit of living matter, or tissue. (p. 4)
All living things are made up of cells.
central nervous system (sen'trә l nûr'vә s sis'tә m) Th
e brain and spinal cord. (p. 47) All nerves in the body
connect to the central nervous system.
cerebellum (sә r'ә bel' um) The part of the brain that
coordinates movement and controls balance and posture.
(p. 48) The cerebellum helps muscles work together to
move the body effectively.
brain stem (brān stem) The part of the brain that
connects to the spinal cord. (p. 48) The brain stem
automatically controls many body functions.
bronchi (brong' kī) A pair of tubes that branch off the
trachea and lead to the lungs. (p. 27) Bronchi connect the
lungs to the upper part of the respiratory system.
calcium (kal'sē ә m) A mineral
needed especially by bones and
teeth. (p. 39) Milk is a good
source of calcium.
cerebral cortex (sә rē' brel
surface of the cerebrum,
also known as gray
matter. (p. 48)
Thinking and
imagination
take place in
the cerebral
cortex.
kor'teks) The outer, folded
cerebrum
(sә rē' brum)
The part of the
brain where thought,
memory, and muscle
control take place. (p. 48) A
well-developed cerebrum allows
humans to be intelligent.
93
GLOSSARY
chemical digestion — epidermis
chemical digestion (kem'i kә l dī jes'chә n) The
chemical breakdown of food. (p. 38) Saliva in the mouth
begins chemical digestion.
diaphragm (dī'ә fram) A long, flat muscle that helps
move air in and out of the lungs. (p. 27) The size of the
chest changes as the diaphragm moves up and down.
chyme (chīm) A thick fluid into which food is changed
by the stomach. (p. 40) The stomach releases chyme into
the small intestine.
dietary fiber (dī'it âr’ē fī'bә r) Material from plants that
cannot be digested. (p. 38) Whole-grain cereals, fruits,
and vegetables are good sources of dietary fiber.
circulatory system (sûr'kyә lә tôr’ē
sis'tә m) The body system
responsible for moving blood
through the body. (p. 28) The
heart and blood vessels make
up the circulatory system.
communicable disease
(kә mū'ni kә bә l
di zēz') A
disease that can spread from
one person to another.
(p. 84) Covering your
mouth when you sneeze
can stop communicable
diseases from spreading.
compact bone (kom' pakt
bōn) The tissue that forms
the hard outer layer of
bones. (p. 19) Compact bone
gives the arm and leg bones the
strength they need.
dendrite (den'drīt) Tiny,
branch-like part of a neuron
that receives signals from other
cells. (p. 46) The end of a
neuron is lined with dendrites.
dermis (dûr'mīs) The layer of skin below the epidermis.
(p. 22) Nerve endings, blood vessels, and sweat glands
are part of the dermis.
diabetes (dīә bē'tēz) A disease caused by an inability to
make or use insulin properly. (p. 68) People with diabetes
often take shots of insulin.
dialysis (dī al' ә ’sis) A medical procedure that artificially
removes wastes from the blood. (p. 62) Dialysis takes
over the job of faulty kidneys.
94
GLOSSARY
digestive system (dī jes'tiv sis'tә m) The body system
that breaks down food into nutrients. (p. 38) The organs
of the digestive system form a long tube through the
body.
electrocardiogram (i lek’tro kär'dē o gram) A graphic
recording of heart muscle activity. (p. 32) Doctors can
detect heart disease by studying an electrocardiogram.
embryo (em'brē ō) The stage of human development
that begins shortly after an egg is fertilized. (p. 74) A
spine begins to form in the embryo.
endocrine system (en dô'krin sis'tә m) The body
system that makes and sends chemical messengers called
hormones. (p. 66) The thyroid, thymus, and pituitary
glands are organs of the endocrine system.
enzyme (en'zim) A type of protein in living things that
helps chemical changes take place. (p. 38) An enzyme in
the stomach helps break down proteins.
epidermis (ep’i dûr'mīs) The outer layer of the skin.
