Chapter_18_Lesson_2_-_Textbook (1).pdf

Keeping Pathogens Out MAIN IDEA​ ​Your body has five major barriers that defend against pathogens​. Pathogens are everywhere. They are on almost all of the surfaces you touch. They are in the air you breathe. So, why aren’t you sick all of the time? Your body has natural barriers between you and pa...

Keeping Pathogens Out MAIN IDEA​ ​Your body has five major barriers that defend against pathogens​. Pathogens are everywhere. They are on almost all of the surfaces you touch. They are in the air you breathe. So, why aren’t you sick all of the time? Your body has natural barriers between you and pathogens. They work to keep pathogens out of your body. These barriers are your body’s first line of defense. The five major barriers are skin, tears, saliva, mucous (MYOO-kuhs) membranes, and stomach acid. Your skin is your body’s largest organ. It is a barrier or wall around the inner organs. The skin produces salty sweat. Most pathogens don’t like salt. The skin also has one-way pores. Sweat can get out, but pathogens can’t get in. Body fluids such as tears and saliva form another barrier. Tears and saliva contain chemicals that kill certain organisms. Mucous membranes are another barrier. They line the insides of your mouth, throat, nose, and eyes. They are coated with a sticky fluid that traps and destroys pathogens. Stomach acid, another barrier, kills the germs that make it past the saliva and mucous membranes in your mouth. Even with all of these barriers, pathogens sometimes find their way into your body. They might get in through a cut or scrape. If pathogens enter the body, you might have an infection​.​ Your body is well-equipped to handle the infection. Infection can trigger a fever in the body. The increase in body temperature caused by the fever makes it difficult for pathogens to live. READING CHECK Identify​ What are five barriers your body has against pathogens? Nonspecific Immune Response MAIN IDEA​ ​Your immune system responds when pathogens get past the five major barriers of protection​. Sometimes your body’s barriers can’t keep out all of the pathogens. For example, when you get a splinter, it breaks the skin. The pathogens that are on the splinter enter your system through the broken skin. When this happens, your immune system responds to the invaders. The response is called a nonspecific immune response. It’s called nonspecific because your body reacts the same no matter what foreign matter enters the body. The splinter or other foreign object will cause the skin around it to become red and sore and swollen. The nonspecific immune system has responded with inflammation. When the splinter enters your system, the brain tells white blood cells to rush to the area. White blood cells destroy the pathogens. When this happens, circulation to the area slows down. When your body has inflammation or other infection, it produces a protein called interferon (in ter FIR ahn). Interferon stimulates the body’s immune system. This helps to stop pathogens from multiplying. If pathogens do multiply and spread, your body temperature may rise. This will cause a fever. A higher body temperature makes it difficult for pathogens to reproduce and multiply. The fever also signals the body to produce more white blood cells. The white blood cells attack and destroy the pathogens. READING CHECK Explain​ What is your body’s first response to invading pathogens? Specific Immune Response MAIN IDEA​ ​The specific immune response attacks quickly if pathogens get past the nonspecific immune response​. It’s possible that some pathogens will get past the body’s nonspecific immune response. When this happens, the body responds with a specific immune response. This is the immune system’s second response. Each specific response is customized to attack a particular pathogen and its poisons, or toxins. Your immune system recognizes pathogens that have invaded before. Your body battled those pathogens. The particular response cells that did battle stay in your body. So if the same types of pathogens attack again, those response cells go into action. They attack and fight the pathogens very quickly. The second response is faster than the first response. The figure in the Lesson Resources panel provides a complete explanation of the immune system response. The Lymphatic System The lymphatic system is an important part of the body’s defense system. It contains fluid called lymph. The lymph flows into the body’s tissues and blood stream fighting pathogens. The lymphatic system contains lymphocytes (LIM fuh sytes). There are three main types of lymphocytes: B cells, T cells, and NK cells. NK stands for “natural killer.” Natural killer cells attack cancers and viruses. B cells are made in the bone marrow. T cells are made in the thymus. B cells and T cells work together to defeat invading pathogens. T cells are like a military intelligence unit. They identify the invaders. Then they send out a chemical communication or alert to the B cells. The B cells attack and kill the invading pathogen. Macrophages are also found in the lymph. Macrophages surround and destroy foreign substances in the body. Then they remove the foreign material from the lymph. They also remove waste products and harmful organisms. Antigens and Antibodies Antigens and antibodies are both invaders. One tries to introduce infection to the body. The other fights that invasion. Antigens are invaders that force the body to react. Antibodies are proteins that attach to antigens to fight the invaders. The three types of lymphocytes—T cells, B cells, and NK cells—react to antigens. The lymphocytes are activated when the body recognizes a part of a pathogen called an antigen. For example, if bacteria enter your system, lymphocytes will recognize substances on the surface of the bacteria as antigens. Also, blood that is a different type than your will be recognized as an antigen. Your body reacts to antigens by making more B cells and T cells. B cells make antibodies. Antibodies fight a particular type of antigen. Using the example from above, special antibodies will attack the antigens on the bacteria. Different antibodies will attack the antigens on the blood. Some of the new B cells and T cells don’t react to the antigens the first time. They wait to react if the same kind of pathogen enters the body again. These are known as memory B cells and memory T cells. T cells either stimulate the production of B cells or attack pathogens directly. There are two main types of T cells: helper cells and killer cells. Helper cells activate the production of B cells. Killer cells attach to invading pathogens and destroy them. Immunity MAIN IDEA​ ​Your body has different types of immunity​. You have several different types of immunity. You are born with natural immunities. For example, there are germs that affect animals that do not affect you. When your pet gets sick, you probably won’t get sick from your pet. Pathogens such as distemper that might make your pet sick won’t make you sick. The reverse is also true. Pathogens that make you sick probably won’t make your pet sick. Other barriers also provide immunity. Those barriers include tears, mucous membranes, saliva, skin, and stomach acid. These barriers can be penetrated by pathogens. If that happens, your immune system takes over to attack the invading pathogens. Babies are born with natural immunities. The mother’s antibodies pass from her body to the body of her baby. After the baby is born, the mother’s milk provides additional antibodies. These antibodies help the baby’s immune system fight pathogens. After the first few months of life, a baby’s own immune system begins to fight pathogens. Your body builds immunity when it responds to pathogens. It also builds immunity when you get certain diseases. When your body encounters antigens, it makes memory B cells and T cells. These memory cells remember the antigens the next time they invade your body. Then they produce antibodies to fight the antigens. Scientists discovered many years ago that they can help the body develop immunities. They can do this by introducing a vaccine into the body. Vaccines help the immune system make antibodies for certain diseases. Diseases vaccines have been developed for include: polio, measles, and chicken pox. Vaccinations such as those for hepatitis B must be given several times over a few months. The vaccine for tetanus must be given throughout your life. It is important to keep vaccinations up to date. The chart in the Lesson Resources panel shows when common vaccinations should be given. Keeping vaccinations up to date helps keeps you healthy. It also helps keep those around you healthy. READING CHECK Explain​ How does your immune system react to a vaccination?