NORMAL MICROBIOTA & NONSPECIFIC HOST DEFENSES

I.  Normal Microbiota of the Human Body

    A.  Skin
 

    B.  Respiratory tract
 

    C.  Digestive tract
 

    D.  Genitourinary tract
 
 

II.  Introduction to Host Defenses

A. Severity of disease

B. Human body's defense system has two parts


 

III.  Factors Affecting Resistance to Infection

    A.  Nutrition
 

    B.  Age
 

    C.  Genetic factors
 

IV.  First-Line of Defense

    A.  Physical (Anatomical) Barriers

        1.  skin
 

        2.  mucous membranes
 

        3.  nasal passage
 

         4.  lavage (washing)
 

        5.  eye lids
 
 
 

    B.  Chemical Resistance

        1.  skin secretions
 

        2.  stomach acidity
 

        3.  lysozyme
 

        4.  iron binding proteins
 
 

    C.  Competition with normal flora

V.  Second Line of Defense

    A.  Inflammation

        1.  Events of inflammation

               a)  tissue injury

                      chemotaxins

                       bradykinins

                       histamine

                       prostoglandins

                       arachidonic acid
 

             b)  activated endothelial cells
 

            c)  neutrophils slowed down
 

            d)  neutrophils adhere to endothelial adhesion molecules
 

            e)  extravasation
 

             f)  other WBCs may follow
 

            g)  fibrin clot formation
 
 

        2.  Signs of Inflammation

            a)  swelling (edema)
 

            b)  heat
 

            c)  redness
 

            d)  pain
 

            e)  loss of function
 

        3.  Summary

            control/limit infections

            can get out-of-hand

            chronic inflammation
 

     B.  Phagocytosis

        1.  Phagocytic cells

            a)  granulocytes:

                eosinophils: (~3% circulating WBCs)

                basophils: (~0.5%)

                neutrophils: (50-70%)

                leukocytosis

                band forms
 

            b) mononuclear phagocytes

                1. monocytes: (5-10% total WBC in circulation)
 

                2.  fixed macrophage

                    Kupffer, microglial, alveolar, and dendritic cells
 

         2.  Mechanism of phagocytosis

             a)  phagocyte migration
 

            b)  contact

                interaction between pathogen & phagocyte

                opsonins

                surface phagocytosis
 

            c)  ingestion
 

            d)  killing

                phagosome fuses with lysosome

                O2 independant: hydrolyases

                O2 dependant: toxic forms of Oxygen

                reactive nitrogen intermediates

                defensins
 

        3.  Summary

            PMNs arrive first

            phagocytic dysfunction

            nonprofessional phagocytic cells
 

VI. Complement System

    A. Introduction

        precise sequence of enzymatic activation (cascade)

        cascade has an amplification affect
 

    B. Mechanisms of Activation

        Two main pathways of activation

        1. classical
 

        2. alternative

            properidin system
 

        3. consequences

            a)  inflammation
 

            b)  opsonins
 

            c)  cell lysis
 

Last updated January 22, 2009.