(p. 22) The epidermis sheds thousands of skin cells
every day.
esophagus — iodine
esophagus (i sof'ә gә s) The tube that carries food from
the mouth to the stomach. (p. 40) Chewing food
thoroughly allows it to pass through the esophagus.
heartbeat (härt'bēt’) One complete pulsation of the
heart. (p. 32) Your doctor can hear your heartbeats with a
stethoscope.
estrogen (es trō' gin) A female sex hormone that is
released by the ovaries. (p. 77) Estrogen signals female
traits to develop.
hemisphere (hem'ә sfîr’) The left or right half of the brain.
(p. 49) Different kinds of thinking take place in the left
and right hemispheres of the brain.
excretory system (ek skrә tôr'ē sis'tә m) The body
system that removes wastes. (p. 58) Kidneys are
important organs of the excretory system.
hemoglobin (hē mō' glōb in)
The material in red blood cells
that binds to oxygen and
gives blood its red color.
(p. 30) The blood’s
hemoglobin contains iron.
fetus (fē'tә s) The stage of development of a baby before
birth. (p. 74) A fetus develops all of the body systems
that a baby needs.
hormone (hôr'mōn) A
chemical messenger that
travels through the blood.
(pp. 6, 66) A hormone from
the pituitary gland controls
how the body grows.
immovable joint (i müv'ә bә l joint) A joint where no
motion occurs. (p. 18) The skull is an example of an
immovable joint.
immune system (i mūn' sis'tә m) The body system that
recognizes and fights specific pathogens. (p. 87) The
immune system uses special white blood cells to make
antibodies.
impulse (im'puls) The message of a single nerve, in the
form of an electrical signal. (p. 46) Impulses travel
through neurons to carry messages to, from, and within
the brain.
fever (fē'vә r) An abnormally high body temperature.
(p. 86) Fever helps the body fight infections.
glucose (glü' kōs) A type of sugar that cells use for
food. (p. 4) Blood carries glucose to every body cell.
infectious disease (in fek'shә s di zēz') A disease
caused by a pathogen, or harmful germ, that invades the
body. (p. 84) Colds, the flu, and strep throat are examples
of infectious diseases.
insulin (in'sә lin) A hormone from the pancreas that
controls the levels of sugar in the blood. (p. 68) Insulin
levels may be very high after a heavy meal.
integumentary system (in teg' yә men tә rē
sis'tә m) The body system that covers the body and
includes skin, hair, and nails. (p. 8) The integumentary
system acts as a first line of defense against germs.
hammer (ham'ә r) One of three tiny bones in the middle
ear. (p. 16) The hammer carries sound waves from the
eardrum to the anvil.
iodine (ī'ә dīn’) A chemical element that is used by the
thyroid to make hormones. (p. 69) Lack of iodine can
lead to an enlarged thyroid gland.
95
GLOSSARY
joint — nervous system
joint (joint) The place where two bones meet. (p. 18) The
elbow joint allows the arm to bend like a hinge.
keratin (ker'ә tin) A
tough, fibrous protein
that makes up hair and
nails. (p. 22)
Specialized skin cells
secrete keratin.
kidney (kid'nē) A
bean-shaped organ
that filters wastes
from the blood and
produces urine.
(p. 60) Tiny blood
vessels and
filtering tubes
make up a kidney.
mature (mә chür') Fully grown. (p. 78) The human body
is mature when it has stopped growing taller.
marrow (mâr'ō) Soft, fatty
tissue inside many bones.
(p. 19) Blood cells are
made by bone marrow.
mechanical
digestion (mi kan'i kә l
dī jes'chәn) The physical
process of breaking down
food into smaller parts.
