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LEARN STEP #2 Make the connections to key topics.

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UNIT 3 Essential Nursing Interventions

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CHAPTER 20 Promoting Asepsis & Preventing Infection

pathogens they have encountered before. This is why people who recover from an infectious disease like mea- sles never get the disease again, even if they are repeat- edly exposed to the virus. The cells involved in specific immunity are the lymphocytes, WBCs produced from stem cells in the red bone marrow. There are two main types of lymphocytes: T cells and B cells. Key Point: Both B cells T cells form in the bone marrow. B cells remain in the bone marrow until they are fully mature. T cells go to the thymus to mature. Both are activated against pathogens within the lymphatic system (lymph nodes, spleen, tonsils) to protect and preserve health and pre- vent infection. The receptors on the surface of these two types of lymphocytes allow them to recognize invaders. Cellular Immunity The cellular (cell-mediated) immune response acts directly to destroy infection-causing pathogens (i.e., viruses, fungi, protozoans, cancers) without using antibodies but, rather, by activating phagocytes and T cells (Fig. 20-2). 1. The immune process starts when the body is exposed to a particular pathogen. Infecting microbes in the body invade cells and signal for more microbes to take over. 2. Antigens are proteins on the outer surface of patho- gens that evoke an immune response. 3. Along comes WBC phagocytes that engulf and swal- low the pathogen. 4. After the pathogen is destroyed, the phagocyte now displays pieces of itself on the antigens of the destroyed pathogen. This is known as an antigen- presenting cell (APC). 5. Now memory T cells bind to the APC to fight similar pathogens in the future. With subsequent infections, memory T cells increase the speed and intensity of the T-cell response to recognize similar intruders. 6. Nearby helper T cells come in and fight against the infecting agent by activating T cells and alerting B cells to get involved. 7. Active T cells multiply to fight the infection by releas- ing proteins and enzymes to destroy the pathogen. These are called cytotoxic (killer) T cells. 8. Suppressor T cells stop the immune response when the infection has been contained (also see Fig. 20-3). Humoral Immunity The humoral immune response (or antibody-mediated response) protects the body by circulating antibodies to fight against pathogens. The body’s defense system acts by producing specialized WBCs (leukocytes) to seek out and destroy invaders (Fig. 20-3). This is how a humoral immune response works to fight against pathogens: ■ A person is exposed to a pathogen. ■ Helper cells in the bone marrow activate proteins, called interleukins, that cause B cells to divide into memory cells and active B cells.

Antigen (pathogen)

Knowledge Check 20-3 ■ Identify and describe the purpose of the body’s three major lines of defense against infection. ■ If a patient’s laboratory work reveals that immunoglobulin M (IgM), but not immunoglobulin G (IgG), is present in the blood, what could you conclude about this infection?

Antigen

Phagocyte

B cell

Antigen

WHAT FACTORS INCREASE HOST SUSCEPTIBILITY?

B cell

Promoting Asepsis & Preventing Infection

T cell

Anything that weakens the body’s defense system makes a person more susceptible to infection. In addi- tion, any factors that increase the person’s exposure to pathogens, such as working at a day care facility or being a nurse, increase the risk for infection. Developmental Stage Young children are vulner- able because their immune systems are immature and they have had limited exposure to pathogens. Children frequently begin to have more infections when they start having contact with people outside their family (e.g., when they attend day care or start school). Acquiring active immunity is a part of the developmental process. Older adults are also susceptible hosts because the immune response declines with aging. Skin, a primary defense, becomes less elastic and more prone to breakdown with aging. Older adults also tend to be less active, tend to have other under- lying illnesses, and their nutrition may be inadequate. Breaks in the First Line of Defense A break in the skin, whether caused by a surgical procedure, injury, skin breakdown, an insect bite, or insertion of an IV device, creates a portal of entry for infectious microorganisms. Illness or Injury A coexisting infection, illness, or injury limits the physical resources available to combat a new pathogen. Tobacco Use ■ Smoking is a major risk factor for pulmonary infec- tions because it interferes with normal respiratory functioning, including the ability to move the chest, cough, sneeze, and have full air exchange. ■ Chemicals in tobacco immobilize cilia; thus, secretions pool in the lower airways, creating a favorable envi- ronment for bacteria to live and replicate. ■ Smoking and vaping adversely affect the immune sys- tem by compromising the antibacterial function of leu- kocytes. As a result, chronic exposure to secondhand smoke increases the risk for respiratory infection, ear and sinus infection, meningitis, and postsurgical and nosocomial infections (Bagaitkar et al., 2008). Substance Abuse ■ Alcohol curbs hunger. As a result, many chronic alco- hol users do not consume an adequate diet, leading to vitamin, mineral, and protein deficiency. Over time,

Helper T cell

APC

Interleukins

Cytotoxic T cell

Helper T cell

Memory T cell

Neutrophil

Promoting Asepsis & Preventing Infection

Memory cell

Helper T cell

FIGURE 20-3 The humoral immune response produces antibodies to destroy antigens.

FIGURE 20-2 The cell-mediated immune response causes white blood cells to attach to antigens.

■ Active B cells produce Y-shaped antibodies that bind to the pathogen’s attachment site (antigen) and interfere with its ability to infect other cells (Box 20-2). This process, called neutralization, does not destroy pathogens; it just makes them ineffective. ■ Antibodies also cause pathogens to clump together (agglutination), reducing their activity and increas- ing the likelihood that the clump will be detected and phagocytized by leukocytes. ■ These antibodies signal leukocytes (macrophages and neutrophils) to come in and engulf the pathogen and break it down. ■ Antibodies also fight infection by triggering inflammatory chemicals to destroy the pathogen. This is called the complement cascade, described earlier. ■ Suppressor cells stop the immune response when the infection is contained.

BOX 20-2 ■ Immunoglobulin (Ig) Classes

Promoting Asepsis & Preventing Infection

■ IgM is the first antibody to appear when an antigen (e.g., pathogen) is encountered. It is also involved in agglutination with incompatible blood types. ■ IgG is the most common immunoglobin in the body. It takes at least 10 days for IgG to be produced in response to an initial infection. IgG is the only immunoglobulin that can cross the placenta to provide temporary immunity to the fetus/infant. ■ IgE is the immunoglobulin primarily responsible for the allergic response. ■ IgA is found in mucous membranes in the intestines, respiratory and urinary tracts, saliva, tears, and breast milk. IgA provides additional immune protection by secreting around the body openings. ■ IgD forms on the surface of B cells and traps the potential pathogen to prevent it from replicating and causing disease.

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