4 5 fighting infections (life science)

Extended Vocabulary antibody antigen lymphocyte lysozyme noninfectious disease phagocyte tonsillitis Vocabulary immune system infectious disease involuntary muscles neuron pathogens vacc

Scott Foresman Science 4.5

Nonfi ction Draw Conclusions • Captions

• Text Boxes

• Call Outs

• Glossary

Body Systems

ISBN 0-328-13873-8

ì<(sk$m)=bdihdj< +^-Ä-U-Ä-U

Scott Foresman Science 4.5

Nonfi ction Draw Conclusions • Captions

• Text Boxes

• Call Outs

• Glossary

Body Systems

ISBN 0-328-13873-8

ì<(sk$m)=bdihdj< +^-Ä-U-Ä-U

1 What is your body’s fi rst defense against

pathogens?

2 How do white blood cells fi ght infections?

3 How do vaccines protect you from

infections?

4 E coli is one kind of

bacteria that causes food poisoning

Describe how E coli attacks the body

Include details from the book to support your answer

5 Draw Conclusions Why do you think

vaccines are given to children when they are young?

What did you learn?

Extended Vocabulary

antibody antigen lymphocyte lysozyme noninfectious disease phagocyte

tonsillitis

Vocabulary

immune system

infectious disease

involuntary muscles

neuron

pathogens

vaccine

voluntary muscles

Picture Credits

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The publisher deeply regrets any omission and pledges to correct errors called to its attention in subsequent editions.

Photo locators denoted as follows: Top (T), Center (C), Bottom (B), Left (L), Right (R), Background (Bkgd).

2 (BL) Kent Wood/Photo Researchers, Inc.; 3 Ryabchikova-Voisin/Photo Researchers, Inc.;

7 (TL, B, CR, CL) American Museum of Natural History/DK Images; 11 (CR) NIH/Science Source/Photo Researchers, Inc;

12 (B) American Museum of Natural History/DK Images; 13 (T) American Museum of Natural History/DK Images;

16 (B) American Museum of Natural History/DK Images; 17 (T) American Museum of Natural History/DK Images;

18 American Museum of Natural History/DK Images.

Unless otherwise acknowledged, all photographs are the copyright © of Dorling Kindersley, a division of Pearson

ISBN: 0-328-13873-8

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3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

by Steve Miller

Your body is made of many kinds of cells that do

different jobs Cells make up tissues Tissues of different

kinds work together as organs Organs include your

heart, your lungs, your bones, and even your skin

A group of organs work together as an organ system

The shape of your body comes from the skeletal

system, which is made of 206 bones The muscular

system allows your bones to move Voluntary muscles

are the ones that you control when you decide to walk,

run, or climb Muscles that you can’t control are called

involuntary muscles These are the muscles used for

breathing, digestion, and blood fl ow

The respiratory system brings oxygen into your body

and removes carbon dioxide The circulatory system

brings oxygen and

nutrients to your

cells and takes

away carbon

dioxide and

other waste

What You Already Know

2

This is a virus under

magnifi cation.

The digestive system breaks food down into nutrients that your cells need The nervous system controls the other organs and systems Its two main parts are the brain and the spinal cord Nerves are groups of neurons that carry messages between the brain and other organs

Organisms such as bacteria and viruses that cause disease are called pathogens When they get inside your body, they can destroy cells or change the way the cells work The immune system protects your body from these pathogens

A disease that can be transferred from one organism

to another by pathogens is called an infectious disease

One kind of infectious disease is the common cold

A vaccine is a medicine that helps your immune system

fi ght pathogens The vaccine helps the immune system identify the disease quickly The immune system is then able to fi ght the disease faster

Your immune system may face many kinds of pathogens and diseases Let’s fi nd out about some of these invaders and how your body fi ghts against them

3

Diseases

You can see that the girl in the photo does not feel

well She is wrapped in a blanket to fi ght a chill The

thermometer in her mouth is checking for a fever If you

have ever had a bad cold, you know these symptoms

Sometimes parts of the body have a disease When

this happens, these parts cannot perform their normal

functions Some diseases are inherited Some are caused

by exposure to toxic chemicals Still other kinds of

diseases are caused by organisms that invade your body

Many illnesses, such as cancer or heart disease, are

noninfectious diseases You cannot get sick just from

being close to someone with a noninfectious disease

This is a cold virus under magnifi cation.

