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Section 21.2 Defenses Against Disease
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Section 21.2 Defenses Against Disease
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Section 21.2 Defenses Against Disease
Write the letter of the correct answer using
the list on the right.
1. Organisms such as yeasts, molds, and
mushrooms.__________
2. Single-celled organisms that are much
larger and more complex than
bacteria. __________
3. Simple, single-celled microorganisms.
________
4. Microorganisms and viruses that
cause disease. _______
5. The smallest pathogens._______
a.
b.
c.
d.
e.
f.
Pathogens
Bacteria
Toxins
Fungi
Protozoan
Viruses
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Section 21.2 Defenses Against Disease
Decide whether each statement is true or false.
6. Some infectious diseases are transmitted to humans through the
bites of animals. _________
7. An infected person cannot spread a disease to another person.
_______
8. Pathogens can cause an infectious disease when they enter your
body and multiply. ________
9. It is important to refrigerate food promptly to prevent the growth of
harmful bacteria. ________
10. All pathogens die immediately when they leave a person’s
body.________
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Section 21.2 Defenses Against Disease
Defenses Against Disease
Objectives
Identify the body’s physical and chemical
defenses against infectious disease.
Describe the inflammatory response.
Summarize how the immune system works.
Compare passive and active immunity.
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Section 21.2 Defenses Against Disease
Quick Quiz Complete each of these statements with always,
sometimes, or never.
I ____ wash my hands before meals.
When preparing fruits and vegetables, I ____ wash
them thoroughly.
I am ____ careful to use only my own eating utensils,
drinking cups, towels and grooming items.
I ____ cover my mouth when I cough or sneeze.
If I spend time in wooded areas, I ____ wear
insect repellent.
For each of your responses, explain how your behavior
could affect your chances of getting or spreading an
infectious disease.
Switch to QuickTake version of the quiz.
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Section 21.2 Defenses Against Disease
Physical and Chemical Defenses
Your body’s first line of defense against infectious
disease includes both physical and chemical defenses
that prevent pathogens from entering your body.
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Section 21.2 Defenses Against Disease
Skin
• Your skin serves as both a physical and a chemical
barrier against pathogens.
• Sweat acts as a chemical barrier.
• Old skin cells are shed constantly, and the
pathogens on these cells are shed, too.
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Section 21.2 Defenses Against Disease
Mucous Membranes
• The openings into your body, such as your mouth,
eyes, and nose, are covered by protective linings
called mucous membranes (MYOO kus).
• Mucus traps many pathogens and washes
them away.
• Mucus contains chemicals and specialized cells that
attack pathogens.
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Section 21.2 Defenses Against Disease
Cilia
• Some of your body’s mucous membranes are lined
with tiny hairlike structures called cilia (SIL ee uh).
• Together, cilia and mucus help trap and
remove pathogens.
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Section 21.2 Defenses Against Disease
Saliva and Tears
• Your saliva and tears can trap pathogens and wash
them away.
• Saliva and tears also contain chemicals that attack
pathogens.
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Section 21.2 Defenses Against Disease
Digestive System
• Chemicals in your digestive system kill
many pathogens.
• The normal motions of the digestive system move
pathogens out.
• Bacteria that normally live in your digestive system
produce substances that can harm or kill
invading bacteria.
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Section 21.2 Defenses Against Disease
Your Body’s Physical and Chemical Defenses
5)
1)
2)
3)
4)
Stomach
Saliva andacid
tears
When
certain
Saliva you
and swallow
tears can
wash pathogens
with
water,
or mucus, acids in your
awayfood,
some
pathogens.
stomach can kill those pathogens.
1
Mucous membranes
Mucus traps some pathogens,
preventing them from entering
your body.
Cilia
Cilia help move mucus
and pathogens out of
your body when you
cough or sneeze.
Skin
Your skin is an effective barrier
against many pathogens.
2
3
4
5
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Section 21.2 Defenses Against Disease
Inflammation
• Inflammation (in fluh MAY shun) is your body’s
general response to all kinds of injury, from cuts and
scrapes to internal damage.
• Inflammation fights infection and promotes the
healing process.
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Section 21.2 Defenses Against Disease
Phagocytes
• Within seconds after your body is injured, the
damaged cells release chemicals that cause blood
vessels in the injured area to enlarge.
• Blood, other fluids, and white blood cells called
phagocytes (FAG uh syts) leak out of the
enlarged vessels.