(p. 38) The teeth begin
mechanical digestion of food.
menopause (men'ә pôz) The time in a woman’s life when
the menstrual cycle stops. (p. 78) Many women reach
menopause between the ages of 45 and 55.
menstrual cycle (men'strü ә l sī’kә l) A monthly cycle of
the female reproductive system. (p. 77) Many hormones
control the events of the menstrual cycle.
metabolism (mә tab'ә liz’ә m) The set of chemical
processes that occur in living things. (p. 42) Metabolism
gradually slows as the adult body ages.
large intestine (lärj in tes'tin) The wide tube at the
end of the digestive tract. (p. 40) Undigested parts of
food pass through the large intestine and out the body.
life cycle (līf sī’kә l) The stages of growth,
development, and reproduction of a species. (p. 74)
Childhood, adolescence, and adulthood are three stages
of the human life cycle.
ligament (lig'ә mә nt) Tough, rope-like tissue that
connects bones or cartilage at a joint. (p. 18) A ligament
may break if a bone is pushed too hard.
lipid (lip'id) A nutrient that is part of fat. (p. 39) The
body needs small amounts of many kinds of lipids.
liver (liv' ә r) A large, reddish-brown organ that treats
wastes and toxins so that the body can remove them.
(p. 58) Urea is a waste product made in the liver.
lymph (limf ) A pale fluid around body tissues that
contains white blood cells. (p. 30) A system of ducts
carries lymph around the body.
96
GLOSSARY
mineral (min'ә r ә l) A nutrient that helps the body’s
chemical processes. (p. 39) Iron, iodine, and calcium are
important minerals for the human body.
motor nerve (mō'tә r nûrv) A nerve that carries
messages from the brain to muscles or other body parts.
(p. 50) A muscle receives instructions through a motor
nerve.
muscular system (mus'kyә lә r sis'tә m) The body
system that moves bones and other body parts. (p. 20)
Exercise will build up the strength and flexibility the
muscular system.
nephron (nef'rôn) The filtering unit of the kidney. (p. 60)
The kidneys use millions of nephrons to filter the blood.
nervous system (nûr'vә s sis'tә m)
The body system responsible for thinking, remembering,
and carrying messages to and from body parts. (p. 46)
Nerves of the nervous system spread to nearly all body
parts.
neuron — reflex
neuron (nûr’rôn) A cell that carries messages in the
nervous system. (p. 46) A neuron may carry messages to,
from, or within the brain.
nutrient (nū’trē ә nt) A
material in food that the
body uses for energy or
to stay healthy. (p. 38)
Carbohydrates, vitamins,
and minerals are types of
nutrients.
organ system (ôr’gә n
sis'tә m) A set of organs
that work closely together
to meet one or more of
the body’s needs. (p. 6)
The lungs are part of an
organ system for
breathing.
ovaries (ō'vә rēz) The organs in women that produce
egg cells and female sex hormones. (p. 70) Ovaries
mature and begin working during adolescence.
over-the-counter medicine (ō'vәr thә
koun'tәr med'ә sin) A medicine that any adult may
purchase. (p. 88) Aspirin and cough syrups are popular
over-the-counter medicines.
placenta (plә ’sen'tә ) The organ that connects a
developing baby to the uterus of the mother. (p. 74) A
developing baby receives food and oxygen through
the placenta.
platelets (plāt'lets) Cell fragments in the blood that help
blood clot. (p. 30) Platelets clump together at the site of
a wound.
pregnant (preg'nә nt) To have a baby developing inside
the body. (p. 70) A woman is pregnant for about 9
months before the baby is born.
prescription medicine (pri skrip'shә n med'ә sin) A
medicine that can be obtained only by a doctor’s order.
(p. 88) A doctor orders a prescription medicine to treat
strep throat.
Town Drug Patient: Smith, Mary
123 Elm Street
Empire, NV 89405
(775)555-0123
Prescriber: Berman, J.S.
TAKE 1 TABLET UP TO 2 TIMES A DAY
AS NEEDED FOR DIZZINESS.
