The Lymphatic System and Body Defenses

The Lymphatic SystemConsists of two semi-independent parts

Lymphatic vesselsLymphoid tissues and organs

Lymphatic system functionsTransports escaped fluids back to the bloodPlays essential roles in body defense and

resistance to disease

Lymphatic CharacteristicsLymph—excess tissue fluid carried by

lymphatic vesselsProperties of lymphatic vessels

One way system toward the heartNo pumpLymph moves toward the heart

Milking action of skeletal muscleRhythmic contraction of smooth muscle in vessel

walls

Relationship of Lymphatic Vessels to Blood Vessels

Figure 12.1

Lymphatic VesselsLymph capillaries

Walls overlap to form flap-like minivalvesFluid leaks into lymph capillariesCapillaries are anchored to connective tissue

by filamentsHigher pressure on the inside closes

minivalvesFluid is forced along the vessel

Lymphatic Vessels

Figure 12.2a

Lymphatic Vessels

Figure 12.2b

Lymphatic VesselsLymphatic collecting vessels

Collect lymph from lymph capillariesCarry lymph to and away from lymph nodesReturn fluid to circulatory veins near the

heartRight lymphatic ductThoracic duct

Figure 12.3

Lymphatic Vessels

LymphHarmful materials that enter lymph vessels

BacteriaVirusesCancer cellsCell debris

Lymph NodesFilter lymph before it is returned to the

bloodDefense cells within lymph nodes

Macrophages—engulf and destroy foreign substances

Lymphocytes—provide immune response to antigens

Lymph Nodes

Figure 12.3

Lymph Node StructureMost are kidney-shaped and less than 1

inch longCortex

Outer partContains follicles—collections of lymphocytes

MedullaInner partContains phagocytic macrophages

Figure 12.4

Lymph Node Structure

Flow of Lymph Through NodesLymph enters the convex side through

afferent lymphatic vesselsLymph flows through a number of sinuses

inside the nodeLymph exits through efferent lymphatic

vesselsFewer efferent than afferent vessels causes

flow to be slowed

Other Lymphoid OrgansSeveral other organs contribute to

lymphatic functionSpleenThymusTonsilsPeyer’s patches

Other Lymphoid Organs

Figure 12.5

SpleenLocated on the left side of the abdomenFilters bloodDestroys worn out blood cellsForms blood cells in the fetusActs as a blood reservoir

Thymus GlandLocated low in the throat, overlying the

heartFunctions at peak levels only during

childhoodProduces hormones (like thymosin) to

program lymphocytes

TonsilsSmall masses of lymphoid tissue around

the pharynxTrap and remove bacteria and other foreign

materialsTonsillitis is caused by congestion with

bacteria

Peyer’s PatchesFound in the wall of the small intestineResemble tonsils in structureCapture and destroy bacteria in the

intestine

Mucosa-Associated Lymphatic Tissue (MALT)Includes

Peyer’s patchesTonsilsOther small accumulations of lymphoid tissue

Acts as a sentinel to protect respiratory and digestive tracts

Body DefensesThe body is constantly in contact with

bacteria, fungi, and virusesThe body has two defense systems for

foreign materialsInnate (nonspecific) defense systemAdaptive (specific) defense system

Immunity—specific resistance to disease

Immune System

Figure 12.6

Body DefensesInnate defense system (nonspecific

defense system)Mechanisms protect against a variety of

invadersResponds immediately to protect body from

foreign materialsAdaptive defense system (specific defense

system)Specific defense is required for each type of

invader

Innate Body DefensesInnate body defenses are mechanical

barriers to pathogens such asBody surface coverings

Intact skinMucous membranes

Specialized human cellsChemicals produced by the body

Innate Body Defenses

Table 12.1 (1 of 2)

Surface Membrane Barriers:First Line of DefenseSkin and mucous membranes

Physical barrier to foreign materialsAlso provide protective secretions

pH of the skin is acidic to inhibit bacterial growthSebum is toxic to bacteriaVaginal secretions are very acidic

Surface Membrane Barriers:First Line of DefenseStomach mucosa

Secretes hydrochloric acidHas protein-digesting enzymes

Saliva and lacrimal fluid contain lysozymes, an enzyme that destroy bacteria

Mucus traps microogranisms in digestive and respiratory pathways

Cells and Chemicals:Second Line of DefensePhagocytesNatural killer cellsInflammatory responseAntimicrobial proteinsFever

Cells and Chemicals:Second Line of DefensePhagocytes

Cells such as neutrophils and macrophagesEngulf foreign material into a vacuoleEnzymes from lysosomes digest the material

Phagocytes

Figure 12.7a

Figure 12.7b

Lysosome

Microbe adheres to phagocyte

Phagocyte engulfs the particle

Phagocytic vesicle isfused with a lysosome

Microbe in fused vesicleis killed and digested bylysosomal enzymes withinthe phagolysosome

Indigestible andresidual materialis removed byexocytosis

Phagocytic vesiclecontaining microbeantigen (phagosome)

Phagolysosome

Lysosomalenzymes

(b)

Internal Innate Defenses: Cells and ChemicalsNatural killer (NK) cells

Can lyse (disintegrate or dissolve) and kill cancer cells

Can destroy virus-infected cells

Cells and Chemicals: Second Line of DefenseInflammatory response

Triggered when body tissues are injuredFour most common indicators of acute

inflammationRednessHeatSwellingPain

Results in a chain of events leading to protection and healing

Figure 12.8

Flowchart of Inflammatory Events

Cells and Chemicals: Second Line of DefenseFunctions of the inflammatory response

Prevents spread of damaging agentsDisposes of cell debris and pathogens

through phagocytosisSets the stage for repair

Cells and Chemicals: Second Line of DefensePhagocytosis

Neutrophils move by diapedesis to clean up damaged tissue and/or pathogens

Monocytes become macrophages and complete disposal of cell debris

Figure 12.9

Enter blood frombone marrow

EndotheliumCapillary wall

Cling tovascular wall

Diapedesis

Positivechemotaxis

Inflammatorychemicals diffusingfrom the inflamedsite act as chemotacticagents

Basal lamina

Neutrophils1

23

4

Cells and Chemicals: Second Line of DefenseAntimicrobial proteins

Attack microorganismsHinder reproduction of microorganisms

Most importantComplement proteinsInterferon

Cells and Chemicals: Second Line of DefenseComplement proteins

A group of at least 20 plasma proteinsActivated when they encounter and attach to

cells (complement fixation)Damage foreign cell surfacesRelease vasodilators and chemotaxis

chemicals, cause opsonization

Cells and Chemicals: Second Line of DefenseInterferon

Proteins secreted by virus-infected cellsBind to healthy cell surfaces to interfere with

the ability of viruses to multiply

Cells and Chemicals: Second Line of DefenseFever

Abnormally high body temperatureHypothalamus heat regulation can be reset

by pyrogens (secreted by white blood cells)High temperatures inhibit the release of iron

and zinc from the liver and spleen needed by bacteria

Fever also increases the speed of tissue repair

Summary of Nonspecific Body Defenses

Table 12.1 (2 of 2)