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