Meclizine, 12.5 mg tablets
Date filled: 08-24-2008
Quantity: 30 tablets
2 refills allowed
pathogen (path'ō jin) Any disease-causing germ,
including many bacteria and viruses. (p. 84) Three lines of
defense protect the body against pathogens.
protein (prō'tēn) A nutrient that helps body tissues
grow and repair themselves. (p. 39) Beans, meat, and fish
are good sources of proteins.
peripheral nervous system
(pә ri'
fu’rùl nûr'vә s sis'tә m) The nerves that lead into or out
of the brain or spinal cord. (p. 47)
Nerves in the arms and legs are
part of the peripheral nervous
system.
puberty (pū'bûr tē) The time at which adolescence
begins. (p. 77) Sexual traits begin to develop during
puberty.
pituitary gland (pi tü'ә
gland) A gland
that regulates much of
the endocrine system.
(p. 69) Hormones from
the pituitary gland affect
many other glands.
radiation (rā’ dē ā' shә n) A medical treatment that uses a
beam of energy to kill cancer cells. (p. 89) Radiation can
be used in combination with medicine and surgery to
treat cancer.
târ’ē
reflex (rē flecks') A body movement that occurs without
the involvement of the brain. (p. 51) Jerking a hand away
from a hot stove is an example of a reflex.
97
GLOSSARY
reproductive system — synapse
reproductive system (rē’prә duk'tiv sis'tә m) The body
system that allows adults to have children. (p. 70) Organs
of the reproductive system differ between men and
women.
resistant (ri zis’tә nt) Describes bacteria that cannot be
killed by antibiotics. (p. 90) Bacteria that are resistant to
penicillin have become more common.
respiratory system (res'pә r ә tôr’ē sis’tem) The body
system responsible for breathing. (p. 26) The lungs are
the main organs of the respiratory system.
spinal cord (spī'nә l kôrd) A thick bundle of nerves
held inside the spine. (p. 47) Nerves from the arms and
legs connect through the spinal cord to the brain.
sterile (ste'rùl) Free of disease-causing germs. (p. 89)
Surgery must be performed under sterile conditions.
sternum (stûrn' um) A flat bone that connects to the
ribs and protects the chest. (p. 16) The sternum helps
give shape to the chest.
stimulus (stim'yә lus) Any event that triggers a sensory
nerve. (p. 50) A stimulus can be interpreted as a sound,
sight, touch, taste, or smell.
stirrup (stûr'ә p) One of three tiny bones in the middle
ear. (p. 16) The stirrup works with the hammer and anvil
to carry sounds.
surgeon (sur’jen) A doctor who opens the body and
performs a surgery. (p. 89) A surgeon may be asked to
remove a diseased organ.
surgery (sûr'jә rē) An operation or procedure to remove,
repair, or replace a body part. (p. 89) Cancer patients
often need surgery to remove a tumor.
saliva (sәl i'vә ) A liquid that wets food in
the mouth and helps break it apart
both physically and chemically. (p. 40)
The smell of food can lead to the
mouth releasing saliva.
surgical operation (sûr'ji kә l op’ә rāsh'ә n) A medical
procedure performed by a surgeon that is used to treat
disease or repair the body. (p. 89) Cancer and other
diseases can be treated by performing a surgical
operation.
sensory nerve (sen'sôr’ē nûrv) A
nerve that carries messages into
or toward the brain. (p. 50)
Information from a sense organ
travels through a sensory nerve
to the brain.
serum (sîr'ә m) The liquid part of
blood. (p. 30) Glucose is carried
in the serum of the blood.
skeletal system (skel'i tùl
sis'tә m) A framework of bones
that shape and support the body.
(p. 16) Muscles move the skeletal
system at joints.
small intestine (smôl in tes'tin)
The long, narrow tube where most
chemical digestion takes place.
(p. 40) Nutrients are absorbed into
the blood by the lining of the small
intestine.
98
GLOSSARY
symptom (simp'tә m) A sign that a disease is present.
(p. 84) Pain and fever are symptoms of many diseases.
synapse (sin' aps) The tiny space between a neuron and
another cell, across which chemical messages travel.