5

Infectious diseases, such as colds, the fl u, and chicken pox, can be passed from one person to another These illnesses are caused by microorganisms that invade your body When you are around someone who has

an infectious disease, the organisms that he or she has can travel to your body The human body has a strong defense system to protect itself from these disease-causing organisms

A cold is an infectious disease that causes chills, fever, and tiredness.

Bacteria and Viruses

Pathogens are organisms that cause disease Many

common pathogens are too small to see They include

bacteria and viruses When these pathogens get inside a

body, they can destroy cells or change the way cells work

Bacteria are one-celled organisms They are

very small—as many as one thousand

bacteria could form a line across the head

of a pin Most bacteria are harmless

and live inside your body all the

time Other bacteria are pathogens

When these bacteria invade, they

reproduce very quickly Sore throats,

ear infections, and tonsillitis are

often caused by bacteria

Viruses are much smaller than

bacteria They don’t have cells of

their own Some viruses enter the

cells of the body and take over their

functions Diseases caused by viruses

include measles, chicken pox, and

the common cold

Coughs and sneezes can send pathogens through the air, from one person to another.

7

These shigella bacteria are found in contaminated water They can cause fever, diarrhea, and nausea.

This is a model of one kind

of virus Viruses have very small, simple structures compared to cells

Outer Defenses

Your body can protect itself from pathogens The

best way to stay healthy is to keep pathogens out of your

body in the fi rst place This is the job of the largest organ

of your body—your skin Skin covers the other organs

and keeps many harmful organisms out

When the skin is scraped or cut, there is

an opening It is important to keep skin

wounds clean and covered to prevent

infections

Your body has natural openings

in the skin, such as your eyes, nose,

and mouth To protect them from

bacteria, your body produces

a chemical called lysozyme

Lysozyme destroys the cell walls

of some bacteria It is found in

sweat, the liquid that your body

uses to cool your skin Lysozyme

is also produced in mucous

membranes, which are the soft

tissues inside your mouth and

The fi rst protection against pathogens is the skin.

9

The fl uid produced by tear ducts has chemicals that kill bacteria.

Tonsils are found at the back of your throat They can produce substances that help fi ght respiratory disease, but they can also become infected If your tonsils have an infection, you have tonsillitis Some symptoms of tonsillitis are

a sore throat, diffi culty swallowing, and a fever.

Tonsils

Tear ducts make the

fl uid that keeps your eyes from becoming too dry

Tear ducts add lysozyme

to the fl uid to kill bacteria that land on the surface of your eye

Vitamin A is needed for your body

to produce lysozyme Without vitamin A, eyes are more likely to be affected by bacterial diseases

White Blood Cells

When pathogens get into the body, the immune

system fi ghts them White blood cells are part of the

immune system’s defense They are part of the blood,

so they fl ow to nearly every part of the body Phagocytes

are one kind of white blood cell They rush to the site

of infection They are produced in marrow, which is

the tissue inside bones When a phagocyte fi nds a

bacterium or other pathogen,

it surrounds the enemy

and digests it Some

phagocytes are able to

squeeze through very small

gaps between cells This allows

them to get into organs and attack

invaders throughout the body

Phagocytes can send out “arms” that surround bacteria so they can be destroyed.

white blood cell

11

Why do people get sick if they have phagocytes

to fi nd and destroy pathogens? Some kinds of bacteria have coatings that can trick the white blood cells for a while The coating on the outside of the cell makes the pathogen appear to be harmless This trick allows the

invader to reproduce and spread to many parts of the body before

it is detected

bacteria

Your body has billions of red and white blood cells

Antigens are molecules covering the surface of a cell

They give the cell a unique set of characteristics White

blood cells can recognize antigens White blood cells

called lymphocytes fi ght infections T cells and B cells

are two kinds of lymphocytes T cells determine what

antigen is on a cell If the immune system recognizes the

antigen as harmful, the helper T cell sends out a signal

The B cell uses this signal to identify the danger

Antibodies

Different types of white blood cells work together

to fi ght pathogens.

Helper T cell identifi es antigens on bacteria.

A bacterium

is engulfed

by a white

blood cell.

B cell recognizes messages from helper cell.

13

The B cell turns into a plasma cell It then makes another chemical, called an antibody, which attaches to the antigen The antibody then attacks the pathogen

There are many different antibodies Each one marks and protects the body from a specifi c pathogen

Because the immune system remembers antigens,

it can respond faster the second time it encounters an infection Some diseases occur only once If you had chicken pox when you were two years old, you are not likely to ever get it again

B cell turns into a plasma cell and releases antibodies.

Antibodies mark bacteria.

