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    Science education: The body’s defence against disease (17 april)

    THE IMMUNE SYSTEM – THE BODY’S DEFENCE AGAINST DISEASE (17 APRIL)

    The role of the immune system is to protect the body from bacteria, viruses and tumours. so exactly how does it do that? Some of the question that will be covered in this coming Friday's SCIENCE EDUCATION post include:-

    • What's the relevance of blood to fighting infections?
    • What do we mean by immunity?
    • What's the difference between an antibody and an antigen?
    • Why are transplanted organs often rejected? What do we mean by organ rejection?
    • Why do we have to check a person's blood group/type before giving a blood transfusion?
    • What's the connection between the immune system and allergies?
    • How do vaccines work to prevent infection?
    • What are antitoxins?
    • Why is HIV/AIDS so difficult to treat?
    The Following 2 Users Say Thank You to SHAMAS For This Useful Post: dilkumar,XenoEnsi-14


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    Re: Science education: The body’s defence against disease (17 april)

    Interesting subject. Look forward to reading it.

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    Science education: The immune system

    THE IMMUNE SYSTEM – THE BODY’S DEFENCE AGAINST DISEASE



    The role of the immune system is to protect the body from bacteria, viruses and tumours. The immune system deals with these threats in a number of different ways, from engulfing bacteria to killing parasites, tumours and cells infected with viruses.

    Before we examine the immune system in detail, we ought to acknowledge that the body has a variety of ways of preventing our bodies being invaded by micro-organisms. A few examples are cited below.

    • The skin is not only made of a tough protein called keratin which acts as a physical barrier, but the shedding of skin also helps to dispose of bacteria on the skin. Furthermore the skin secretes sebum, an oily substance from the sebaceous glands, which inhibits the growth of many harmful bacteria.

    • The eyes produce tears laced with an enzyme lysozyme which digests the bacterial wall of many micro-organisms.

    • The nose and lungs filter bacteria through the hairs/cilia and the phlegm like secretions of the bronchioles.

    • Generally the pH of the vagina is acidic and inhibits bacterial growth

    • Ear wax has antibacterial properties and reduces the risk of bacterial invasion of the body through the ears.


    Haematocrit
    Whole blood is composed of plasma (liquid), cells (white blood cells) and platelets, which cause blood to clot. If whole blood is placed into a tube and centrifuged, the cells and the plasma will separate into distinct layers. The red blood cells (erythrocytes), which are heavy, will pack into the bottom of the tube, the (yellowish coloured) plasma will be at the top of the tube, and the white blood cells (leukocytes) and platelets will form a thin layer (buffy coat) between the red blood cells and the plasma. The haematocrit is defined as the percentage of whole blood made up of erythrocytes. This value is determined by dividing the height of the erythrocytes by the total height of the blood in the tube and multiplying by 100.The haematocrit is useful in diagnosing certain medical conditions.



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    Haematocrits vary depending on sex and environmental conditions, but there is a range of values that is considered normal. Average haematocrit values are:

    Males.......... 40-50%
    Females....... 38-45%
    Athletes........ > 50%

    Any activity or condition that consistently lowers oxygen levels in the blood will cause a rise in the haematocrit.

    1. Components of the immune system
    The following organs make up the immune system:

    a. Bone marrow (which produces all the different cell types in the blood)
    b. Thymus
    c. Spleen
    d. Lymph nodes

    A key part of the immune system are the white blood cells which are produced by bone marrow and help the immune system to perform its role.

    a. Bone marrow
    Bone marrow is a spongy tissue found within bones. Bone marrow is responsible for producing red and white blood cells. White blood cells play an important role in how the body fights infection.

    b. Thymus
    The thymus is an organ located between the heart and the breast bone. The thymus produces hormones involved in the immune system and is also responsible for the maturation of powerful immune cells called lymphocytes.

    c. Spleen
    The spleen is located between the stomach and the diaphragm and performs a number of activities for the immune system. The spleen filters bacteria and viruses out of the blood and stores red blood cells and lymphocytes for release when required. For example, if the body contracts an infection, the spleen can release a ready supply of lymphocytes to control the infection.

    d. Lymph nodes
    The lymph nodes are situated at several parts of the body including at the:

    • Neck
    • Armpits
    • Groin
    • Abdomen
    • Pelvis
    • Chest

    The lymph nodes filter the lymph fluid and white blood cells attack any bacteria or viruses that are present.

