DEFENSE AGAINST DISEASE

CORE 6.3

• A pathogen is

• Examples of organisms that cause disease:

• Viruses• Not considered • Needs a

• Causes:

6.3.1 Define pathogen.

http://www.youtube.com/watch?v=ZyAKDIVQzVE

• Bacteria• Prokaryote (lacks nucleus)• Divides by • Causes: (diarrhea), (sore

throat, affects breathing), , , , (muscle

spasms),

http://textbookofbacteriology.net/themicrobialworld/Tetanus.html

• Fungi• Eukaryotes• Causes: , ,

(yeast infection, thrush), (allergic reaction to breathing moldy crop),

http://en.wikipedia.org/wiki/File:FeetFungal.JPG http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002302/

• Protozoa• Animal-like protists• Causes: , (invades intestines,

dysentery, diarrhea), (sleeping sickness)

• Roundworms• Causes: , ,

http://www.cdc.gov/parasites/ascariasis/index.html

Elephantiasis video clip:http://animal.discovery.com/tv-shows/monsters-inside-me/videos/parasite-causes-elephantiasis.htm

• Flatworms• Pork and beef , ,

(bilharzias)

Schistosomiasis “swimmer’s itch” – initial invasionhttp://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002298/

• Antibiotics

• Some work to while others may

• They are naturally occurring substances obtained mainly from fungi or bacteria

• Antibiotics • Viruses are

• Their reproduction relies on

6.3.2 Explain why antibiotics are effective against bacteria but not against viruses.

• Pathogens gain entry to the body using one of the following methods:• – diseases of the

human respiratory system can be transmitted when an infected person coughs or sneezes out droplets containing pathogens, which are breathed in by an uninfected person

• Ex.

• – physical contact with an infected person carries the disease to an uninfected person through natural body openings (many diseases)

• – pathogens in contaminated food or water enter the body through the digestive system

• Ex.

• – allows pathogen to gain entry to body

• Ex.

• – needle may contain pathogens in tiny drop of infected person’s blood left on needle; common mode of transmission in drug addicts

• Ex.

• – only occurs if blood supply is contaminated with a disease such as AIDS

• – sexually transmitted diseases gain entry through the soft mucous membranes of the penis and vagina during sexual intercourse

• – blood-sucking insects inject their mouthparts through the skin and can transmit pathogens that they sucked out of an infected person

• Ex.

• The human body has three lines of defense against microbial attack:

1. External barriers

a) Intact skin acts

• Dry, dead skin does necessary for microbial growth and most

will be ejected when skin cells are constantly sloughed off

• Skin is protected by

6.3.3 Outline the role of skin and mucous membranes in defense against pathogens.

b) Membranes (in respiratory and digestive tracts)

• The mucus also that enter body through nose or

mouth• on the membranes sweep up the

mucus with microbes to be swallowed, coughed or sneezed out

6.3.3 Outline the role of skin and mucous membranes in defense against pathogens.

2. – effective against a – three categories: a) Phagocytic cells and natural killer cells

• (most important):• White blood cells that crawl around in the

extracellular fluid (similar to how amoeba

feed)• Also act as “ ” cells

(present parts of microbe to other cells of immune system)

6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.

Phagocytosis animation: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__phagocytosis.html

6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.

• :• Another class of white blood cells• Do not directly attack microbes,

• Also

6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.

b) (localized injury) – results from injury and large-scale breaches of the skin such as a cut

• Inflammation occurs:

• Injured area is walled off to isolate infected tissue:

• Phagocytes & Killer cells are recruited:

Inflammatory Response:

Skin Wound

Phagocytes move into the area and engulf the bacteria and cell debris

Capillary

Bacteria enter the wound

c) – results when

• Fever increases the

• Fever

• Fever also helps by increasing the production of

(increases resistance of surrounding cells to viral attack)

For more info on interferons: http://pathmicro.med.sc.edu/mhunt/interferon.htm

3. Immune Response (specific defenses) –

• Immune system consists of about (special type of white

blood cell) distributed throughout the body but clustered in

• Immune response results from interactions among the various types of lymphocytes and the molecules that they produce

• A successful immune response involves:1. Recognizing an invader,

2. Launching a successful attack to overcome the invader, and

3. Retaining a memory of the invader to ward off future attacks

• Some of these cells are released into bloodstream and

•

• Two key lymphocyte cells are involved in the immune response:

• Arise from

http://www.myasthenia.org.au/html/treatments.htm

• Details of the Immune Response:• Step 1:

• Antigens –

6.3.5 Distinguish between antigens and antibodies.

• Can be

(usually large proteins, polysaccharides, and glycoproteins)

• Antigens on our own cells are recognized as “ ” and do not stimulate an immune response

Macrophage

Antigen (bacteria)

B cell (lymphocyte) releasing antibodies that attack antigens

http://kids.britannica.com/elementary/art-89116/Special-cells-that-eat-antigens-are-a-part-of-natural

• The surfaces of the body’s own cells bear large proteins and polysaccharides just like microbes do• These proteins are collectively called the

• MCHs are – one person’s MHCs would be recognized as foreign antigens in another person’s body Which is why

