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Chapter 14: Host Defenses I- Overview and Nonspecific Defenses
Chapter 14: Host Defenses I- Overview and Nonspecific Defenses
Defense Mechanisms of the Host in Perspective
Figure 14.1
Barriers at the Portal of Entry: A First Line of Defense
Figure 14.2
Figure 14.3
Immunity
•Innate (nonspecific)•Adaptive (specific)
First Line of Defense• Skin and mucous
membranes• Physical factors:
▫ mucus▫ lacrimal apparatus of eye▫ Saliva▫ Hairs ▫ Ciliary escalator▫ Urine
• Chemical factors:▫ sebaceous glands of skin,
sebum▫ fatty acids▫ lysozyme▫ gastric juice
Genetic Differences in Susceptibility•Some hosts are genetically immune to the
diseases of other hosts•Particularly true of viruses
The Second and Third Lines of Defense: An Overview•Immunology: the study of all features of
the body’s second and third lines of defense
•Healthy functioning immune system is responsible for:▫Surveillance of the body▫Recognition of foreign material▫Destruction of entities deemed to be
foreign
Figure 14.4
Self and Nonself
•White blood cells must distinguish self from nonself cells
•Evaluates cells by examining markers on their surfaces
Systems Involved in Immune Defenses•Body compartments
▫Intracellular▫Extracellular▫Lymphatic▫Cerebrospinal▫Circulatory
•Physically separated but have numerous connections
Body Compartments that Participate in Immune Function•Reticuloendothelial system (RES)•Spaces containing extracellular fluid
(ECF)•Bloodstream•Lymphatic system
The Communicating Body Compartments
Figure 14.5
Immune Functions of the Reticuloendothelial System•Provides a passageway within and
between tissues and organs•Coexists with the mononuclear
phagocyte system
Figure 14.6
Origin, Composition, and Functions of the Blood•Circulatory system
▫Circulatory system proper▫Lymphatic system
Figure 14.7
Fundamental Characteristics of Plasma•Hundreds of different chemicals•Main component is water (92%)•Proteins such as albumin and globulins,
immunochemicals, fibrinogen and other clotting factors, hormones, nutrients, dissolved gases, and waste products
A Survey of Blood Cells
•Hematopoesis: production of blood cells•Relatively short life•Primary precursor of new blood cells:
pluripotential stem cells in the marrow▫Red blood cells (erythrocytes)▫White blood cells (leukocytes)▫Platelets (thrombocytes)
•Differentiation
Figure 14.8
Figure 14.9
(a)
(b)
Table 16.1 (1 of 3)
Table 16.1 (2 of 3)
Table 16.1 (3 of 3)
Leukocytes
•Granulocytes•Agranulocytes
Granulocytes
•Neutrophils ▫Phagocytosis
•Eosinophils▫Attack and destroy large eukaryotic
pathogens▫Also involved in inflammation and allergic
reactions•Basophils
▫Parallel eosinophils in many actions
Agranulocytes
•Monocytes•Lymphocytes
Monocytes• Discharged by bone marrow into
bloodstream, live as phagocytes for a few days, then differentiate into macrophages
• Responsible for– Many specific and nonspecific phagocytic and
killing functions– Processing foreign molecules and presenting
them to lymphocytes– Secreting biologically active compounds that
assist, mediate, attract, and inhibit immune cells and reactions
• Dendritic cells
Lymphocytes• Key cells in the third line of defense and the
specific immune response• When stimulated by antigens, transform into
activated cells that neutralize and destroy that foreign substance
• B cells– Humoral immunity: protective molecules
carried in the fluids of the body– Produce specialized plasma cells which
produce antibodies• T cells
– Cell-mediated immunity: T cells modulate immune functions and kill foreign cells
Erythrocyte and Platelet Lines• Erythrocytes
– Develop from stem cells in the bone marrow– Lose their nucleus just prior to entering
circulation– Transport oxygen and carbon dioxide to and from
the tissues• Platelets
– Formed elements in circulating blood– Not whole cells– Function primarily in hemostasis and in releasing
chemicals for blood clotting and inflammation
Components and Functions of the Lymphatic System• Lymphatic system: compartmentalized network
of vessels, cells, and specialized accessory organs
• Transports lymph through a system of vessels and lymph nodes
• Major functions– Provide an auxiliary route for the return of
extracellular fluid to the circulatory system proper– Act as a drain-off system for the inflammatory
response– Render surveillance, recognition, and protection
against foreign materials
Figure 16.5 - Overview
Lymphatic Fluid
•Lymph•Plasmalike liquid formed when certain
blood components move out of blood vessels into the extracellular spaces and diffuse or migrate into the lymphatic capillaries
•Composition parallels that of plasma, but without red blood cells
Lymphatic Vessels
• Along the lines of blood vessels• Similar to thin-walled veins• High numbers in hands, feet, and around