    Note: the tonsils and adenoids are also lymph tissues which filter germs as the try to enter the body through the mouth and nose. Sometimes these tissues become inflamed because of the role they play. Only if repeated inflammations are occurring might the doctor suggest the tonsils or adenoids be removed.


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    HOW THE IMMUNE SYSTEM WORKS

    Your immune system uses a huge army of defender cells - different types of white blood cell. You make about 1000 million of them every day in your bone marrow. Some of these cells, called macrophages, constantly patrol your body, destroying germs as soon as they enter. This is your 'natural' or inborn immunity. But if an infection begins to take hold, your body fights back with an even more powerful defence of T- and B-cells. They give you acquired immunity, so that the same germ can never make you as ill again.

    White Blood Cells Types and Functions



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    White Blood Cells
    White blood cells are the cells that help the body fight infection. There are a number of different types and sub-types of white blood cells which each have different roles to play. The three major types of white blood cells are:

    1. Granulocytes
    2. Monocytes
    3. Lymphocytes

    1. Granulocytes
    Granulocytes are phagocytes that is they are able to ingest foreign cells such as bacteria, viruses and other parasites. Granulocytes are so called because these cells have granules of enzymes which help to digest the invading microbes. Granulocytes account for about 60% of our white blood cells.

    There are three different forms of granulocytes:


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    • Neutrophils

    Neutrophils are by far the most prevalent of these cells. Each neutrophil cell can ingest up to between around 5 and 20 bacteria in its lifetime.

    • Eosinophils

    Eosinophils are involved in allergic reactions and can attack multicellular parasites such as worms.

    • Basophils

    Basophils are also involved in allergic reactions and are able to release histamine, which helps to trigger inflammation, and heparin, which prevents blood from clotting.

    2. Monocytes

    Monocytes can develop into two types of cell:

    • Dendritic cells are antigen-presenting cells which are able to mark out cells that are antigens (foreign bodies) that need to be destroyed by lymphocytes.

    • Macrophages are phagocyte cells which are larger and live longer than neutrophils. Macrophages are also able to act as antigen-presenting cells.

    3. Lymphocytes

    Lymphocytes are cells which help to regulate the body's immune system. The main types of lymphocytes are:

    • B lymphocytes (B cells)
    • T lymphocytes (T cells)


    What do T- and B-cells do?
    T- and B-cells are highly specialised defender cells - different groups of cells are tailored to different germs. When your body is infected with a particular germ, only the T- and B-cells that recognise it will respond. More on this a little later.

    Natural Killer Cell



    ANTIGENS & ANTIBODIES: RECOGNISING YOUR OWN CELLS

    Any substance (bacterium, virus or protein) that causes the immune response to be triggered, is called an antigen. All our cells have proteins on the surface. These proteins are recognised by specialised white cells, and hence the immune system does not attack your own cells.

    In certain auto-immune diseases (e.g. Hashimoto’s Disease) some of your own body cells are not recognised i.e. they are considered as ‘foreign’ cells, and therefore specialised white blood cells attack these tissues causing illness. This immune response triggers inflammation. In rheumatoid arthritis, the layers of cells lining the joints are affected. This causes stiffness, swelling and pain.

    A foetus growing in the womb, is clearly composed of cells ‘foreign’ to the mother. So why do the white blood cells of the mother not destroy the foetus? To avoid destruction the antigens on the cell surfaces of foetal cells, are disguised or shielded. The surface proteins are covered up! When the foetus reaches full term and is born, this shielding disappears.

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    An antibody (Ab), also known as an immunoglobulin (Ig), is a large Y-shape protein produced by plasma cells and is used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, called an antigen. Each tip of the "Y" of an antibody contains a paratope (a structure analogous to a lock) that is specific for one particular epitope (similarly analogous to a key) on an antigen, allowing these two structures to bind together with precision. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly.

    Antibodies are glycoproteins belonging to the immunoglobulin superfamily; the terms antibody and immunoglobulin are often used interchangeably. Antibodies are typically made of basic structural units - each with two large heavy chains and two small light chains. There are several different types of antibody heavy chains, and several different kinds of antibodies, which are grouped into different isotypes based on which heavy chain they possess. Five different antibody isotypes are known in mammals, which perform different roles, and help direct the appropriate immune response for each different type of foreign object they encounter.

