(1) List as many non-specific barriers to infection as possible. How does each f
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(1) List as many non-specific barriers to infection as possible. How does each function? (2) What are the names of the granulocytes? From what lineage are they derived? (3) What cell types carry out phagocytosis? When does a monocyte become a macrophage? (4) Describe the five steps of phagocytosis. What is the purpose of each step? How is a microbe digested without destroying the phagocytic cell? (5) What are the signs of inflammation? What physiological changes are responsible for these signs? What purposes does inflammation serve? (6) What are the steps of phagocyte migration? What are the specific functions of neutrophils and macrophages at the site of infection? How do these functions help integrate the function of the innate/non-specific immune system with that of the specific/acquired immune system? (7) How can a bacterial or viral infection produce a fever? What is the purpose of fever? (8) What conditions cause cells to produce interferons? What happens when interferons bind to their receptors on neighboring cells? Against what types of pathogens are interferons most effective? (9) Explain in general the classical pathway of complement activation. What kinds of bacteria and viruses are most susceptible to destruction by the Membrane Attack Complex (MAC)? How does the classical complement path differ from the alternate and lectin-based complement pathways? (10) Name four ways in which complement activation can lead to destruction of a microbe. (11) Why are nonspecific responses so important in preventing infection? (12) What is the difference between non-specific host defense/innate immunity and acquired immunity? Give an example of each. (13) What is the structure of a lymph node, and how does that contribute to functioning in the immune system? (14) What are the types of lymphocytes? How do T cells differ from B cells? How do TH and TC cells differ from one another? What is a natural killer cell? (15) Draw an antibody molecule (IgG). Label heavy and light chains. Label constant and variable regions and the Fab and Fc fragments. Which region is responsible for antigen binding? Which region is responsible for interacting with the rest of the immune system? (16) What are the 5 classes of antibodies and what are their primary functions? (17) What events occur during a humoral immune response? What is the difference between T-independent and T-dependent B cell responses? What types of antigens are best managed by each response and why? (18) Graph the course of an immune response. How does the primary response differ from the secondary (memory) response? (19) Describe five ways in which antibody production may lead to destruction, clearance, or neutralization of a harmful microbe or toxin. (20) Draw the molecular junction between a T cell and a cell displaying a target antigen. What molecule presents antigen to the T cell receptor? Are there differences between T helper cell and T killer cell binding and recognition? What happens to a T cell after it has been activated? (21) What kinds of cells are most efficient at presenting ingested microbial antigens to T cells? What are these cells called? How are those antigens presented? (22) What are the four principles that govern the acquired immune system? How do these govern the acquired immune response in terms of antigen recognition, yet not destroying the host? (23) What is the difference between Th1 and Th2 responses? (24) Explain an entire immune response to a pathogen, from the time that pathogen first gets past barrier defenses to the point that a specific immune response is generated. Follow the course for humoral and cellular responses. Be sure to include every molecule and interaction in as much detail as possible.Explanation / Answer
nonspecific defenses, innate defenses, are inherited mechanisms that protect the body from many kinds of pathogens. Nonspecific defenses, which typically act very rapidly, include BARRERS; such as the skin, molecules that are toxic to invaders. In addition most animals and plants have nonspecific barriers.
Host defenses that protect against infection include natural barriers (eg, skin, mucous membranes), nonspecific immune responses (eg, phagocytic cells [neutrophils, macrophages] and their products), and specific immune responses (eg, antibodies, lymphocytes).
Natural Barriers
Skin: The skin usually bars invading microorganisms unless it is physically disrupted (eg, by injury, IV catheter, or surgical incision). Exceptions include human papillomavirus, which can invade normal skin, causing warts, and some parasites (eg, Schistosoma mansoni, Strongyloides stercoralis).
Mucous membranes: Many mucous membranes are bathed in secretions that have antimicrobial properties (eg, cervical mucus, prostatic fluid, and tears containing lysozyme, which splits the muramic acid linkage in bacterial cell walls, especially in gram-positive organisms). Local secretions also contain immunoglobulins, principally IgG and secretory IgA, which prevent microorganisms from attaching to host cells.
Respiratory tract: The respiratory tract has upper airway filters. If invading organisms reach the tracheobronchial tree, the mucociliary epithelium transports them away from the lung. Coughing also helps remove organisms. If the organisms reach the alveoli, alveolar macrophages and tissue histiocytes engulf them. However, these defenses can be overcome by large numbers of organisms or by compromised effectiveness resulting from air pollutants (eg, cigarette smoke) or interference with protective mechanisms (eg, endotracheal intubation, tracheostomy).
