Body Defenses and Immunity

The Lymphatic System

Consists of two semi-independent parts

Lymphatic vessels

Lymphoid tissues and organs

Lymphatic system functionsTransports escaped fluids back to the blood

Plays essential roles in body defence and resistance to disease

Lymphatic Characteristics

Lymph - excess tissue fluid carried by lymphatic vessels

Properties of lymphatic vessels

One way system toward the heart

No pump

Lymph moves toward the heart

Lymph

Harmful materials that enter lymph vessels

Bacteria

Viruses

Cancer cells

Cell debris

Lymph Nodes Filter lymph before it is returned to the blood

Defense cells within lymph nodesMacrophages—engulf and destroy foreign substances

Lymphocytes—provide immune response to antigens

Lymphatic Vessels

Lymph capillariesWalls overlap to form flap-like mini-valves

Fluid leaks into lymph capillaries

Capillaries are anchored to connective tissue by filaments

Higher pressure on the inside closes mini-valves

Fluid is forced along the vessel

Types of Defenses

Innate (nonspecific defenses)

Function the same way regardless of the pathogen type

Adaptive (specific) defenses

Immunity: targets certain pathogens

Based on body’s ability to distinguish “self” from “non-self”

Antigen – molecule that elicits an immune response

Nonspecific Defenses

Species resistance

Mechanical barriers

Chemical barriers

Fever

Inflammation

Phagocytosis

Inflammation

Redness from blood vessel dilation

Swelling from increased permeability of capillaries

Heat from increased blood flow

Pain

Phagocytosis

“Cell eating”

Performed by neutrophils and macrophages that form from monocytes

Development of Cells of Immunity

Fetal bone marrow forms lymphocytesLymphocytes differentiate:

In thymus T cellsIn marrow B cells

T cells can form B cellsT and B cells circulate in bloodstream and are concentrated in lymph nodes and spleen

T Cell Types

Helper T cellsStimulate B cells to produce antibodies specific to an antigen

Memory T cellsProduced upon initial exposure to antigen but do not act until future exposure to the same antigen

Cytotoxic T cellsDestroy cancerous or virally-infected cells using perforinOnce activated, proliferate to increase clones

Primary vs. Secondary Immune Responses

Primary Immune Response

Occurs with first exposure to an antigenProduction and release of antibodies continues for several weeksAfter primary response, memory T and B cells are produced

Secondary Immune Response

Occurs with future exposures to antigen

Faster response time

Primary Immune Response

• Macrophages engulf invaders and present them to helper T cells in the nearest lymph node.

Cell-Mediated Immunity

• T cells attach to foreign cells and:

a. Secrete toxins that kill target cells.

b. Secrete growth-inhibiting factors that prevent target cell growth.

c. Secrete interferon that inhibits proliferation of viruses and tumor cells.

Antibody-Mediated Immunity

• Helper T cells activate B cells.

• B cells produce clones (plasma cells and memory B cells) and antibodies.

• Antibodies destroy antigen.

Adaptive Immune Responses

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Antibody Actions

Directly attach to antigen and destroy it

Label the antigen for destruction by macrophages

Stimulate localized changes that help prevent the spread of antigens

Secondary Immune Response

Same process as primary immune response with some exceptions:

Faster response time

Memory B cells produce clones quickly

Allergic Reactions

An immune attack against a non-harmful substanceMay be caused by inherited tendency to overproduce IgE antibodies in response to certain antigensIgE triggers the release of histamine allergy symptomsIf reaction is severe anaphylactic shock

Types of Immunity

Naturally acquired active immunity

Develops after a primary immune response

Artificially acquired active immunity

Vaccine stimulates a primary immune response without causing symptoms

Artificially acquired passive immunity

Injection of antibodies; susceptibility may persist

Naturally acquired passive immunity

Antibodies passed to fetus from mother; persists 6 months to one year after birth

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Autoimmunity

When the immune system attacks “self”

Examples of autoimmune diseases

Multiple sclerosis - white matter of brain and spinal cord are destroyed

Type I diabetes mellitus - destroys pancreatic beta cells that produce insulin

Rheumatoid arthritis - destroys joints