Immune system.pdf

Immune system Pathogens Bacteria: Viruses: rely on living human cells for extremely small infectious agents. Structurally simple, consisting solely of a their energy supply, and in the small piece of genetic material (either RNA or DNA) surrounded by a protein process they damage or kill the coat. R...

Immune system Pathogens Bacteria: Viruses: rely on living human cells for extremely small infectious agents. Structurally simple, consisting solely of a their energy supply, and in the small piece of genetic material (either RNA or DNA) surrounded by a protein process they damage or kill the coat. Regardless of the method of entry à presence of the viral genetic human cells. generally treated material à cell produces virion à instead of its own metabolic activities. with antibiotics— Antibiotics generally don’t work à cure a viral infection à stop an infected chemotherapeutic agents that host cell from producing more viruses or prevent virions from entering. inhibit or abolish the growth Prions: disease in British cattle that in the animals’ brains and spinal cord. as well. it is defined as: misfolded form of normal brain cell protein that can trigger the misfolding of nearby normal proteins. They enter nerve cells à misfolding becomes self propagating. Lymphatic system closely associated with the cardiovascular system. The The lymphatic system begins as a network of small, lymphatic system performs 3 functions: blind- ended lymphatic capillaries in the vicinity of the cell and blood capillaries. • maintain the volume of blood. The fluid in the lymphatic capillaries is lymph, a milky • It transports fats and fat-soluble vitamins body fluid that contains, proteins, fats, and the absorbed from the digestive system to the occasional bacterium/virus. Lymphatic capillaries merge cardiovascular system. = lymphatic vessels. • Defends the body against infection. Lymph nodes cleanse the lymph: The spleen cleanses blood: Located at intervals along the are small largest lymphatic organ. soft, fist- sized mass located in the upperorgans called lymph nodes. The lymphatic left abdominal cavity. covered with a dense capsule of connective system consists of a network of lymphatic tissue interspersed with smooth muscle cells. Inside the organ à2 types of tissue, red pulp and white pulp. vessels throughout the body, lymph nodes, the thymus gland, tonsils, adenoids, and the spleen 2 functions: controls the quality of circulating RBC by spleen. Lymph nodes remove removing the old and damaged ones & it helps fight infection. microorganisms, cellular debris, and red pulp àcontains macrophages àscavenge and break down abnormal cells from the lymph before microorganisms + old and damaged RBC and platelets à store for returning it to the cardiovascular system. in case of blood loss or a fall in blood pressure (extra oxygenThere are hundreds of lymph nodes, carrying capacity). white pulp à contains primarily lymphocytes àsearch foreign clustered in: digestive tract, neck, armpits, and groin. pathogens. Thymus gland hormones cause T lymphocytes to mature: thymus gland is located in the lower neck, behind the sternum and just above the heart. Encased in connective tissue, the gland contains lymphocytes and epithelial cells. The thymus gland secretes two hormones, thymosin and thymopoietin, that cause certain lymphocytes called T lymphocytes (T cells) to mature and take an active role in specific defenses. first line of defense Skin: Tears, saliva, and earwax: Tears à lubricating the eyes and washing away 4 key attributes that make an effective barrier: (1) its structure, (2) constantly being replaced, (3) its particles + lysozyme. Saliva à lubricates the delicate tissues inside the mouth acidic pH (4) the production of an antibiotic by sweat glands. àdo not dry out and crack. It also rinses Mucus: microorganisms safely from the mouth into the stomach thick, gel-like material secreted by cells at various àkilled by stomach acid. Earwax à traps small particles and microorganisms. surfaces of the body, including the lining of the digestive tract and the branching airways of the respiratory system. Microorganisms à contact mucus à mired and cannot gain access to the cells beneath. Digestive and vaginal acids: Vomiting, urination, and defecation: Undiluted digestive acid is strong enough to kill nearly Vomiting à toxic or infected stomach contents. all pathogens only Helicobacter pylori can survive à Urination à lightly acidic+ constant flushing. ulcer. Vaginal secretions are slightly acidic, too, though Defecation à remove microorganisms from the not nearly as acidic as stomach secretions. digestive tract. Nonspecific defenses: the second line of defense do not target specific pathogens. Instead, they appear in response to all types of health challenges. The complement system, or complement, comprises at least 20 plasma proteins that circulate in the blood and complement, or assist, other defense mechanisms. Activated complement proteins link together à protein complexes à create large holes through the bacterial cell wall àWater and salts leak into the bacterium through the holes à the bacterium swells and bursts (lyses). Other activated complement proteins bind to bacterial cell membranes àmarking them for destruction by phagocytes à others stimulate mast cells à histamine or serve as chemical attractants à draw additional phagocytes to the infection. Phagocytes engulf foreign cells: Inflammation: redness, warmth, swelling, and pain: phagocytes are white blood cells that destroy Injury à inflammatory response, or inflammation. foreign cells through the process of Inflammation has four outward signs: redness, warmth, phagocytosis. swelling, and pain. A phagocyte first captures a bacterium with its Function: release of chemicals from damaged cells à cytoplasmic extensions à draws the bacterium stimulate WBC basophil and mast cells, which are connective in à engulfing it (endocytosis) àenclosing it in tissue cells specialized to release histamine àpromotes a membrane-bound vesicle àfuses with vasodilation of neighboring small blood vessels àactivate lysosomes àenzymes in the lysosomes dissolve complement proteins, which diffuse out of the leaky capillaries the bacterial membranes àcompleteàphagocyte and begin destroying bacteria. jettisons the bacterial wastes by exocytosis. - most white blood cells (phagocytes) are too large to Neutrophils are the first white blood cells to cross capillary walls. However histamine dilates blood respond to infection. They digest and destroy vessels à endothelial cells in vessel walls pull slightly bacteria and some fungi in the blood and tissue apart, and the vessels become more permeable. This fluids. allows additional phagocytes to squeeze through. When invaders are too big to be engulfed and Vasodilation brings more blood into the injured area, digested by phagocytosis, other white