GI tract: GI tract barriers include the acid pH of the stomach and the antibacterial activity of pancreatic enzymes, bile, and intestinal secretions. Peristalsis and the normal loss of epithelial cells remove microorganisms. If peristalsis is slowed (eg, because of drugs such as belladonna or opium alkaloids), this removal is delayed and prolongs some infections, such as symptomatic shigellosis. Compromised GI defense mechanisms may predispose patients to particular infections (eg, achlorhydria predisposes to salmonellosis). Normal bowel flora can inhibit pathogens; alteration of this flora with antibiotics can allow overgrowth of inherently pathogenic microorganisms (eg, Salmonella typhimurium) or superinfection with ordinarily commensal organisms (eg, Candida albicans).
GU tract: GU tract barriers include the length of the urethra (20 cm) in men, the acid pH of the vagina in women, and the hypertonic state of the kidney medulla. The kidneys also produce and excrete large amounts of Tamm-Horsfall mucoprotein, which binds certain bacteria, facilitating their harmless excretion.
Nonspecific Immune Responses
Cytokines (including IL-1, IL-6, tumor necrosis factor, interferon-) are produced principally by macrophages and activated lymphocytes and mediate an acute-phase response that develops regardless of the inciting microorganism (see also Biology of the Immune System: Cytokines). The response involves fever and increased production of neutrophils by the bone marrow. Endothelial cells also produce large amounts of IL-8, which attracts neutrophils.
The inflammatory response directs immune system components to injury or infection sites and is manifested by increased blood supply and vascular permeability, which allows chemotactic peptides, neutrophils, and mononuclear cells to leave the intravascular compartment. Microbial spread is limited by engulfment of microorganisms by phagocytes (eg, neutrophils, macrophages). Phagocytes are drawn to microbes via chemotaxis and engulf them, releasing phagocytic lysosomal contents that help destroy microbes. Oxidative products such as hydrogen peroxide are generated by the phagocytes and kill ingested microbes. When quantitative or qualitative defects in neutrophils result in infection, the infection is usually prolonged and recurrent and responds slowly to antimicrobial drugs. Staphylococci, gram-negative organisms, and fungi are the pathogens usually responsible.
Specific Immune Responses
After infection, the host can produce a variety of antibodies, complex glycoproteins known as immunoglobulins that bind to specific microbial antigenic targets. Antibodies can help eradicate the infecting organism by attracting the host's WBCs and activating the complement system. The complement system (see Biology of the Immune System: Complement System) destroys cell walls, usually through the classic pathway. Complement can also be activated on the surface of some microorganisms via the alternative pathway. Antibodies can also promote the deposition of substances known as opsonins (eg, the complement protein C3b) on the surface of microorganisms, which helps promote phagocytosis. Opsonization is important for eradication of encapsulated organisms such as pneumococci and meningococci.
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The human body has a multitude of natural barriers in place to prevent infection and disease. These barriers can be both external and internal. The external barrier is the largest organ of your body, your skin. The internal barriers are your immune system, your stomach acid, the blood-brain barrier and the placental barrier.
The human skin blocks the entrance of disease-causing microbes into the body. The skin helps regulate the body's temperature, which in turn keeps the organ systems functioning at an optimal level. The skin also plays a role in water retention; it prevents water from leaving your body, thus preventing dehydration. The average person's skin covers 1.5 to 2 square meters. Skin is comprised of three primary layers the epidermis, the dermis and the hypodermis.
A human's immunity is comprised of a complex system of biological structures and processes. The immune system is designed to distinguish external pathogens from your own tissue and neutralize their harmful effects. The immune system includes white blood cells, non-specific defense mechanisms, and humoral and chemical barriers.
Inflammation is a response conducted by your immune system; Inflammation is a complex biological response to tissue damage. Inflammation not only destroys pathogens, but it also initiates the tissue-healing process.
Gastric acid is a substance excreted by cells in the wall of your stomach. This acid not only helps digestion but also neutralizes many microbes that are ingested with the products you eat and drink. In the absence of gastric acid during certain diseases there is almost always a multitude of infections present in your digestive tract.
The blood-brain barrier is caused by a system of endothelial cells located around the capillaries that enter the central nervous system (CNS). These cells prevent large molecules from circulating in the CNS; they also prevent the entrance of most bacteria. It is because of the blood-brain barrier that bacterial infections of the brain are extremely rare.
The placenta is an organ that connects an unborn child to its mother. The placenta weighs about 500 grams (approximately two pounds). The placenta provides the unborn child with nutrients from the mother and also denies entry to microbes that would cause infection in the unborn child.
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