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Figure 12.5 Lymphoid organs.

Tonsils (inpharyngeal region)

Thymus (in thorax;most active duringyouth)

Spleen (curvesaround left side ofstomach)

Peyer’s patches (in intestine)

Appendix

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Figure 12.3 Distribution of lymphatic vessels and lymph nodes.

Regional

lymph nodes:

Cervical

nodes

Axillary

nodes

Inguinal

nodes

KEY:

Drained by the right lymphatic duct

Drained by the thoracic duct

Lymphatics

Cisterna chyli (receives

lymph drainage from

digestive organs)

Spleen

Aorta

Thoracic duct

Thoracic duct

entry into left

subclavian vein

Internal jugular vein

Entrance of right

lymphatic duct into right

subclavian vein

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Figure 12.1 Relationship of lymphatic vessels to blood vessels.

Venous

system

Arterial

system

Heart

Lymph duct

Lymph trunk

Lymph node

Lymphatic

system

Lymphatic

collecting

vessels,

with valves

Lymph

capillaryTissue fluid

(becomes

lymph)

Blood

capillaries

Loose connective

tissue around

capillaries

What type of vessel from the cardiovascular system do lymphatic vessels follow?

Why do you think it follows those vessels and not the others?

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Figure 12.2 Distribution and special structural features of lymphatic capillaries.

Tissue fluid

Tissue cell

Lymphatic capillary

Bloodcapillaries

Arteriole Venule

(a) (b)

Endothelialcell

Filaments anchored to connective tissue

Flaplike minivalve

Fibroblast in looseconnective tissue

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Figure 12.4 Structure of a lymph node.

Germinal center in follicle Capsule

Subcapsular

sinus

Trabecula

Efferent lymphaticvessels

Hilum

Medullary sinus

Medullary cord

Follicle

Cortex

Afferent lymphaticvessels

Afferent lymphaticvessels

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Figure 12.6 An overview of the body’s defenses.

Video: Introduction to how the immune system works

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Table 12.1 Summary of Innate (Nonspecific) Body Defenses (1 of 3)

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Table 12.1 Summary of Innate (Nonspecific) Body Defenses (2 of 3)

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Table 12.1 Summary of Innate (Nonspecific) Body Defenses (3 of 3)

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Figure 12.8 Phagocyte mobilization.

Positivechemotaxis

Inflammatorychemicals diffusingfrom the inflamedsite act as chemotactic agents

Neutrophils

Enter blood from bone marrow

and roll along the vessel wallDiapedesis

Capillary wallEndotheliumBasement membrane

1 2

3

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Figure 12.7 Flowchart of inflammatory events.

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Figure 12.9a Phagocytosis by a macrophage.

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Figure 12.9b Phagocytosis by a macrophage.

Phagosome(phagocyticvesicle)

Lysosome

Acidhydrolaseenzymes

(b) Events of phagocytosis

Phagocyte adheres to pathogens.

Phagocyte engulfs the particles, forming a phagosome.

Lysosome fuses with the phagocytic vesicle, forming a phagolysosome.

Lysosomal enzymes digest the pathogensor debris, leaving a residual body.

Exocytosis of the vesicleremovesindigestible and residual material.

2

1

4

3

5

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Figure 12.10 Activation of complement, resulting in lysis of a target cell.

Membrane attackcomplex forming

Activated complement proteins attach to pathogen’s

membrane in step-by-step sequence, forming a

membrane attack complex (a MAC attack).

MAC pores in themembrane lead tofluid flows that cause cell lysis.

Antibodiesattached topathogen’smembrane

Pore

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Figure 12.11 Lymphocyte differentiation and activation.

Red bone marrow: site of lymphocyte origin

Primary lymphoid organs: site ofdevelopment of immunocompetence asB or T cells

Secondary lymphoid organs: site ofantigen encounter, and activation tobecome effector and memory B or T cells

Lymphocytes destined to become T cellsmigrate (in blood) to the thymus and develop immunocompetence there. B cells develop immunocompetence in red bone marrow.

Immunocompetent but still naive lymphocytes leave the thymus and bone marrow. They “seed” the lymph nodes, spleen, and other lymphoid tissues, where they encounter their antigen and become activated.

Antigen-activated (mature) immunocompetent lymphocytes (effector cells and memory cells) circulate continuously in the bloodstream and lymph and throughout the lymphoid organs of the body.

Lymph nodes,spleen, and otherlymphoid tissues

Bone marrowThymus

Immature (naive)lymphocytes

Red

bone marrow

1

2

3

KEY:

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Figure 12.12 Clonal selection of a B cell.

Primary Response(initial encounterwith antigen)

Antigen

Antigen bindingto a receptor on aspecific B cell(B cells withnon-complementaryreceptors remaininactive)

Proliferation toform a clone

MemoryB cell

Subsequent challengeby same antigen resultsin more rapid response

Activated Bcells

Plasmacells

Secretedantibodymolecules

Secondary Response (can be years later)

Clone of cellsidentical toancestral cells

MemoryB cells

Plasmacells

Secretedantibodymolecules

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Figure 12.15a Basic antibody structure.

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Figure 12.15b Basic antibody structure.

Antigen-bindingsites

Lightchain

Heavychain

Disulfidebonds

(b)

C C

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Table 12.2 Immunoglobulin Classes (1 of 2)

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Table 12.2 Immunoglobulin Classes (2 of 2)

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Figure 12.16 Mechanisms of antibody action.

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Figure 12.13 Primary and secondary humoral responses to an antigen.

Primaryresponse

Secondaryresponse

Rela

tive a

nti

bo

dy c

on

cen

trati

on

in b

loo

d p

lasm

a

Time (weeks)Antigeninjected

Antigeninjected

0 1 2 3 4 5 6

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Figure 12.14 Types of acquired immunity.

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Figure 12.19 A summary of the adaptive immune responses.

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Figure 12.17 T cell activation and interactions with other cells of the immune response.

Antigen “Presented”antigen

T cell antigenreceptor

Cytotoxic(killer)T cell

Cell-mediatedimmunity(attack oninfected cells)

Humoralimmunity(secretion ofantibodies byplasma cells)

B cell

Cytokines

HelperT cell

Self-

proteinAntigenprocessing

Dendritic cell

Cytokines

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Table 12.3 Functions of Cells and Molecules Involved in Immunity (1 of 4)

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Table 12.3 Functions of Cells and Molecules Involved in Immunity (2 of 4)

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Table 12.3 Functions of Cells and Molecules Involved in Immunity (3 of 4)

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Table 12.3 Functions of Cells and Molecules Involved in Immunity (4 of 4)

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Sensitization stage

Antigen (allergen)invades body.

Plasma cells producelarge amounts of classIgE antibodies againstallergen.

IgE antibodies attachto mast cells in bodytissues (and to circulatingbasophils).

Mast cell with fixed IgEantibodies

Granules containinghistamine

IgE

Subsequent (secondary)responses

More of same allergeninvades body.

Allergen binding to IgE on mast cells triggersrelease of histamine (and other chemicals).

Antigen

Mast cell granules release contents after antigen bindswith IgE antibodies

Histamine

Histamine causes blood vessels to dilate and become leaky,which promotes edema; stimulates release of large amounts ofmucus; and causes smooth muscles to contract.

Outpouring of fluid from capillaries

Release of mucus

Constriction of bronchioles

1

2

3

4

5

6

Figure 12.20 Mechanism of an immediate (acute) hypersensitivity response.