The Immune System

39.2 DEFENSE AGAINST INFECTIOUS DISEASES

First line of defense: Barriers



Nonspecific defense: includes the skin and mucous membranes  Skin ○ serves as a physical barrier against pathogens ○ Releases sweat that contains lysozyme ( a chemical that is toxic to bacteria)  Mucous membranes line the respiratory & digestive

tracts

○ Secrete mucus, a sticky substance that traps pathogens ○ Cilia sweep mucus & pathogens up to the pharynx where

they are swallowed

 Stomach ○ Stomach acids destroy swallowed pathogens

Second line of defense: nonspecific immunity

 Inflammatory

response: a series of events that suppress infection & speed recovery.

White Blood Cells  Basophils

are found in the blood. They release histimine at an infection site.  Eosinophilsrelease enzymes to fight pathogens. They have limited phagocytic activity

White Blood Cells 

Phagocytes are white blood cells that ingest & destroy pathogens and foreign matter Neutrophils are the most abundant type of

phagocytes. They circulate through blood vessels and squeeze through capillary vessels to infection sites Monocytesare small immature macrophages. They circulate in the blood. When they reach an infected area they leave blood & mature into macrophages. Macrophages are phagocytes found in body tissues (lysosomal enzymes inside macrophages digest the ingested particles)

Temperature response Temperature above 37oC is called a fever.  Some pathogens trigger fever  Chemical released by macrophages trigger a fever  A moderate fever may slow bacterial & viral growth & promote WBC activity  High fevers are dangerous because extreme heat can destroy important cellular proteins 

Proteins  About

20 proteins make up the complement system. They circulate in the blood & become active when they encounter a pathogen Interferons are proteins released by cells

infected with viruses Interferons diffuse to uninfected neighboring cells, which then produce antiviral proteins that prevent the virus from multiplying.

Overview of the Body’s defense

Specific defenses: Immune System 

The immune system is made up of the:  Bone marrow: place where

lymphocytes are made  Thymus: gland above the heart, helps produce T cells  lymph nodes: small mass of tissue that filters pathogens from lymph and exposes them to lymphocytes  spleen: stores healthy blood cells  tonsils: provide protection against bacteria & pathogens that enter nose & mouth  Lymphocytes: B cells & T cells

Immune Response  Immune

Response: reaction of the body against an antigen  Antigen: any foreign substance that the immune system can react with Pathogens or parts of pathogens Bacterial toxins Insect venom Pollen Any molecule that is not part of an individual’s

body

Antibody immunity

Cellular immunity

Immune response animation

 http://highered.mcgraw-

hill.com/sites/0072507470/student_view0 /chapter22/animation__the_immune_resp onse.html

Primary vs. Secondary immune response 

The secondary immune response (the second time you’re exposed to an antigen) is faster and more powerful than the primary immune response

Passive vs. Active Immunity



Passive acquired immunity: develops as a result of acquiring antibodies that are generated in another host Natural: during pregnancy from mom to baby

through placenta, or through mom’s milk Artificial: antibody injections 

Active acquired immunity: obtained when a person is exposed to antigens Vaccine: a substance consisting of a weakened

or dead, or incomplete pathogen which produces and immune response

HIV & AIDS 



AIDS: acquired immunodeficiency syndrome, where the immune system loses the ability to fight off pathogens and cancers AIDS is caused by the human immunodeficiency virus, HIV  HIV binds and replicates inside macrophages but doesn’t

destroy them  HIV attaches & replicates inside T helper cells (virus destroys the T helper cells) It eventually kills enough T helper cells to cripple the immune system  Infected individuals can have the HIV virus for up to 10 years without showing signs of AIDS  A person is diagnosed with AIDS when the number of T helper cells drops dramatically where the T helper cells no longer stimulate B cells and cytotoxic T cells to fight invaders.

Transmission of HIV 

HIV is transmitted by the transfer of bodily fluids containing HIV or HIV-infected cells. Sexual contact with an infected person Use of syringes and hypodermic needles that

have been contaminated with blood containing HIV Infected mother to her baby before or during birth or through breast-feeding Blood transfusion (low rate) HIV is NOT transmitted through casual contact, through the air, in water, on toilet seats or through insect bites