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BIO120H1 (305)
Chapter 1

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University of Toronto St. George
Bebhinn Treanor

Chapter 1  Immunology-study of the physiological mechanisms that humans and other animals use to defend their bodies from invasion by other organisms  Infectious disease are caused by microorganisms, which have the advantage of reproducing and evolving much more rapidly than their human hosts  In response, the human body invests heavily in cells dedicated to defense=immune system  All humans suffer from infectious diseases because the immune system takes time to build up its strongest response to an invading microorganism, time during which the invader can multiply and cause disease  To provide immunity that will provide protection from the disease in the future, the immune system must do battle with the microorganism o Ppl at greatest risk during first infection o Without modern medicine, a lot of child mortality o Ex: indigenous americans killed by euro diseases, HIV, AIDS  The greatest triumph of immunology has been vaccination or immunization o Procedure where severe disease is prevented by prior exposure to the infectious agent in a form that cant cause disease o Provides opportunity for immune system to gain experience needed to make a protective response with little risk to health o First used against smallpox in Asia, Lady Montagu introduced it into western Europe o Jenner, a doctor in England, showed how inoculation with cowpox virus offered protection against smallpox with less risk then earlier methods, called it vaccination…credited with the invention o Ppl used to use trial and error method to produce vaccines..not used as much now since all the easily won vaccines have been made o New knowledge is being used to find better ways to manipulate immune system to prevent the unwanted immune responses that cause allergies, autoimmune disease, and rejection of organ transplants  First line of defense is innate immunity, which includes physical and chemical barriers to infection, and reponses that are ready and waiting to halt infections before they can barely start o Most infections are stopped by this mechanism, but when it fails, the more flexible and forceful defenses of the adaptive immune response are brought into play…when successful, it clears the infection and provides long-lasting immunity that prevents its recurrence Numerous commensal microorganisms inhabit healthy human bodies  More than 500 microbial species live in a health adult human gut and contribute about 2 pounds to the bodys weigh, called commensal species (eat at the same table)  The community of microbial species that inhabits a particular niche in the human body-skin, mouth, gut, vagina…called flora…ex: the gut flora  Cant be studied properly because they require special conditions  Commensal organisms enhance human nutrition by processing digested food and making vitamins. Protect against disease by preventing colonization of disease causing microorganisms. Ex: E-Coli secrete colicins that incapacitate other bacteria preventing from colonizing the gut o When person takes antibiotics most of the normal gut flora is killed along with the disease causing bacteria. o New microorganisms recolonize…ex: opportunistic disease causing bacteria like (C. difficile) cause further disease and death…produces toxin causing diarrhea or pseudomembranous colitis  Pathogen-any organism with potential to cause disease  Opportunistic pathogen-colonize body with no effect until bodys defense is weak or if microbe gets into wrong place  4 types of pathogen o bacteria o virus o fungi o parasites  rapid death of host not in a microbes interest because this destroys both its home and source of food o therefore, often evolve towards an accommodation with their hosts o complementary fashion, humans have evolved genetic resistance to common disease causing organisms as well as acquiring lifetime immunity to endemic diseases=most ppl are exposed to in childhood, abundant in population (chicken pox, measles, malaria)  influenza-severe symptoms but overcome by immune system o new pathogens like ebola cause 60-75% death  skin is bodys first defense o impenetrable barrier of epithelium protected by keratinized cells o epithelium-layers of cell lining outer surface and inner cavities of body o until the adoption of antiseptic procedures in 19 century, surgery very risky because infections…soldiers in battle die moreso because of infections then enemy attack  Mucosal surface/mucosa- epithelium lining resp (sinus, trachea, lung), GIT (Oral cavity, eso, stomach, intestine), Urogenital tract (kidney, bladder, vagina). Tissues specialized for communication with their enviro and more vulnerable to microbial invasion o thick fluid layer contains glycoproteins, proteoglycans, enzymes to protect epithelial cells from damage and limit infection o in respiratory tract-mucus removed by epithelial cells with beating cilia and replenished by goblet cells  all epithelial surfaces secrete antimicrobial substances o secrete antimicrobial peptides called defensins that kill bacteria, fungi, virus by perturbing their membrane o sebum secreted by sebaceous glands associated with hair follicles…contains FA and lactic acid…inhibits bacterial growth on skins surface o tears and saliva contain lysozyme-kills bacteria by degrading cell wall o also destroyed by acidic enviro of stomach, vagina, skin  Surface epithelia provide mechanical, chemical and microbiological barriers  skin-perspiration, sebum, flora  GIT-saliva, fluid, mucus, acidity, enzymes, flora  Respiratory-cilia, lysozyme, flora  Urogenital-sperm, mucus, acidity in vagina, flora  Eyes-tears, lysozyme, flora  innate immune response-acts quickly o 1) recognition that pathogen is present. Involves soluble proteins and cell surface receptors that bind to either pathogen or human cells and serum proteins…become altered o 2) recruitment of effector mechanisms that kill and eliminate it. Effector mechanisms are provided by effector cells-engulf bacteria, kill virus infected cells or attack protozoan parasites. Also complement helps effector cells by marking pathogens with molecular flags but also attack pathogen  Pathogen recognition o Bacterial cell surface induces cleavage and activation of complement o One complement fragment covalently bonds to bacterium, other attracts an effector cell o The complement receptor on effector cell binds to the complement fragment on the bacterium o Effector cell engulfs bacterium (phago), kills it, breaks it down  cells and proteins in damaged tissue sense presence of bacteria and the cells send out cytokines that interact with other cells to trigger innate immune response o induces inflammation in infected tissue o inflammation-calor (heat), dolor (red), rubor (swell)…symtoms due to immune response  cytokines induce local dilation of blood capillaries=increase blood flow=skin warms/red  vasodilation introduces gaps btw cells of endothelium (layer of specialized epithelium lining interior of blood vessels) o makes endothelium permeable and increases leakage of blood plasma into CT o expansion of local fluid volume causes edema (swelling)-puts pressure on nerve endings=pain  cytokines also change the adhesive properties of the vascular endothelium, WBC attach it to and move from the blood into inflamed tissue  inflammatory cell-WBC that are usually present in inflamed tissues and release substances that contribute to inflammation  some infections outrun the innate immune response, which then works to slows the spread of infection while calling up lymphocytes to increase the power and focus of the immune response o this is the adaptive immune response because it adapts to the infecting pathogen o very specialized  effector mechanisms same as adaptive immune response except the cell surface receptors used my lymphocytes recognize the pathogens.  In innate immunity=receptors are different and not specific  Adaptive immunity=receptors are all of same molecular type and highly specific o Infection occurs, only lymphocytes with receptors that recognize pathogen are selected and proliferate (clonal selection) o Lymphocyte differentiate to produce a lot of effector cells specific for the pathogen (clonal expansion)  Some lymphocytes selected during an adaptive immune response persist in the body and provide long term immunological memory of pathogen o Therefore, stronger and faster adaptive immune response o Adaptive immunity provide my immunological memory also called acquired immunity or protective immunity  Pathogens like measles give immunity for decades but influenza is short lived o Because influenza changes yearly to escape immunity  Primary immune response-first time adaptive immune response is made  Secondary immune response-after the first time  Purpose of vaccination is to induce immune memory to a pathogen so subsequent infection with pathogen elicits strong fast acting adaptive response  Adaptive immunity is better understood than innate immunity  Cells of immune system are mos
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