The Role of the Circulatory System in the Body's Defence Mechanism

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Based on the Integrated Curriculum for Secondary Schools. KBSM.
Biology Form 5, Chapter 1-Transport,
1.5 The Role of the Circulatory System in the Body's Defence Mechanism.

Body's Defence Mechanisms 
Function: to protect body against disease-causing microorganisms- Pathogens.
Example of pathogens are bacteria, viruses, parasites.
Fever is part of the body's defence mechanism against infection. It increases the activity of phagocytes and combats invading microorganism.

1) State another function of circulatory system other than transport.
circulatory system also defends the body against disease-causing microorganisms. (Pathogens)

2) Three lines of defence
a) The first line of defence
b) The second line of defence
c) The third line of defence

a) The first line of defence ( Prevent pathogens from entering the body!) 

i) Physical barriers
ii) Chemical barriers

Example: 

Skin
- outer layer of the skin is tough (provides a physical barrier) that is impermeable to bacteria and viruses.
- continual shedding of dead skin cells, makes it difficult for bacteria to grow on it.
- secrets sebum, ( chemical barrier) which form a protective film over the skin.
- excreta sweat, contain an enzyme, lysozyme, which capable of breaking down the cell walls of certain bacteria.

Mucous Membrane ( that lines trachea, respiratory passageways, digestive and urogenital tracts)
- secret sticky fluid called mucus that contain lysozyme, trap and destroy bacteria.
- @nose, mucus-coated hairs, that traps and destroys pollutants from inhaled air.

Tears and saliva 
- contain lysozyme which helps protect the eyes and mouth form bacterial invasion.

WHERE can pathogens gain entry into our body?
The digestive tract. Pathogens present in the food and drinks that we consume can enter the alimentary canal. HOWEVER, stomach secrets hydrochloric acid which destroys most microorganism. 

b) The second line of defence (to prevent or overcome any invasion by pathogens!) 

Phagocytosis is a process by which phagocytic white blood cells engulf and ingest microorganisms or other particles such as cellular debris.

TWO main types of phagocytes
**Neutrophils @ blood
**Macrophages mostly found @ interstitial fluid

When infection occurs, 

1. Neutrophils and monocytes migrate to the infected area 
2. During migration, monocytes enlarge and develop into macrophages
3. They enter the interstitial fluid by squeezing through capillary walls
4. When a phagocytes encounters an invading pathogen, phagocyte ( neutrophils & macrophages) engulf the pathogen.
5. Enzyme lysozyme kills the pathogen.

Phagocytosis

c) The third line of defence (immune system)

Immune system, is a specific or targeted defence. It recognizes specific pathogens and defends the body against them.

Immunity,  mean the state in which the body is resistant to infection by a disease-causing pathogen.
For example, a virus. If you're exposed again to the particular virus, your body will recognize and destroy that virus before it can trigger symptoms of the illness. Hence, you acquire immunity after being infected by the pathogen.

Antigens, are large complex molecules ( normally a protein) that the immune system recognizes as foreign. Normally found on the outer layer of an invading microorganism. Some dissolved in blood plasma or interstitial fluid, like snake venom and bacterial toxin.

During an infection, 

1. immune system identifies the antigens invading body.
2. the antigens induce the lymphocytes to release antibodies into bloodstream to destroy particular antigen.

Antibodies, are proteins found on the surface of lymphocytes/ proteins released by lymphocytes into blood plasma.

Immune response,  the interaction between antibody and antigen which result in the antigen being eliminated from the body.

The mechanism used by antibodies to destroy antigens ( 4 types)

Agglutination 

1. Antibodies can clump pathogens together
2. The clumping makes the pathogens easy targets for phagocytes to capture and destroy.

Neutralisation

1. Antibody can neutralize the toxins produced by bacteria by binding to toxin.
2. Prevents the toxin from attaching to cells and causing damage.

Opsonisation

1. Opsonins are antibodies that bind with antigens to act as markers.
2. So that the phagocytes can recognize the antigens and destroy them.

Lysis 

1. Lysisns are antibodies that bind to antigens and cause the antigens to rupture or disintegrate.

3) State another function of lymphatic system other than returning excess interstitial fluid to the circulatory system.
Lymphocytes are distributed throughout the body in the blood and lymph. Lymphatic system also helps defend the body against invasion by pathogens  When a person has an infection, pathogens and white blood cells collect in great numbers in the lymph notes. The lymph notes may become swollen. The lymph notes contain macrophages that destroy bacteria, dead tissue, and other foreign substances by phagocytosis. They also contain lymphocytes that destroy antigens and foreign substances.

Antigen Receptor (antibody molecule antigen-binding site)
Each antibody can only bind to a specific antigen.

a) Antigen binds to the antigen-binding site of the antibody.

b) Each type of antibody can only bind to a particular type of antigen.

c) After binding to the antigen molecule, the antibody will destroy the antigen in different ways.