blood cells making it red and warm. The rising temperature called eosinophils take action. increases phagocyte activity. Natural killer cells target tumors and virus-infected Interferons interfere with viral reproduction: cells: Cells that become infected by viruses secrete a group Natural killer (NK) cells are a group of white blood cells of proteins called interferons. (lymphocytes) that destroy tumor cells and cells infected by viruses. Specific defense mechanisms: the third line of defense The activities of the immune system are The immune system targets antigens: collectively called the immune antigen any substance that mobilizes the immune system and provokes response. an immune response (generally large protein or polysaccharide targets specific enemies à specific molecules). defense mechanisms. Each antigen àimmnue system produce specific antibodies to attack The immune response has three and inactivate the antigen. important characteristics: All antigens are located only on the outer surface of a cell or virus. - recognizes and targets specific viruses (or viral DNA/RNA) à inside a living human cell à immune pathogens or foreign substances. system cannot detect. - It has a “memory,” à store - human cells also have surface proteins that can act as antigens information from past exposures under the right circumstances. à respond more quickly to later - Your cells have a unique set of proteins on their surfaces that invasions by the same pathogen. your immune system uses to recognize that thosecells belong to - It protects the entire body; the you. These self markers are known as major histocompatibility resulting immunity is not limited complex (MHC) proteins. to the site of infection. 1 à 8 cytotoxic , 2 à 4 helper. Lymphocytes are B cells: antibody-mediated immunity: central to specific B lymphocytes mature à bone marrow à develop unique surface receptors (with the same defenses: structure as an antibody) that allow them to recognize specific antigens à they travel in the 2 types of these bloodstream to the lymph nodes, spleen, and tonsils à remain inactive à encounter a WBC: foreign cell with that particular antigen àbind to the antigen àactivates the B cell to grow B lymphocytes +multiply rapidly àproducing more B cells exactly like the = clones. mature à bone most of the cells of the clone are called plasma cells because they begin to secrete their marrow à antibodies into the lymph fluid and ultimately into the blood plasma. A typical plasma cell antibody-mediated can make antibody molecules at a staggering rate—about 2,000 molecules per second. A immunity. B cells plasma cell maintains this frantic pace for a few days and then dies, but its antibodies produce antibodies. continue to circulate in blood and lymph. T lymphocytes Some clone cells become memory cells, long- lived cells that remain inactive until that same mature à thymus antigen reappears in the body at some future date. gland à cellUpon exposure, these memory cells quickly become plasma cells and start to secrete mediated antibodies. Memory cells are the basis for long-term immunity. immunity, which antibodies encounter matching antigens à bind = antigen- antibody complex. depends on the - Some antibodies inactivate pathogens by causing the cells to agglutinate (clump actions of several together), preventing them from entering human cells and causing disease. More types of T cells. commonly, antigen- antibody complex marks the antigen à destruction either by phagocytes or by activated complement proteins. The five classes of antibodies IgG (75% of immunoglobulins): most common class. IgM (5–10%): first to be released during immune Found in blood, lymph, intestines, and tissue fluid, responses. Found in blood and lymph, they activate the activate the complement system and neutralize many complement system and cause foreign cells to toxins. only antibodies that cross the placenta during agglutinate. ABO blood cell antibodies belong to this pregnancy and pass on the mother’s acquired class. immunities to the fetus. IgA (15%): enter areas of the body covered by mucous IgD (less than 1%): IgD antibodies are in blood, membranes, such as the digestive, reproductive, and lymph, and B cells. function is not clear, but they may respiratory tracts. There they neutralize infectious play a role in activating B cells. pathogens. They are also present in a mother’s milk and are transmitted to the infant during breast- feeding. IgE (approximately 0.1%): rarest of the immunoglobulins, IgE antibodies are in B cells, mast cells, and basophils. They activate the inflammatory response by triggering the release of histamine. They are behind allergic responses. An antibody’s structure enables it to bind to a specific antigen All antibodies share the same basic structure, represented by an IgG antibody. Each antibody has 4 linked polypeptide chains arranged in a Y shape. The 2 larger chains are called “heavy” chains, and the two smaller ones are called “light” chains. Each of the four chains has a constant region that forms the trunk and two branches and a variable region that represents the antigen-binding site. Because it has a unique amino acid sequence. The constant regions are similar for all antibodies in one class, although they differ from those of other classes. IgM class consist of five Y-shaped molecules linked together, with 10 binding sites. T cells: cell-mediated immunity two sets of surface proteins, CD4 or CD8. These proteins determine what type of T cell they will become. Active immunization: an effective weapon against pathogens The process of activating the body’s immune system in advance is called active immunization. This involves administering an antigen-containing preparation called a vaccine. Passive immunization can help against existing or anticipated infections To fight an existing or even Passive immunization advantage: anticipated infection, a person can - somewhat effective against an existing infection. be given antibodies prepared in - confers at least some short-term immunity. advance from a human or animal - fetus and newborn Passive immunization occurs naturally across the donor with immunity to that placenta and through breast-feeding. illness. Usually this takes the - used effectively against certain common viral infections, including form of a gamma globulin shot those that cause hepatitis B and measles. (serum containing primarily IgG Disadvantage: antibodies). The procedure is - protection is not as long-lasting as active immunization. à because the called passive immunization. à administered antibodies disappear from the circulation quickly. the patient is given the antibodies - can’t confer long-term immunity against a second exposure, because that his/her own immune system the person’s own B cells aren’t activated and so memory cells for the might produce if there were pathogen do not develop. enough time.