the areola of the breast• Flow of lymph is in one direction only-
from extremities toward the heart• Lymph is moved through the contraction
of skeletal muscles through which the lymphatic ducts wend their way
Lymphoid Organs and Tissues
•Lymph nodes•Thymus•Spleen•Gut-associated lymphoid tissue (GALT)•Tonsils•Loose connective tissue framework that
houses aggregations of lymphocytes
Lymph Nodes
•Small, encapsulated, bean-shaped organs•Usually found in clusters along lymphatic
channels and large blood vessels of the thoracic and abdominal cavities
•Major aggregations: axillary nodes, inguinal nodes, cervical nodes
Spleen
•Similar to a lymph node except it filters blood instead of lymph
•Filters pathogens from the blood
The Thymus: Site of T-Cell Maturation•Thymus originates in the embryo•High rates of activity and growth until
puberty•Shrinks gradually through adulthood•Thymic hormones help thymocytes
develop specificity to be released as mature T cells
Figure 14.11
Miscellaneous Lymphoid Tissue• Bundles of lymphocytes lie at many sites on
or just beneath the mucosa of the gastrointestinal and respiratory tracts
• Tonsils• Breasts of pregnant and lactating women• GALT in the intestinal tract
– Appendix– Lacteals– Peyer’s patches
• Mucosal-associated lymphoid tissue (MALT)• Skin-associated lymphoid tissue (SALT)• Bronchial-associated lymphoid tissue (BALT)
14.2 The Second Line of Defense•Inflammation•Phagocytosis•Interferon•Complement
The Inflammatory Response: A Complex Concert of Reactions to Injury•Reaction to any traumatic event in the
tissues•Classic signs and symptoms
▫Rubor (redness)▫Calor (warmth)▫Tumor (swelling)▫Dolor (pain)
•Fifth symptom has been added: loss of function
Figure 14.12
Chief Functions of Inflammation• Chief functions of inflammation
▫Mobilize and attract immune components to the site of the injury
▫Set in motion mechanisms to repair tissue damage and localize and clear away harmful substances
▫Destroy microbes and block their further invasion
The Stages of Inflammation
Figure 14.13
Process of inflammation
•Vasodilation•Increased permeability of Blood Vessels•Phagocytic migration, diapedesis•Repair system•Fever: role of hypothalamus•Role of interferon
Benefits of Edema and Chemotaxis•Dilutes toxic substances•Fibrin clot can trap microbes and prevent
further spreading•Phagocytosis occurs immediately
Figure 14.14
Fever: An Adjunct to Inflammation•An abnormally elevated body temperature•FUO: fevers of unknown origin•Initiation of fever
▫Pyrogen (product of infectious agent) sets the hypothalamic “thermostat” to a higher setting Muscles increase heat production Peripheral arterioles decrease heat loss
through vasoconstriction
Benefits of Fever
•Inhibits multiplication of temperature-sensitive microorganisms
•Impedes the nutrition of bacteria by reducing the availability of iron
•Increases metabolism and stimulates immune reactions and naturally protective physiological processes
Phagocytosis: Cornerstone of Inflammation and Specific Immunity• General activities of phagocytes
– Survey the tissue compartments and discover microbes, particulate matter, and injured or dead cells
– Ingest and eliminate these materials– Extract immunogenic information (antigens)
from foreign matter• Three main types
– Neutrophils– Monocytes– Macrophages
Figure 14.15
Phagocytosis
•Review formed elements in the blood▫types and functions
•Process of phagocytosis:▫chemotaxis▫adherence▫ingestion▫digestion
Figure 16.7 - Overview
Mechanisms of Phagocytic Recognition, Engulfment, and Killing
Figure 14.17
Figure 16.6
Interferon: Antiviral Cytokines and Immune Stimulants• Interferon (IFN): involved against viruses,
other microbes, in immune regulation and intercommunication
• Three major types– Interferon alpha– Interferon beta– Interferon gamma
• All three classes produced in response to viruses, RNA, immune products, and various antigens
• Bind to cell surfaces and induce changes in genetic expression
• Can inhibit the expression of cancer genes and have tumor suppressor effects
Figure 14.18
Complement: A Versatile Backup System•At least 26 blood proteins that work in
concert to destroy bacteria and certain viruses
•Cascade reaction•Three different pathways that all yield
similar end results▫Classical pathway▫Lectin pathway▫Alternative pathway
Complement System
•Plasma and cell membrane proteins•Functions:
▫lysis of cells▫mediate opsonization▫regulate inflammatory response
•Control: protein system•Overview of complement pathways
Figure 16.9 - Overview (1 of 5)
Complement Cascade
•Initiation•Amplification and cascade•Polymerization•Membrane attack
Classical Pathway
Figure 14.19
Figure 16.12 - Overview
Figure 16.13
Figure 16.11 - Overview
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