Vaccinations

Lymphocytes use only antigens to identify an

organism as harmful or safe Your body defeats many

kinds of bacteria by forming antibodies Some bacteria,

however, are too strong for your body to defeat on its

own Doctors inject a vaccine into your body to help

fi ght some infections A vaccine is made from a dead

or weak form of a pathogen

Some of the most dangerous

infectious diseases have been

controlled by vaccinations.

15

The weak pathogen in a vaccine causes the body to make antibodies that work against the harmful pathogen.

Vaccines are usually given to children when they are young When you are injected with a vaccine, your body recognizes that it is something that does not belong

The immune system makes antibodies to remove it

The immune system can remember disease-causing organisms If you are exposed to the disease later, your immune system recognizes it right away Antibodies are available quickly The bacteria or virus is removed as if you had already had the disease

The fi rst vaccine was produced by an English doctor, Edward Jenner, in 1796 He did many experiments to

fi nd out how smallpox could be prevented Smallpox was a fatal disease in the 1700s Jenner’s experiments led to the fi rst vaccine against smallpox

vaccine

antibody

destroyed pathogen harmful

pathogen

Coughs and Colds

Some illnesses are very common One common

disease is a sore throat caused by bacteria One

symptom of this bacterial infection is white or yellow

spots on the back of the throat Streptococcus

(strep-tuh-KAH-kuhs) bacteria are often the cause,

so you may hear the disease called strep throat

Your doctor might give you antibiotics to help

you fi ght this infection

The most common of all illnesses is a cold Colds

are caused by viruses Everyone knows what happens

when cold viruses get into the body—coughing,

sneezing, runny nose, and generally not feeling well

There is no vaccination to prevent colds because there

are so many different viruses that cause them

These streptococcus bacteria can cause a painful infection

in your throat.

17

Infl uenza, also called the fl u, is another disease caused by viruses It is similar to a very bad cold

Because the fl u can be more dangerous than a cold, doctors often recommend vaccination New kinds

of fl u viruses develop frequently, so the fl u vaccine from last year may not protect you this year

There are many different kinds of adenoviruses—the cause of the common cold.

A fever is part of your body’s defense system

Many pathogens are harmed or reproduce more slowly at higher temperatures The fever gives the immune system time to make more white blood cells to fi ght

these pathogens.

Fevers

Food Poisoning

Food is a common way for bacteria and viruses to get

past your body’s defenses Most of the time, strong acids

and other chemicals in your stomach kill any harmful

bacteria in your food Sometimes, however, harmful

bacteria pass through the stomach and multiply rapidly

in the intestines Millions of people in the United States

get sick each year by eating contaminated food Although

most cases are mild, food poisoning sometimes causes

serious health problems

E coli bacteria from contaminated

food stick to the wall of the intestines.

E coli bacteria

19

E coli bacteria that are common in meats that are not

completely cooked and on the surface of raw vegetables and fruits cause one infection Chemicals on the surface

of these E coli damage the

lining of the intestines

Another common illness caused by food is salmonella poisoning Salmonella

bacteria live in eggs and raw meat and sometimes on unwashed fruit

Covering and refrigerating food slows the growth of bacteria and reduces the chance of food poisoning

Bacteria release harmful toxins that attack the wall.

Avoiding Infection

You can avoid infections by keeping your body

healthy and by avoiding germs One of the best things

you can do is wash your hands often Many pathogens

enter your body when you touch your eyes, nose, or

mouth Wash your hands with soap before you eat,

after you use the bathroom, and whenever you touch

something used by a person who is sick You can also

protect yourself by keeping your home and body clean,

so that bacteria don’t have a place to grow

You can protect yourself from food infections

by using care in your kitchen Wash fresh fruits and

vegetables before eating them Always be sure that meats

and eggs are completely cooked, because heat kills bacteria

Wash all surfaces that have touched raw meat right away

Researchers have found that washing hands with soap is the most effective way to keep pathogens out of your body.

21

In order to make you sick, the pathogens need to get into your body A cut or scrape is a way for germs to get past your skin You can help your skin protect you

by cleaning cuts and scrapes right away Keeping the cut covered with a bandage protects the wound while

it heals

Covering cuts and scrapes helps keep infections from occurring at skin openings.

Because they treat people who have pathogens in their bodies, doctors and nurses must be careful to avoid spreading disease

Surgical masks and gloves protect patients from infection After use, each instrument and tool

is sterilized by heat or chemicals to kill

all pathogens

Hospital Hygiene