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Microbiology - Nonspecific Body Defense

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Study GuideMicrobiology–Nonspecific Body Defense1. Nonspecific Mechanisms of DefenseThe human body has severalnonspecific defense mechanismsthat protect against many differentmicroorganisms. These defenses are callednonspecificbecause they act againstall types ofpathogens, not just one particular organism.Their main goals are:•Toprevent microorganisms from enteringthe body•Todestroy pathogensif they reach deeper tissues1.1Mechanical Barriers–The First Line of DefenseMechanical barriers are part of the body’snormal structure and function. They act as thefirst lineof defenseat portals of entry.SkinTheskinis one of the strongest mechanical barriers.•The outer layer consists of tightly packed cells•These cells are filled withkeratin, an insoluble protective protein•This thick layer iswaterproofandresistant to infection•When intact, skin is usuallyimpenetrable to pathogensMucous MembranesMucous membranes line the:•Respiratory tract•Digestive tract•Urinary tract

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Study GuideAlthough these membranes aremoist and permeable, they are protected by fluids such as:•Tears•Saliva•MucusThese fluids wash away microorganisms and irritants.Additional protective actions include:•Nasal hairs, which trap particles•Ciliain the respiratory tract, which sweep trapped particles away•Coughing, which forcefully removes irritantsChemical DefensesThe body also produceschemical substancesthat help destroy microorganisms.Examples include:•Lysozymein tears and salivaoBreaks down peptidoglycan inGram-positive bacterial cell walls•Lactic acidin the vaginaoCreates an acidic environment that inhibits microbial growth•Hydrochloric acidin the stomachoA powerful barrier that kills many swallowed microorganisms•Sperminein semenoInhibits bacterial growth in the male urogenital tractGenetic BarriersAn individual’sgenetic makeupcan influence susceptibility to disease.•Humans can become infected withHIVbecause human T-lymphocytes have the requiredreceptor sites•Animals such as dogs and catscannot get HIVbecause they lack these receptors•Conversely, humans do not getcanine distemperbecause they lack the necessary viralreceptor sitesThus, genetic factors can act as anatural barrier to infection.

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Study GuideInflammationInflammationis a nonspecific response toany type of tissue injury, including infection.It is characterized by four classic signs:•Redness•Heat•Swelling•PainInflammation helps the body by:•Bringing immune cells to the injured area•Activating repair mechanisms•Encouragingphagocytesto destroy invading microorganismsChemical Control of InflammationInflammation is regulated by:•Nervous system signals•Cytokines, which are chemical messengers released by tissue and blood cellsLoss of fluid from blood vessels causesedema(localized swelling).In some infections, dead cells, bacteria, and phagocytes collect aspus.FeverFeveris another nonspecific defense response.•It is triggered by substances calledpyrogens•Pyrogens act on thehypothalamusin the brain•The hypothalamus raises the body’s temperatureAlthough very high fever can be harmful, moderate fever is beneficial because:•It slows the growth oftemperature-sensitive microorganisms•It increases cellular metabolism•It enhances immune responses andphagocytosis
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Document Details

University
Texas A&M University
Course
Microbiology
Subject
Anatomy and Physiology

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