    Though the general structure of all antibodies is very similar, a small region at the tip of the protein is extremely variable, allowing millions of antibodies with slightly different tip structures, or antigen-binding sites, to exist. This region is known as the hypervariable region. Each of these variants can bind to a different antigen. This enormous diversity of antibodies allows the immune system to recognize an equally wide variety of antigens.

    The large and diverse population of antibodies is generated by random combinations of a set of gene segments that encode different antigen-binding sites (or paratopes), followed by random mutations in this area of the antibody gene, which create further diversity. Antibody genes also re-organize in a process called class switching that changes the base of the heavy chain to another, creating a different isotype of the antibody that retains the antigen-specific variable region. This allows a single antibody to be used by several different parts of the immune system.

    What is so special about your T-cells?
    Having recognised the invader, different types of T-cell then have different jobs to do. Some send chemical instructions (cytokines) to the rest of the immune system. Your body can then produce the most effective weapons against the invaders. Other types of T-cells recognise and kill virus-infected cells directly.

    What is so special about your B-cells?
    B-cells make antibodies (special Y-shaped proteins), which circulate and bind to antigens. Antibodies stick to antigens on the surface of germs, stopping them in their tracks, creating clumps that alert your body to the presence of intruders. Your body then starts to make toxic substances to fight them. Patrolling defender cells called phagocytes engulf and destroy antibody-covered intruders.


    Why You Are Still Alive - The Immune System Explained



    VACCINATION

    To become permanently immune to many illnesses, you must either catch it, or be vaccinated against it. The first child ever to be vaccinated was James Phipps in 1796. The English doctor Edward Jenner injected him with cowpox, which made him immune to smallpox, a similar but far more deadly disease. These days, more than half the children in the world are given vaccines against whooping cough, diphtheria, tetanus, polio, measles and tuberculosis. Currently there are hardly any anti-viral drugs to fight a viral infection once it takes hold. (This is the reason why doctors generally do not prescribe medicines for viral chest infections, or even influenza. The cold/flu remedies taken by patients are about relieving the symptoms of the infections rather than tackling the virus itself.)

    Vaccine works by triggering part of the immune response – the recognition of the invader (antigen). The reason you don’t become ill due to the bacteria/virus you were inoculated with, is that the smallpox or polio virus has been chemically treated to render it harmless. Once your immune system learns to recognise the disease organism, your body can rapidly produce antibodies against it if you are infected with the active disease organism. The disease organism will not survive long enough in the body to overwhelm you and cause you to become ill. The influenza and other vaccinations work in the same way. (Anti-toxins will be discussed a little later in this topic.)

    Vaccinations of this kind produce permanent immunity to those specific infections (antigens.) This type of immunity is often called active immunity (as opposed to the passive immunity discussed later.)Because the influenza virus mutates rapidly, every year, there numerous new varieties of influenza virus. This is why it is necessary to immunise against influenza every year. In the UK, influenza vaccine against the nastiest strains of influenza, is available free to children (including secondary school children) and to the people aged 60 or over, and those suffering from asthma, and cardiovascular diseases. However if you do not fall into these categories, many pharmacies provide the vaccine at a cost of less than Ł10. (Well worth it!)

    How does breast milk protect babies?
    As a new-born baby, you had some temporary immunity passed on from your mother, both in the womb and via breast milk. She supplied you with antibodies to fight infections. The antibodies in breast milk are not digested by stomach acid, unlike most proteins. This type of immunity is not provided by artificial milk and that is one of the major reasons doctors recommend breast-feeding babies instead of bottle feeding them.

    Transplant of Organs
    Each of your cells carries molecules called antigens on their surface, which identify them as part of your body. Cells from someone else's body will have different antigens, so your immune system will treat them as if they were invading germs. To carry out blood transfusions or organ transplants, doctors must try and find a donor whose antigens are as similar as possible to those of the patient. If the match is not good, the body will reject the transplant i.e. will attempt to destroy it. Drugs which suppress the immune system are often prescribed for recipients of organs transplants.

    Blood Groups & the Immune System
    The ABO blood classification system is based on two different antigens, A and B, found on the surface of red blood cells. You may have one, both, or neither of these antigens. Group AB people, the least common in the UK, have both. Group O, the most common, have neither. If you were to receive blood that contained an unfamiliar antigen, antibodies in your own blood would clump the donated cells together and you would die. In the early days of blood transfusions when none of this was understood, whether transfusions were successful or not was entirely down to chance – since doctors didn’t know what kind of blood the patient had or the kind that was being transfused. Since blood group O contains no antigens, it can be given to any person regardless of their blood group. Not surprisingly, people with blood group O are called universal donors. Each blood group is further subdivided into Rhesus positive and Rhesus negative (since these were first discovered in Rhesus monkeys.)

