Download Chap 40 summ B Inf Disease

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Chapter 40
# Title
The Immune System and Disease
Summary
40–1 Infectious Disease
A disease is any change, other than an injury, that disrupts normal
body functions. Some diseases are produced by agents, such as
bacteria, viruses, and fungi. Others are caused by materials in
the environment, such as cigarette smoke. Still others, such as
hemophilia, are inherited.
Before the 1800s, scientists did not know that microorganisms
caused infectious diseases. Disease-causing microorganisms are
called pathogens. The idea that infectious diseases are caused by
pathogens was introduced by Louis Pasteur and Robert Koch. This
idea is called the germ theory of disease. Koch also developed a
series of rules called Koch’s postulates. These rules help scientists
identify which organism causes a specific disease.
Viruses, bacteria, protists, worms, and fungi all can be
pathogens. Some pathogens cause disease by destroying cells.
Some release toxins into the body. Other pathogens disrupt body
functions. Infectious diseases can be spread in several ways.
• Some infectious diseases are spread from one person to
another through coughing, sneezing, or physical contact.
Most are spread through indirect contact, such as when
pathogens are carried through the air. These pathogens can
be inhaled, or they can be picked up from surfaces.
• Other infectious diseases are spread through contaminated
water or food.
• Still others are spread by infected animals. Animals that
carry pathogens from person to person are called vectors.
Antibiotics are drugs that kill bacteria without harming the
host’s cells. Antiviral drugs fight some viral diseases. Rest, a
balanced diet, and fluids also help treat disease.
40–2 The Immune System
The function of the immune system is to fight infection through
the production of cells that inactivate foreign substances or cells.
This system makes cells that recognize, attack, destroy, and
“remember” each type of pathogen that enters the body. This
process is called immunity.
The immune system has nonspecific defenses to stop
pathogens from entering the body. These defenses include
physical and chemical barriers.
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• First line of defense. The function of the first line of defense
is to keep pathogens out of the body. This role is carried out
by skin, mucus, sweat, and tears. Your body’s most important nonspecific defense is the skin. It forms a barrier that
few pathogens can get through. Mucus, saliva, and tears trap
pathogens and contain an enzyme that kills bacteria.
• Second line of defense. When pathogens do enter the body,
other nonspecific defenses go to work. The inflammatory
response is a nonspecific defense reaction to tissue damage
caused by injury or infection. Blood vessels near the wound
expand. White blood cells enter the tissues to fight infection.
A fever, or higher than normal body temperature, can slow
pathogen growth. Fever is a chemical response to pathogens.
If a pathogen gets past the nonspecific defenses, specific
defenses go to work. This is called the immune response. There
are two types of immune response.
• In humoral immunity, white blood cells, called B cells, make
antibodies that attack pathogens in the blood. Antibodies
are proteins that recognize and bind to specific antigens.
• In cell-mediated immunity, white blood cells, called
T cells, find and destroy abnormal or infected cells. When
a pathogen is destroyed, memory cells are formed. These
cells respond if the same pathogen enters the body again.
You can acquire immunity without having a disease.
Vaccination is the injection of a weakened or mild form of a
pathogen to cause immunity. Immunity that results from vaccines
is called active immunity. Active immunity appears after exposure
to an antigen. Passive immunity forms when antibodies are introduced into the body. Passive immunity lasts only as long as the
antibodies stay in the body.
40–3 Immune System Disorders
Sometimes, disorders occur in the immune system itself. The
most common disorder is allergies. Mast cells are immune cells
found throughout the body, especially in the linings of the nasal
passages. Allergies occur when antigens bind to mast cells.
The mast cells become activated, and release chemicals called
histamines. Histamines increase the flow of blood and fluids
to the area. This causes allergy symptoms.
When the immune system makes a mistake and attacks the
body’s own cells, an autoimmune disease results. Autoimmune
diseases include Type I diabetes, rheumatoid arthritis, and
multiple sclerosis.
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Immunodeficiency diseases occur when the immune response
breaks down. AIDS is one example of an immunodeficiency
disease. AIDS is caused by HIV (human immunodeficiency virus).
HIV attaches to receptors on helper T cells. Once inside the cells,
HIV copies itself and kills the infected cells. HIV gradually kills off
all the helper T cells. As a result, the immune system can no longer
fight infections.
AIDS can be transmitted from mother to child during pregnancy, childbirth, and breast-feeding. It can also be transmitted
from one person to another through shared needles, contact with
infected blood, and sexual intercourse. The only no-risk behavior
with respect to HIV and AIDS is abstinence.
40– 4 The Environment and Your Health
Anything that increases the chance of disease or injury is a
risk factor. Environmental factors that can affect your health
include air and water quality, poisonous wastes in landfills,
and exposure to solar radiation.
Bioterrorism is a new health threat. Bioterrorism is the
intentional use of biological agents, such as viruses, to disable
or kill people.
Cancer is a life-threatening disease in which cells multiply
uncontrollably and destroy healthy tissue. Cancer may cause a
tumor, a mass of cells that grows out of control. Some tumors are
not cancerous.
All forms of cancer result from harmful mutations. Mutations
may be inherited. Viruses, chemicals, and radiation can also cause
mutations. Sunlight and radon gas are sources of potentially
harmful radiation. Radon gas is found in rocks and can leak into
buildings. Carcinogens are chemicals that cause cancer. Some
carcinogens are produced in nature. Others are made by humans.
For example, tobacco smoke contains carcinogens. Cigarette
smoking is responsible for nearly half of the cancers that occur
in the United States.
You can choose behaviors that help keep your immune system
functioning properly. Some healthful behaviors include:
• eating a healthful diet
• getting plenty of exercise and rest
• abstaining from harmful activities
• having regular checkups
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