• Phagocytes engulf and destroy pathogens.
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Section 21.2 Defenses Against Disease
Phagocytes
This micrograph shows a phagocyte (blue) attacking
bacteria (pink). Phagocytes kill pathogens by
engulfing and then digesting them.
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Section 21.2 Defenses Against Disease
Healing
• Phagocytes also give off substances that cause
healing to begin.
• The inflammation process heals the damage, and the
inflammation subsides.
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Section 21.2 Defenses Against Disease
The Immune System
The immune system (ih MYOON) fights disease by
producing a separate set of weapons for each kind of
pathogen it encounters.
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Section 21.2 Defenses Against Disease
The Immune Response
• When a pathogen enters your body for the first time,
it often causes disease.
• White blood cells called lymphocytes (LIM fuh syts)
carry out most of the immune system’s functions.
• If a pathogen that has previously attacked your body
enters your body again your immune system will
quickly recognize the pathogen and launch an
immediate attack.
• Immunity (ih MYOON ih tee) is your body’s ability to
destroy pathogens that it has previously encountered
before the pathogens are able to cause disease.
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Section 21.2 Defenses Against Disease
T Cells
T cells perform several functions.
• Killer T cells destroy any body cell that has been
infected by a pathogen.
• Helper T cells produce chemicals that stimulate
other T cells and B cells to fight off infection.
• Suppressor T cells produce chemicals that “turn
off” other immune system cells when an infection
has been brought under control.
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Section 21.2 Defenses Against Disease
B Cells
• The B lymphocytes, or B cells, produce antibodies.
• Antibodies (AN tih bahd eez) are proteins that
attach to the surface of pathogens or to the toxins
produced by pathogens.
• This binding action keeps the pathogen or toxin from
harming the body.
• The memory capacity of B cells explains why you
develop immunity to some diseases you’ve already
had.
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Section 21.2 Defenses Against Disease
The Immune Response
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Section 21.2 Defenses Against Disease
The Lymphatic System
• The lymphatic system (lim FAT ik) is a network of
vessels that collects fluid from your tissues and
returns it to the bloodstream.
• The fluid flowing through the lymphatic system is
called lymph (limf).
• The lymphatic vessels have hundreds of small
stations, called lymph nodes.
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Section 21.2 Defenses Against Disease
The Lymphatic System
Your lymphatic system is a
complex network of vessels
and nodes.
Lymph
nodes
Lymph
vessel
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Section 21.2 Defenses Against Disease
Passive and Active Immunity
Passive Immunity
• Immunity acquired by receiving antibodies from a
source other than one’s own immune system is
called passive immunity.
• This type of immunity is temporary, not lifelong.
• It occurs naturally in babies, who receive antibodies
from their mothers before birth.
• Passive immunity can be artificially acquired.
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Section 21.2 Defenses Against Disease
Passive and Active Immunity
Active Immunity
• Active immunity results from either having a disease
or from receiving a vaccine.
• Injections, which cause you to become immune to a
disease, are called immunizations
(im yuh nih ZAY shunz), or vaccinations.
• The substance that is injected is called a
vaccine (vak SEEN).
• Vaccines contain small amounts of dead or modified
pathogens or their toxins.
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Section 21.2 Defenses Against Disease
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Section 21.2 Defenses Against Disease
Vocabulary
mucous
membrane
inflammation
phagocyte
immune system
lymphocyte
The protective lining that covers any opening
into the body.
The body’s general response to all kinds
of injury.
A type of white blood cell that engulfs and
destroys pathogens.
The body’s most sophisticated defense
against pathogens.
A type of white blood cell that carries out
functions of the immune system.
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Section 21.2 Defenses Against Disease
Vocabulary
immunity
The body’s ability to destroy a pathogen that it
has previously encountered before the pathogen
is able to cause disease.
T cell
A type of lymphocyte that helps the immune
system destroy pathogens.
B cell
A lymphocyte that produces antibodies.
antibody
A protein that attaches to the surface of
pathogens or to the toxins produced by
pathogens, keeping the pathogen or toxin from
harming the body.
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Section 21.2 Defenses Against Disease
Vocabulary
lymphatic
system
immunization
vaccine
A network of vessels that collects fluid from
body tissues and returns it to the bloodstream;
contains much of the immune system.
An injection that causes the body to become
immune to an infectious disease; also called
a vaccination.
A substance containing small amounts of dead
or modified pathogens or their toxins that is
injected during an immunization.
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