6.3.5 Distinguish between antigens and antibodies.

• Any foreign material entering the body can act as an antigen and stimulate an immune response

• “Anti-” means & “-gen” means, so antigen is an

6.3.5 Distinguish between antigens and antibodies.

• Antibodies•

• Y-shaped molecules made of 4 polypeptides (

)• Antibodies have two sites that stick out and

constantly look for antigens (and attach to antigens) and one site that sticks to the surface of its lymphocyte

6.3.5 Distinguish between antigens and antibodies.

• Antibodies act in two ways:

1. Act as

2. Act as effectors and circulate in bloodstream

• Tips of antibodies form for antigens – each site has a specific

shape and binds only to a specific type of antigen

6.3.5 Distinguish between antigens and antibodies.

• – T-cells also have receptors on their surfaces • These are

• Act (as compared to antibodies that

act as receptors to trigger a response AND function in destroying foreign antigens)

• Details of the Immune Response:• Step 2:

– the immune system mounts two types of attacks:1. Humoral Immunity is provided by

2. Cell-mediated Immunity is produced by

Humoral Immunity

• Produced by – because antibodies circulate in the bloodstream, humoral immunity can only defend against invaders in blood and extracellular fluid

• B cells with specific antibodies on their surfaces bind to

• Binding causes B cells to divide rapidly – resulting population of cells are

6.3.6 Explain antibody production.

• Daughter cells differentiate into two cell types:

1. : do not release antibodies but play an important role in future immunity

2. : become enlarged and make huge quantities of their own specific antibodies that are released into bloodstream

6.3.6 Explain antibody production.

• Antibodies destroy microbes in four ways:

1. Neutralization – antibody may

2. Promotion of phagocytosis – antibody may

3. Agglutination – antibodies have multiple binding sites and may bind to antigens on two different microbes, holding them together

•

• This

4. Complement reactions – the antibody-antigen complex on the surface of an invading cell may trigger a series of reactions with blood proteins called the

• These complement proteins bind to antibodies and attract phagocytic cells or may directly destroy invaders by creating holes in their plasma membrane (similar to natural killer cells)

Cell-mediated Immunity

• Produced by , primary defense against

• Also important in overcoming infection by fungi or protists

• Three types of cells contribute to cell-mediated immunity:

1. Cytotoxic T-cells

2. Helper T-cells

3. Suppressor T-cells

Cytototoxic T-cells

• Release

• This attack is activated when receptors on the cytotoxic T-cell’s membrane bind to antigens on surface of infected cell – create giant holes in target cell’s membrane

Animation: http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter22/animation__cytotoxic_t-cell_activity_against_target_cells__quiz_1_.html

Helper T-cells

• When receptors of these cells bind to an antigen, the cells (hormone-like) that assist other immune cells in their defense of the body

• The chemicals released by Helper T-cells

• Very little immune response (cell-mediated or humoral) can occur without the boost provided by helper T-cells (reason why AIDS is so deadly)

Suppressor T-cells

• Act after an infection has been conquered – help to

• After infection is over, some suppressor T cells and helper T cells remain and function as memory T cells to help protect the body against future exposure to the same antigen

• Details of the Immune Response:• Step 3:

:• Memory cells allow us to retain immunity

to antigens• B and T memory cells survive for many

years

• If the body is exposed to antigens the immune system has previously encountered: The appropriate

• Second immune response is – invasion is overcome so fast, there

SECONDARY IMMUNE RESPONSE

Summary:

Summary:

• AIDS – Acquired Immune Deficiency Syndrome

• Cause: • Caused by two viruses –

• HIV is a – contains RNA as its genetic material

• AIDS describes the

6.3.8 Discuss the cause, transmission and social implications of AIDS.

• Effect:• HIV viruses

• HIV reproduces by

• Eventually the infected cell begins

• Proliferating viruses eventually

6.3.7 Outline the effects of HIV on the immune system.

• As the number of helper T-cells decline, the lymphocytes are

• AIDS does not directly kill its victims, As

the helper T-cell population declines they become more susceptible to opportunistic diseases

6.3.7 Outline the effects of HIV on the immune system.

• Transmission:

1. Sexual intercourse – virus is present in semen and vaginal secretions

2. In traces of blood on a hypodermic needle that is shared by IV drug abusers

3. Across the placenta from a mother to a baby, or through cuts during childbirth or in milk during breast-feeding

6.3.8 Discuss the cause, transmission and social implications of AIDS.

4. In transfused blood or with blood products such as Factor VIII used to treat hemophiliacs

5. Accidents causing blood contamination – the disease can be transmitted between a patient and a surgeon during operations, and between a patient and a dentist through cuts in open skin

6. Tattoos and ear piercing with infected needles

6.3.8 Discuss the cause, transmission and social implications of AIDS.

• Social Implication of AIDS: • Due to ignorance about the methods of

transmission,

• HIV positive people may have difficulty

• Sexual life styles have changed due to the awareness of and education about AIDS –

• Children may become

• May

6.3.8 Discuss the cause, transmission and social implications of AIDS.