Key Concepts:
Vocabulary: immune system, inflammatory response, phagocytes, antigens, immunity, lymphocyte, antibody, vaccine
Physical and Chemical Barriers
Main Idea: Physical and chemical barriers make up your body’s first line of defense against pathogens.
You wear a coat or sweater to stay warm, a hat to keep the sun offyour head and face, and a helmet during.many sports activities. Your coat, sweater, hat, and helmet are all barriers that protect your body, but have you ever stopped to think about how your body deals with invasion from microscopic pathogens? Your body has its own built-in barriers to handle these tiny invaders.
There are two kinds of barriers that help protect you: physical and chemical. Physical barriers, such as the skin, block pathogens from invading your body. Chemical barriers, such as the enzymes in tears, destroy those invaders. See Figure 23.5 for more examples of physical and chemical barriers that defend you against pathogens.
The Immune System
Main Idea: Your body’s immune system is your best ally in the fight against communicable diseases.
Although your body’s physical and chemical barriers stop many pathogens before they can cause infection or disease’ pathogens can-and , do-sneak past these defenses. That’s when your immune system, a network ofcells, tissues, organs, and chemicals that fights off pathogens, goes to work. The immune system fights pathogens using two major strategies: the inflammatory response and specific defenses.
Skin is like a personal coat of armor, stopping most pathogens in their tracks as they try to enter the body. Cilia are small hairs that line parts of your respiratory system. Cilia sweep mucus and pathogens to the throat, where they can be swallowed or coughed out. Gastric juice in the stomach destroys many pathogens that enter your body through the nose or mouth. With the pathogens killed and tissue damage under control, the body begins to repair the tissue.
The Inflammatory Response
Have you ever gotten a splinter or a cut? If so, you probably remember that the affected area became red and swollen. These are symptoms ofthe inflammatory response, a reaction to tissue damage caused by injury or infection. This response prevents further injury to the tissue and stops the invading pathogens. Your immune system knows a foreign object such as a wood splinter might have pathogens on it. It also knows that a cut could allow pathogens to get into your body. That’s why it triggers the inflammatory response.
The inflammatory response, which works against all types
of pathogens, includes the following actions.
1. In response to tissue damage and invading microorganisms blood vessels near the injury expand. This allows more blood to flow to the area and begin fighting the invading pathogens.
2. Fluid and cells from the bloodstream cause swelling and pain because of pressure on the nerve endings.
3. Phagocytes, white blood cells that attack invading pathogens, surround the pathogens and destroy them with special chemicals. Pus, a mass of dead white blood cells and damaged tissue, may build up at the site of inflammation as a response to bacteria.
4. With the pathogens killed and tissue damage under control, the body begins to repair the tissue.
Specific Defenses
Although the inflammatory response kills many pathogens, some may survive. So, in addition to the inflammatory response, the immune system triggers specific defenses in reaction to certain pathogens. This process is called the immune response. When the immune system recognizes a particular pathogen, it activates specific defenses in an attempt to prevent this type of infection from occurring again.
Figure 23.6 describes the immune response. During this process, your immune system reacts quickly to antigens, sub- stances that can trigger an immune response. Antigens are found toxins and on the surfaces of pathogens. Macrophages, a type of phagocyte, make antigens recognizable to white blood cells.
This enables the white blood cells to destroy the pathogens. The result of this type of immune response is known as immunity, the state of being protected against a particular disease.
Lymphocytes
The lymphocyte, a specialized white blood cell that coor- dinates and performs many functions of specific immunity, plays an important role in the immune response. There are two types of lymphocytes: T cells and B cells.
T Cells This type of lymphocyte has a variety of functions:
Helper T cells trigger the production of B cells and killer T cells.
Killer T cells attack and destroy infected body cells. These cells don’t attack the pathogens, only the infected cells.
Suppressor T cells coordinate the actions of other T cells. They suppress, or “turn off,” helper T cells when the infection has been cleared.
B Cells
These lymphocytes have just one job: producing antibodies. An antibody is a protein that acts agains a specific antigen. Each B cell is programmed to make one type of antibody that is specific to a certain pathogen. The different purposes of antibodies include
attaching to antigens to mark them for destruction.
destroying invading pathogens.
Immune System Memory
Your immune system also “remembers” the antigens it has dealt with in the past. When antigens activate certain T cells and B cells, the cells become memory lymphocytes. These special memory cells circulate in your bloodstream and through the lymphatic system, shown in Figure 23.7. When memory cells recognize a former invader, the immune system sends antibodies and killer T cells to stop the invasion. For example, if you’ve had measles or been vaccinated against it, your immune system remembers and will attack the antigens for the measles virus.