(p. 47) Chemicals need a fraction of a second to travel
across a synapse.
T cell — villi
T cell (tē sel) A type of white blood cell that works
with B cells to make antibodies and to fight pathogens.
(p. 87) T cells help stop pathogens from invading more
than once.
urea (yûr'ē ә ) A waste material in
urine. (p. 58) Urea is made by the
liver and removed by the kidneys.
urinary system (yûr'i nâr’ē
sis'tә m) The part of the excretory
system that makes and removes
urine. (p. 58) Kidneys, the
bladder, and several tubes are
part of the urinary system.
urine (yûr'in) The liquid produced
by the kidneys to remove body
wastes. (p. 8) The bladder releases
urine from the body.
uterus (ū tә r'is) The organ in
women in which a baby grows and
develops. (p. 70) The placenta is
attached to the wall of the uterus.
tendon (ten'dә n) A tough, cord-like tissue that attaches
a muscle to a bone. (p. 20) A tendon pulls on a bone
when a muscle contracts.
testes (tes' tēz) The organs in men that produce sperm
cells and male sex hormones. (p. 70) Testes develop fully
during adolescence.
testosterone (tes'tôs’ tә r ōn) Male sex hormones that are
released by the testes. (p. 77) Testosterone causes the
voice to deepen.
thyroid (thī' roid) An endocrine gland in the neck that
affects how the body uses energy. (p. 69) A faulty
thyroid could cause feelings of tiredness or anxiety.
toxin (tok'sin) A poisonous substance in the blood.
(p. 58) The liver changes many toxins into harmless
wastes.
trachea (trā' kē ә ) The tube that carries air between the
throat and the lungs. (p. 26) A flap of tissue stops food
from entering the trachea.
transplant (trans plant') To transfer an organ from one
person’s body to another. (p. 62) A patient may have a
kidney transplant to replace faulty kidneys.
vaccine (vak sēn') A medicine that prepares the immune
system to fight a pathogen. (p. 87) The vaccine against
small pox has saved many lives.
vein (vān) A blood vessel that carries blood to the heart.
(p. 28) Blood from most body parts drains into two veins
that lead to the heart.
vertebrae (vûr'tә brā) Disk-shaped bones that make up
the spine. (p. 16) Lower vertebrae are thicker and wider
than upper vertebrae.
villi (vil'ī) Tiny
bumps that line
the wall of the
small intestine
and that absorb
nutrients into the
blood. (p. 40) Villi
act like a towel to
soak up nutrients.
99
GLOSSARY
vitamin — white blood cell
vitamin (vī'tә min) A nutrient that helps body cells work
properly. (p. 39) Fruits and vegetables are good sources
of many vitamins.
white blood cell (hwīt blud sel) One of many types
of cells that help fight infections. (p. 86) The body
responds to many diseases by making more white
blood cells.
100
GLOSSARY
Credits
The McGraw-Hill Companies, Inc. would like to acknowledge the artists and agencies who participated in illustrating this program: Argosy
and Four Lakes Colorgraphics.
