chapter 43 the body’s defenses. the nature of disease pathogenic organismspathogenic organisms...
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The Nature of Disease
• Pathogenic OrganismsPathogenic Organisms• Genetic DisordersGenetic Disorders• Toxic ChemicalsToxic Chemicals• Other Environmental FactorsOther Environmental Factors• Physical Damage to OrgansPhysical Damage to Organs• Nutritional DisordersNutritional Disorders
Types of Pathogenic Organisms
• VirusesViruses• BacteriaBacteria• ProtozoanProtozoan• FungiFungi• AnimalAnimal• ParasitesParasites
Mechanisms of Disease by Pathogens
• Utilization of host nutritional Utilization of host nutritional resourcesresources
• Physical damage to host tissuesPhysical damage to host tissues• Production of toxic substancesProduction of toxic substances• Chromosomal and gene damageChromosomal and gene damage• Body cells behave abnormallyBody cells behave abnormally
• Skin acts as barrier to microbes and viruses- sweat has a low pH
• Mucus traps foreign particles• Tears
- Lysozyme has antimicrobial action• Gastric stomach acid
1st Line of Defense
• Phagocytic cells (WBCs)- N L M E B- Natural Killer (NK) Cells: attack virus
infected cells• Inflammatory Response• Antimicrobial proteins
- Lysozyme- Interferon- Antibodies
2nd Line of Defense
Inflammatory Response
Histamine & prostaglandins released
Capillaries dilateClotting begins
Chemotactic factors attract phagocytic cells
Phagocytes consume pathogens & cell debris
Characteristics of Immunity
• Recognition of self versus non-self• Response is specific• Retains a “memory” allowing an
accelerated second response• Can respond to many different
materials• Involves lymphocytes and
antibodies
Types of Immunity
• Active Immunity- Naturally-Acquired Active Immunity- Artificially-Acquired Active Immunity
• Passive Immunity- Naturally-Acquired Passive Immunity- Artificially-Acquired Passive Immunity
• The production of antibodies against a specific disease by the immune system.
• Naturally acquired through disease
• Artificially acquired through vaccination – Vaccines include inactivated toxins, killed
microbes, parts of microbes, and viable but weakened microbes.
• Active immunity is usually permanent
Active Immunity
• A vaccinated person has a secondary response based on memory cells when encountering the specific pathogen.– Routine immunization against infectious
diseases such as measles and whooping cough, and has led to the eradication of smallpox, a viral disease.
– Unfortunately, not all infectious agents are easily managed by vaccination.• HIV vaccine in the works
• Passive Immunity- Protection against disease through antibodies produced by another human being or animal.
• Effective, but temporary
• Ex. Maternal antibodies
• Colostrum.
Passive Immunity
• Passive immunity can be transferred artificially by injecting antibodies from an animal that is already immune to a disease into another animal.– Rabies treatment: injection with antibodies
against rabies virus that are both passive immunizations (the immediate fight) and active immunizations (longer term defense).
Immune System Response to Antigens
Humoral Immunity• Involves antibodies (secreted from B
cells) dissolved in the blood plasma.• Demonstrated as a immune response
using only the blood serum.• Defense against bacteria, bacterial
toxins, & viruses.
Cell-Mediated Immunity• Involves the activities of specific
white blood cells (T cells).• Defense against cancer cells, virus-
infected cells, fungi, animal parasites, & foreign cells from transplants.
Immune System Response to Antigens
B Cells
• Mature in bone marrow• Involved in humoral immunity• Once activated by antigen,
proliferate into two clones of cells: plasma cells that secrete antibodies and memory cells that may be converted into plasma cells at a later time
Humoral Immune Response
time (days)
antib
ody
conc
entr
atio
n
first exposure to antigen A
primary response: concentration of anti-A antibodysecond exposure
to antigen A
Humoral Immune Response
time (days)
antib
ody
conc
entr
atio
n
secondary response: concentration of anti-A antibody
second exposure to antigen A
first exposure to antigen B
Humoral Immune Response
time (days)
antib
ody
conc
entr
atio
n
primary response: concentration of anti-B antibody
first exposure to antigen B
• Antibodies constitute a group of globular serum proteins called immunoglobins (Igs).– A typical antibody molecule has two identical
antigen-binding sites specific for the epitope that provokes its production.
