395_CHAP_40.PDF - Pearson Education



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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. Allergies occur when antigens enter the body and bind to mast cells. Mast cells are immune cells found throughout the body. 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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