Your immune system’s memory not only identifies invading pathogens. It also helps you develop immunity from certain diseases. There are two types of immunity: active and passive.
Active Immunity
This type of immunity develops from natural or artificial processes. Your body develops naturally acquired active immunity when it is exposed to antigens from invading pathogens. Artificially acquired active immunity is developed from a vaccine, a preparation of dead or weakened pathogens that are introduced into the body to stimulate an immune response.
Vaccines cause your immune system to produce disease- fighting antibodies without causing the disease itself. Today, more than 20 serious human diseases can be prevented by vaccination. For some diseases, you need to be vaccinated only once in your life. For other diseases, such.as measles, tetanus, and influenza, you may need to be vaccinated at regular intervals.
Passive Immunity You acquire passive immunity when your body receives antibodies from another person or an animal. This type ofimmunity is temporary, usually lasting only a few weeks or months. Like active immunity, passive immunity can be either natural or artificial.
Natural passive immunity occurs when antibodies pass from mother to child during pregnancy or while nursing. Artificial passive immunity happens when you receive an injection prepared with antibodies that are produced by an animal or a human immune to the disease immune response.
Prevention Strategies
Main Idea: Strategies for preventing the spread of disease include practicing healthful behaviors, tracking diseases, and getting vaccinations.
The immune system is a powerful fighter against infection, and you can keep it tuned up and in good working order by eating a nutritious, well-balanced diet and getting regular physical actIVIty. In addition, you can take preventive measures to avoid disease and stay healthy. These include frequent hand washing, handling food properly, avoiding insect bites, and abstaining from sexual contact.
Tracking Reportable Disease
Community, national, and global efforts also play a crucial role in fighting communicable diseases. Agencies such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) keep a constant watch on the spread of diseases around the world. By tracking infections such as hepatitis, influenza, and yellow fever, they can often predict where the diseases might strike next. This information helps countries prepare and develop their own prevention strategies.
Vaccinations
In the past, smallpox killed hundreds of millions of people. Today, thanks to the smallpox vaccine, the disease has been essentially wiped out. Scientists and health care workers are always trying to stay one step ahead of commu- nicable diseases and develop new vaccines. Vaccines fall into four categories:
Live-virus vaccines are made from pathogens grown in laboratories. This process removes most of the pathogens’ disease-causing characteristics. The pathogens are weak, but they can still stimulate the immune system to produce antibodies. The vaccine for measles, mumps, and rubella (MMR) and the vaccine for chicken pox are produced this way.
Killed-virus vaccines use dead pathogens. Even though the pathogens are no longer active, they still stimulate an immune response. Flu shots, the Salk vaccine for polio, and the vaccines for hepatitis A, rabies, cholera, and plague are all killed-virus vaccines.
Toxoids are inactivated toxins from pathogens. They are used to stimulate the production of antibodies. Tetanus and diphtheria immunizations use toxoids.
New and second-generation viruses are on the cutting edge ofdisease-fighting technology. One example is the vaccine for hepatitis B, which is made from genetically altered yeast cells.
Immunization for All
When you receive a vaccine, you are not only keeping yourself healthy, but you are also helping to protect everyone around you.Vaccination reduces the number of people who are at risk for a communicable disease. That’s why it’s important to keep your immunizations up-to-date.
Emerging Infections
Main Idea: Some diseases are becoming more dangerous and widespread.
Vaccines and modern technology have saved millions of lives, but communicable diseases continue to be the top cause of deaths worldwide. Health experts label some communicable diseases as emerging infections, communicable diseases whose occurrence in humans has increased within the past two decades or threatens to increase in the near future.
Scientists now believe that some diseases once thought to be noncommunicable may, in fact, be caused by infectious pathogens. Such diseases include Alzheimer’s, diabetes, and coronary artery disease. Many factors are involved in the development and spread of these diseases.
How Diseases Affect the World
Main Idea: Diseases can spread with amazing speed.
The world’s countries are connected through trade and travel. These connections make it easy for infectious diseases to spread. Sometimes a disease becomes a pandemic-a global outbreak ofan infectious disease. An outbreak of avian flu or E. coli in a small area of the globe can quickly spread and threaten the health of entire countries, even continents.
Medical treatment and prevention requires constant research to find the causes and the cures for emerging diseases. The U.S. government has launched programs that will educate the public about flu pandemics. Health agencies plan for pandemics and develop rapid-response strategies to reduce their impact.
The Impact of Travel
The mobility of people in our globalized world contributes to the spread of disease. For example, an American tourist can pick up an infection in another country, return home, and spread it to his family, friends, and coworkers.
© 2020-2025. All Rights Reserved.