    Anti-toxins
    Some diseases like cholera and tetanus cause problems for the body because of the toxins the bacteria release. In fighting these sorts of diseases the toxins need to be neutralised. One way of doing this is to use the toxin to trigger an immune response to generate the specific antibodies that can counter the toxin. However, this would be dangerous to the patient. To overcome this difficulty, a very dilute does of the toxic is injected into an animal (e.g. horse) and over a few days the horse will produce specific antibodies (anti-toxin proteins). Blood can be drawn from the animal and the anti-toxin separated out. This is then injected into a patient suffering the disease, or used as a preventative measure. Note that this anti-toxin will only remain in the body for a few years. The anti-toxin provides only temporary immunity. Since your own immune system was not involved in recognising the antigen, we call this type of protection, passive immunity. This also explains why doctors sometimes inject people with antibodies to provide short-term protection from hepatitis, tetanus, choler etc. for example.

    The process described above is used to produce snake anti-venom. When a patient is suffering from the effects of snake venom, an injection of the (specific) anti-venom can be used to treat the patient.

    Allergies
    The substance causing the allergy is called an allergen. Allergies occur when the allergen is considered by the body to be an antigen or invader. In this situation, an immune response is provoked, producing some of the symptoms associated with the condition.

    One in five people in the UK suffer from hay fever, an allergy to pollen. Others are allergic to dust mites, nuts, strawberries or bee stings. Your body generally tries to get rid of anything that is an allergen. That is why some allergens cause vomiting or diarrhoea. In some people an allergen trigger an immunological reaction. Medical opinion puts some allergies down to a lack of exposure (or challenge) to the immune system in the early few years of life. Because many children live in very clean environments, they are not exposed to a range of fairly harmless germs and hence the body does not properly learn to distinguish between infectious agents and allergens.

    AIDS & the Immune System
    Doctors in the US first reported a new disease, AIDS (acquired immune deficiency syndrome), in 1981. It has since become a world-wide epidemic. AIDS is caused by the human immunodeficiency virus (HIV), which attacks the immune system itself, thereby disarming the body's defences against infections and certain cancers. Germs that normally cause minor illnesses in healthy people can make people with AIDS very ill and even cause fatalities. The observation that patients were dying of diseases that are generally not fatal alerted doctors that something else was the underlying cause of death.

    HIV attacks and kills crucial immune system cells, known as T-helper cells. Without T-helper cells (which kill cells that have been infected with germs) many other immune system cells cannot not work properly, including B-cells that make antibodies. A person infected with HIV may not show any symptoms for years. But untreated, the number of T-helper cells steadily drops. Eventually, the numbers fall so low that the risk of infection greatly increases, and the symptoms of AIDS appear.

    Several drugs are now available to treat HIV infection. Some, including AZT, interfere with the virus as it tries to copy itself inside the immune system cells. Other drugs stop the virus maturing and leaving the cells. None of these drugs can cure HIV infection or AIDS, although when used in combination they can delay the appearance of symptoms, perhaps indefinitely. However, not everyone in the world infected with HIV can afford, or get access to, these drugs.

    HIV spreads most commonly through unprotected sexual contact with an infected partner. It can also spread through contact with infected blood, usually through needle sharing amongst drug users. Mothers can pass HIV on to their babies, though the risk of this is much lower if anti-HIV drugs are taken during pregnancy. Scientists are finding it difficult to produce a vaccine against HIV as the surface of the virus constantly changes. So currently the only way to prevent infection is to avoid contracting the virus.

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    Re: Science education: The immune system

    [MENTION=2]Aryan_B[/MENTION]

    Bro, you'd gone and done it again! Why did you remove this post from the science/tech section? This is not an announcement!

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    Re: Science education: The immune system

    Quote Originally Posted by SHAMAS View Post
    [MENTION=2]Aryan_B[/MENTION]

    Bro, you'd gone and done it again! Why did you remove this post from the science/tech section? This is not an announcement!
    Must have been one of the other mods. I have put it into Science section now.

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    Science Editor SHAMAS's Avatar
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    Re: Science education: The immune system

    [MENTION=2]Aryan_B[/MENTION]

    Thanks.

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