Mechanisms on Antibody Action
• Precipitation of soluble antigens• Agglutination of foreign cells• Neutralization• Enhanced phagocytosis• Complement activation leading to cell lysis• Stimulates inflammation
• The binding of antibodies to antigens to form antigen-antibody complexes is the basis of several antigen disposal mechanisms.
Immunoglobin ClassesImmunoglobin Classes
IgM• 1st response to antigen• Effective in agglutination• Can’t cross placenta
IgG• Most common form• Crosses blood vessels• Crosses placenta
(passive immunity to fetus)
IgA• Secreted from mucus
membranes• Prevents attachment of
bacteria to epithelial surface• In colostrum
IgD• B cell activation• Can’t cross placenta
IgE• Histamine
reactions and allergies
T Cells
• Mature in thymus• Involved in cell-mediated immunity• Activated when another cell
presents antigen to them• Several types of T cells: cytoxic T
cells, helper T cells, suppressor T cells, and memory T cells
• There are two main types of T cells, and each responds to one class of MHC molecule.– Cytotoxic T cells (TC) have antigen receptors
that bind to protein fragments displayed by the body’s class I MHC molecules.
– Helper T cells (TH) have receptors that bind to peptides displayed by the body’s class II MHC molecules.
T Cells
–T-independent antigens• T cells activated by binding to certain
antigens
• No memory cells generated
• Weaker response than t-dependent
–T-dependent antigens• Most antigens require co-stimulation to
evoke a B-cell response
• Antibody production stimulated with help from TH
• Most antigens are t-dependent
• T-dependent antigens- can trigger a humoral immune response by B cells only with the participation of helper T cells.
• Malfunctions of the immune system can produce effects ranging from the minor inconvenience of some allergies to the serious and often fatal consequences of certain autoimmune and immunodeficiency diseases.
Abnormal immune function can lead to disease
Autoimmune Disease• Rheumatoid arthritis• Type I Diabetes• MS• Lupis• Crohn’s disease• Grave’s disease
ABO Blood Types
PhenotypePhenotype GenotypeGenotypeOO i ii iAA I I A A I I AA or I or I A A
iiBB I I B B I I BB or I or I B B
iiABAB I I A A I I BB
Type A
ABO Blood TypesABO Blood Types
Produces Produces anti-B anti-B antibodiesantibodies
b
b
b
b
b
b
b
b
Type B
ABO Blood TypesABO Blood Types
Produces Produces anti-A anti-A antibodiesantibodies
a
a
a
a
a
a a
a
aa
Type O
ABO Blood TypesABO Blood Types
Produces Produces both anti-A both anti-A and anti-B and anti-B antibodiesantibodies
a
a
a
a
a
aa
a
aa
b
b
b
b
b
b
b
b
Rh Factor and
Pregnancy
Rh+ mother w/Rh- baby– no problemRh- mother w/Rh+ baby– problemRh- mother w/Rh- father– no problemRh- mother w/Rh- baby-- no problem
RhoGAM used @ 28 weeks
Allergy (Immune Hypersensitivity)
• Hypersensitive response to certain environmental allergens
• Food, pollen, pet dander, asthma, bee sting
• Anaphylactic shock - epinephrine
AIDS
Acquired Immunodeficiency Syndrome
HIV (virus) attacks T-cells
Weakens or eliminates immune system
Susceptible to many fatal diseases
ProblemsProblems
• Transmission of HIV requires the transfer of body fluids containing infected cells, such as semen or blood, from person to person.– Unprotected sex – Nonsterile needles – HIV transmission among heterosexuals is
rapidly increasing as a result of unprotected sex with infected partners.
– HIV in Africa and Asia- primarily by heterosexual sex
AIDS• In 1983, a retrovirus, now called human
immunodeficiency virus (HIV), had been identified as the causative agent of AIDS.
• With the AIDS mortality close to 100%, HIV is the most lethal pathogen ever encountered.– Molecular studies reveal that the virus probably
evolved from another HIV-like virus in chimpanzees in central Africa and appeared in humans sometimes between 1915 and 1940.• These first rare cases of infection and AIDS went
unrecognized.