27- 2 Body Defenses
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Your body is under constant attack by pathogens. If
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pathogens are not destroyed or prevented from entering
your body, you may become ill or get/an infection. Your
body, however, has two lines of defe se that protect you
against most pathogens.
The skin and the mucus and .;
cilia of the respiratory system
are the body's first line of
defense against disease.
White blood cells are the
body's second line of defense
against disease.
FIRST LINE OF DEFENSE
Natural immunity is present
from birth. Acquired immunity
is developed during the lifetime
of a person.
Your skin is the body's first line of defense. In fact, if
your skin is not broken, it is almost gbrm-proof. The
perspiration, or sweat, made by the sf-in contains'
substances that slow or kill bacteria. 'For example, salts in
perspiration help prevent the growthl of bacteria on the '
skin. Oils and waxes produced by the skin also help keep
out pathogens.
Body openings, such as your mouth and nose, are
places where pathogens can enter your body. However,
other first-line defenses prevent pat' operis frorn entering
body openings. For example, hair~ in your nose filter air
and stop many pathogens. Tiny hairlike cilia (SIL-ee-uh)
and mucus in your respiratory systefu trap pathogens
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before they can enter the lungs. Mucus also contains
substances that kill pathogens. Sneezing and coughing
help remove pathogens from the body.
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Figure 27-3
This
phagocyte is destroying a
foreign substance in the
blood.
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SECOND LINE OF DKFENSE '
vvhat happens when pathogensget through your body's
first line of defense? Then, special "vpite blood cells,
,
called phagocytes (FAG-uh-syts), go to work. Phagocytes
are shapeless cells that .move like adoe.bas. Phagocytes
also feed like amoebas. These White/ blood cells can
surround pathogens and destroy them.
.
.6. Some phagocytes can leave the bllood and ~ove to
infected areas. These cells are called leucocytes
(LOO-koh-syts). If you have ever ham an infect d cut on
your finger, you have seen the work/ of Ieucocj tes. During
an infection, leucocytes kill pathogens at the site of the
infection. The finger may feel hot t9 the touch, look red,
and be very sord. Pus forms at the s~te of the infection.
Pus is made out of dead pathogens, read leucocytes, and
Hurnan Health
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plasma, the liquid part of the blood. How would you know
that your leucocytes were working properly if you had an
infected cut on your finger?
Chemical Defenses
A chemical defense S'ystem also protects Y01,lf body against
disease. The immune system ·control~· the body's chemical
·--·defenses.
The immune system is--rna:ae up, q(cells'and
tissues that identify and kill pathogens.
Health and Safety Tip
YOUI should always wash a
wound and apply an
antiseptic. An antiseptic is a
subltance that helps prevent
infettion,
•.
You may wish to tell students that the
reaction of the human body against an .
antigen is called an immune response.
Interferon
A chemical called interferon (in-tur-FEER-ahn) is made
by cells when a virus invades the body. Interferon slows or
stops viruses from reproducing. Unlike antibodies,
interferon attacks all viruses. Howevervinterferon made
by one kind of organism cannot be used by another kind
of organism. If you are infected by a virus, only human
interferon will help you fight off the disease. Today,
scientists use genetic-engineering
techniques to make
human interferon.
Lntibodies
and Antigens
What happens when a pathogen enters your body? Your
body immediately recognizes that a foreign substance, or
antigen (AN-tuh-jun), is in the body. For example, an
antigen may be the capsid, or protein coat, ora virus. The
body responds to the antigen by producing antibodies. An
antibody is a protein made by your body to fight off a
specific antigen.
Antibodies fit a specific antigen like two pieces of a
jigsaw puzzle. Once the antibody connects to the antigen,
special white blood cells engulf the pathogens.
Antibody
You may wish to tell ~~~~.~nts
that the
whitelblood cells that engulf the
antibody and antigen are called
macrophages. Figure 27-3 shows a
macro hage.
Figur1e27-4
An antigen
anda~ antibody fit together
like pieces of a jigsaw puzzle.
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Drseases
481
Immunity
When a person has resistance to a specific disease, that
person has immunity (im-MYOON-i-teej. You have two
kinds of immunity, natural immunity and acquired
(uh-KWY -urd] immunity. Natur~~ immunity is your
body's natural defense against certain diseases. In fact,
you are born with natur~l immunity to many diseases that
infect other organisms.. ":
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There are several ways of acquiring immunity, You
can be injected with a serum. A ~erum is a substance that
contains antibodies against a certain disease. Serums,
however, provide only temporary immunity.
~ One kind of acquired immunity is called passive
immunity. Passive immunity is acquired when you are
injected with antibodies against a certain disease. Passive
immunity also can be acquired bly a developing baby. The
developing baby receives antibodies from its mother. Why
do you-think that this kind of imkunity is not called
'1 .
it ? The baby did not produce the
na t ura imrnuru y. antibodies, (Applying concepts)
Once you have been exposedj to some diseases, your
body continues to make antibodi1es against those diseases. '
This kind of immunity is called active
immunity. Active
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immunity usually is permanent. Have you ever had the
mumps? If you have, you now h~ve active immunity
against the mumps ..
Another way to get active immunity is to get vaccine.
Most vaccines are made from dead'or weakened bacteria
or viruses. Vaccines, however, db not cause you to get the
disease.When you get a vaccine kor measles, your body
begins to produce antibodies against the measles virus.
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Skill Builder
Researching Smallpox,
measles, and polio are three
diseases for which vaccines
have been developed. Write a
brief report about the
development of one of these
vaccines. How has the .:'
vaccine been beneficial to
society?
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Figure 27-5
A vaccine
will help protect this child
against the measles virus.
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These antibodies remain in the body and protect you from
future infections of the measles virus.
Drugs also have been developed to help your body
fight pathogens. For example, infections caused by bacteria
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often are treated with antibiotics (an-ti-by-AHT-iks).
Antibiotics are chemical substances that kill bacteria or
prevent the reproduction of bacteria. Some antibiotics are
made from fungi or bacteria. Three widely used
antibiotics are penicillin, streptomycin, and tetracycline.
Sulfa drugs also are used to fight disease. Doctors often
prescribe sulfa drugs to fight bacterial infections of the
digestive and urinary systems.
Health and Safety Tip
Ta1e antibiotics and sulfa
dru~s only when they are
prescribed by a doctor.
Antibiotics can cause skin
ras~es or upset stomach in
so e people.
You may wish to tell students
hac rria can become resistant
anti Jiolics,
that sorno
to
Think and Discuss
6. What is an antigen?
7. How does an antibody fight disease?
8. How d~es the skin help protect your body against
disease?
9. What is the difference between natural and
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acquired immunity?
10.
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Why do surgeons wear masks and gloves during
operations?
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27 -3
Chronic Disorders
Some illnesses may last for a long time or can reoccur.
These illnesses are called chronic disorders. Allergies,
hepatitis (hep-uh- TYT-is], and cancer are examples of
chronic disorders.
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Cancer, allergies, and hepatitis
are three chronic disorders,
Do you know someone who sneezes or develops watery
eyes if they come in contact with a certain plant or
animal? This person probably suffers from an allergy
(AL-ur-jee). An allergy is an abnormal reaction to a
substance in the environment.
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Any substance that causes an allergy is called an
allergen (AL-ur-jun). Common allergens include plant
pollen, pet dandruff, and household dust. Ha1 fever is an
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Diseases and Disorders
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