The Various Types of Immunity 

There two types of immunity, both types of immunity may develop either naturally or artificially:

1. Active Immunity ( means the body makes its own antibodies in response to stimulation by an antigen)
2. Passive Immunity ( means the body receives antibodies from an outside source)

Active Immunity

• does not offer immediate immunity against a disease.
• time lag between infection and a full immune response because the body needs time to make its own antibodies against a particular antigen
• usually a long-lasting immunity

Naturally acquired active immunity, once the person recovers from the infection, he will be immune if exposed to the particular pathogen again. Permanent immunity follow the infection.

Artificially acquired active immunity.

Immunisation is the process of inducing immunity by administering a vaccine. 

Vaccine is a preparation of weakened, dead or non-virulent forms of pathogen. When vaccine is injected into the body, it will activate the body to produce antibodies.Since the pathogen is modified or weakened, an individual gets mild or no symptoms of the disease. The body acquire immunity by vaccination. 

p/s: 

*For certain diseases, booster dose of the vaccine are to be given periodically. 

*1st dose usually result in the production of a low level of antibody concentration which is not sufficient to protect a person against the disease.

*The booster dose is necessary to increase antibody production to a level of immunity that protects the person against the disease.

The concentration of the antibodies in blood during first and second vaccinations

Passive immunity

Naturally acquired passive immunity

• Occurs when a foetus is still in the uterus. 
• Maternal antibodies cross the placenta to the foetal bloodstream.
• They protect the baby during the first few months after birth.
• babies can also acquire passive immunity from antibodies found in the mothers milk or colostrum during breastfeeding.

Artificially acquired passive immunity 

The difference between active and passive immunity

• involves the injection or transfusion of serum containing antibodies against the disease.
• serum which contains antibodies or antiserum from donors can be injected into a person who needs antibodies before he travels to a country in which a disease is widespread.
• these antibodies temporarily protect the person in the event of exposure to the pathogen that cause the disease.
• effective, but only lasts as long as the antibodies remain in the blood, usually about 3 months 
• short lived, offers only immediate, short term and temporary protection

AIDS

Human immunodeficiency virus (HIV) is a virus that attacks the immune system. 

Infection results in acquired immunodeficiency syndrome (AIDS).

AIDS is

• a condition in which a person who is infected experiences various infections. 
• may be symptom-free for many years (even when the virus is actively attacking the immune system)
• effects of disease may take 8-10 years to show
• due to the progressive destruction of the immune system cells

Effects of HIV on the body's defence system

• the virus reproduces inside the lymphocytes and kills them in process
• immune system is weakened, the body is prone to infections
• immune system collapses and the victim dies of an infection

Describe the transmission of HIV

• HIV enters the body through the transfer of body fluids such as blood and semen, or across placenta
• newborns can become infected with the virus from their infected mothers during delivery (usually preventable with proper medical treatment of the mother during pregnancy and delivery)
• teenagers and adults can get the disease from unprotected copulation with infected individuals
• by sharing contaminated needles used for injecting drugs or tattoo ink
• NO vaccine against HIV although certain drugs may stop the disease from progressing

HIV is not transmitted by:

• saliva, tears and sweat
• insects
• swimming in the same pool as someone who has AIDS
• shaking hands with someone who has AIDS
• sitting next to someone who has AIDS

Suggest ways to prevent the spread of AIDS 

The following answers is adopted from eHow Health, by an eHow Contributor.

1. Having protected sexual intercourse (using condoms) is about the single easiest way to protect yourself from HIV. Never have sex without one unless you are in a monogamous relationship where both partners have been tested twice. Spermicides and birth control pills are useless in preventing the spread of HIV.
2. Do not share needles. Drugs are never good, but when you share a needle, in addition to the harm the drug itself can cause, you are also putting yourself at a higher risk of catching HIV. Ending all drug use is the best possible solution.
3. A mother with HIV runs the risk of spreading the infection to her unborn child. This risk can be reduced by taking anti-retroviral drugs or a single dose of Nevrapine at delivery. Any mother with HIV should discuss the options with her doctor to help prevent spreading to her child.
4. Educate teens. The teenage years are the most susceptible to risky behavior. Talk to your teen about the dangers of unprotected sex. Answer questions they have honestly. Open communication will help your teen resist peer pressure when it comes to sex or drugs.
5. Get the whole family involved. Family activities keep the whole family busy and build strong relationships. A healthy family environment can keep teens from peer pressure by not only allowing an open door policy with mom and dad, but good ways to fill their free time.
6. Blood transfusions are another way HIV is spread. It is rare because the blood is tested, but unfortunately it can occur. Whenever possible, donate your own blood if you know you will be having a procedure that will require a blood transfusion.