Photography Credits: Front Cover (b)Dan McCoy/Rainbow/Getty Images, (l)Macmillan/The McGraw-Hill Companies; 2-3 F. Schussler/PhotoLink/Getty
Images; 3 (t)Macmillan/The McGraw-Hill Companies, (b)Richard Hutchings/Digital Light Source; 4 MM Productions/CORBIS; 5 Image Source;
6 (tc)Joe Polillio/Macmillan/The McGraw-Hill Companies, (tr bl bc bl)Macmillan/The McGraw-Hill Companies; 7 (tl br)Joe Polillio/Macmillan/The McGrawHill Companies, (tc tr)Macmillan/The McGraw-Hill Companies, (bl bc)Richard Hutchings/Digital Light Source; 8 Tracy Frankel/Getty Images; 9 (b)Kelly
Redinger/Design Pics/CORBIS, (t)Macmillan/The McGraw-Hill Companies; 10 (t to b)Stockbyte/PunchStock, (2)Al Telser/Macmillan/The McGraw-Hill
Companies, (3)Jim Wehtje/Getty Images, (4)Stockdisc/PunchStock; 11 (t to b)MM Productions/CORBIS, (2)Macmillan/The McGraw-Hill Companies,
(3)Richard Hutchings/Digital Light Source, (4)Tracy Frankel/Getty Images; 12 (t)Blend Images, (b)Randy Faris/CORBIS; 13 Dynamic Graphics/
Jupiterimages; 14-15 Louis Fox/Getty Images; 15 Richard Hutchings/Digital Light Source; 16 Dynamics Graphics Group/Creatas/Alamy; 17 Richard
Hutchings/Digital Light Source; 18 Brand X/CORBIS; 19 Images-USA/Alamy; 20 (c)Alistair Berg/Getty Images, (bl)Innerspace Imaging/Photo Researchers,
Inc., (bc)Carolina Biological Supply Company/Phototake, (br)Innerspace Imaging/Photo Researchers, Inc.; 21 (t)Richard Hutchings/Digital Light Source,
(b)Steven Errico/Getty Images; 22 (l)Macmillan/The McGraw-Hill Companies, (r)Bananastock; 23 (tl)Richard Hutchings/Digital Light Source,
(cl)Innerspace Imaging/Photo Researchers, Inc., (bl)Macmillan/The McGraw-Hill Companies; 24-25 Anatomical Travelogue/Photo Researchers;
25 Macmillan/The McGraw-Hill Companies; 26 Duomo/CORBIS; 27 Macmillan/The McGraw-Hill Companies; 28 Macmillan/The McGraw-Hill Companies;
30 (l)Al Telser/Macmillan/The McGraw-Hill Companies, (r)Comstock/CORBIS; 31 (tl)Don Farrall/Getty Images, (cr)Richard Hutchings/Digital Light Source;
32 (t)Hans Neleman/Getty Images, (b)Peter Widmann/Alamy; 33 (t)Duomo/CORBIS, (b)Comstock/CORBIS; 34 Bettmann/CORBIS; 35 (t)Bruce Ayres/
Getty Images, (b)Hank Morgan/Photo Researchers, Inc.; 36-37 Susumu Nishinaga/Photo Researchers; 37 Macmillan/The McGraw-Hill Companies;
38 PNC/Digital Vision/Getty Images; 39 (tl)Ingram Publishing/Alamy, (tr)Ingram Publishing/SuperStock, (cl)Ernie Friedlander/Cole Group/Getty Images,
(c)Alan Richardson/Stockfood Creative/Getty Images, (cr)D. Hurst/Alamy, (bl)Image Source/Getty Images; 40 Joe Polillio/Macmillan/The McGraw-Hill
Companies; 41 (l)Dr. Richard Kessel and Dr.Gene Shih/Visuals Unlimited, (r)Joe Polillio/Macmillan/The McGraw-Hill Companies; 42 liquidlibrary/
PictureQuest; 43 (tl)PNC/Digital Vision/Getty Images, (cl)Joe Polillio/Macmillan/The McGraw-Hill Companies, (bl)liquidlibrary/PictureQuest; 44-45 Dan
McCoy/Rainbow/Getty Images; 45 (t)Richard Hutchings/Digital Light Source, (b)Joe Polillio/Macmillan/The McGraw-Hill Companies; 46 Royalty-Free/
CORBIS; 47 Macmillan/Mcgraw-hill Companies; 49 (t)BSIP/Photo Researchers, (b)Dex Image; 50 Macmillan/The McGraw-Hill Companies; 52 (l)Comstock
Images/Jupiterimages Corporation, (r)Lawrence M. Sawyer/Getty Images; 53 (tl)Royalty-Free/CORBIS, (cl)Macmillan/The McGraw-Hill Companies;
54-55 AP Photo/Tsunemi Kubodera of the National Science Museum of Japan, HO; 55 Anup Shah/Photodisc/Getty Images; 56-57 Dr. Dennis Kunkel/
Visuals Unlimited; 57 Macmillan/The McGraw-Hill Companies; 58 David R. Frazier Photolibrary, Inc./Alamy; 59 Macmillan/The McGraw-Hill Companies;
60 Dr. Dennis Kunkel/Visuals Unlimited; 61 Science Photo Library/Photo Researchers; 62 AJPhoto/Photo Researchers; 63 (tl)David R. Frazier
Photolibrary, Inc./Alamy, (tcl bcl)Dr. Dennis Kunkel/Visuals Unlimited, (bl)AJPhoto/Photo Researchers; 64-65 Jim Cummins/Getty Images; 66 Gary
Caskey/Reuters/CORBIS; 67 (tl)Ken Cavanaugh/Macmillan/The McGraw-Hill Companies, (tr)Richard Hutchings/Macmillan/The McGraw-Hill Companies;
68 (t)Stockdisc/PunchStock, (b)Ron Fehling/Masterfile; 69 (t)Macmillan/The McGraw-Hill Companies, (b)Royalty-Free/CORBIS, (br)Scott Camazine/
Photo Researchers, Inc.; 70 BananaStock/PictureQuest; 71 (tl)Gary Caskey/Reuters/CORBIS, (cl)Ken Cavanaugh/Macmillan/The McGraw-Hill Companies,
(cl)Ron Fehling/Masterfile, (bl)BananaStock/PictureQuest; 72-73 Paul Barton/CORBIS; 73 Richard Hutchings/Digital Light Source; 74 Brand X Pictures/
PunchStock; 75 (t)Don Tremain/Getty Images, (b)Cydney Conger/CORBIS; 76 IT Stock/PunchStock; 77 (l)Jupiterimages/BananaStock/Alamy Images,
(c)George Doyle and Ciaran Griffin/Getty Images, (r)Amana Images, Inc./Alamy Images; 78 Royalty-Free/Masterfile; 79 (tl)Brand X Pictures/PunchStock,
(cl)Amana Images, Inc./Alamy Images, (cl)IT Stock/PunchStock, (bl)Royalty-Free/Masterfile; 80 (t)Royalty-Free/CORBIS, (b)Photodisc Collection/Getty
Images; 81 Dynamic Graphics/Jupiterimages; 82-83 Dennis Kunkel/Phototake; 83 (t)Macmillan/The McGraw-Hill Companies, (b)Richard Hutchings/Digital
Light Source; 84 Scott Camazine/Photo Researchers, Inc.; 85 (l)James Leynse/CORBIS, (r)Kevin A. Somerville/PHOTOTAKE, Inc./Alamy Images;
86 Dr. Fred Hossler/Getty Images; 88 (t)Image Source/CORBIS, (b)Royalty-free/CORBIS; 89 Royalty-free/CORBIS; 90 (l)Bettmann/CORBIS, (r)Hank
Morgan/Science Photo Library; 91 (tl)Scott Camazine/Photo Researchers, Inc., (cl)Royalty-free/CORBIS, (bl)Bettmann/CORBIS; 93 (cl)Don Farrall/Getty
Images, (bl)D. Hurst/Alamy; 94 (tr)Alan Richardson/Stockfood Creative/Getty Images, (l b)Macmillan/The McGraw-Hill Companies; 95 (r)Comstock/
CORBIS, (l)Brand X Pictures/PunchStock; 96 Dr. Dennis Kunkel/Visuals Unlimited; 97 (t)PNC/Digital Vision/Getty Images,(b)Royalty-Free/CORBIS;
98 (l)Digital Light Source/Richard Hutchings, (r)Royalty-free/CORBIS; 99 (t)Macmillan/The McGraw-Hill Companies, (b)Dr. Richard Kessel and Dr. Gene
Shih/Visuals Unlimited; 100 (t)Ingram Publishing/SuperStock, (b)Dr. Fred Hossler/Getty Images.
101
CREDITS