The Human Defence System.docx

The Human Defence System Our bodies are constantly attacked by bacteria, fungi, viruses, and other organisms. These invaders are called pathogens. A pathogen is an organism that causes disease. There are two major aspects to our defence system – general and specific. General Defence System The first...

The Human Defence System Our bodies are constantly attacked by bacteria, fungi, viruses, and other organisms. These invaders are called pathogens. A pathogen is an organism that causes disease. There are two major aspects to our defence system – general and specific. General Defence System The first parts of the general defence system are barriers that stop the pathogens from entering the body. These barriers try to stop all pathogens therefore they are considered non-specific defences. The physical barriers of our general defence system consist of: -The Skin- A physical barrier that stops pathogens. -Clotting- If the skin is broken the blood clot stops entry of pathogens. -Sebaceous and sweat glands- These produce chemicals that kill bacteria. -Lysozyme- This is in the saliva and the tear glands. It kills bacteria. -Mucous membranes- These secrete mucus which lines many body parts. The mucous traps pathogens and prevents them from entering the body. -Nasal hairs- These remove suspended micro-organisms from the air. -Cilia- These small hairs move to force mucus to the pharynx for swallowing to the stomach. -Hydrochloric acid- This is found in the stomach. It kills micro-organisms. -The vagina- It contains bacteria that produce lactic acid that prevents the growth of pathogens. Also, the vagina has a low pH to kill bacteria as well as mucous membranes. If pathogens happen to get past the physical barriers, the General Defence System will take over. The major components of the General Defence System are: -Phagocytes: A type of white blood cell that can surround and kill microorganisms, ingest foreign material, and remove dead cells. It can also boost immune responses. (11) - Macrophages: These are large, longer living phagocytes. Some move around the body and act as scavengers while others remain in a fixed place. There are many that are present in our lymph system. - Complement Defence Proteins: These are substances produced by other proteins, or in response to the presence of foreign material in the body, and that trigger or participate in a complement reaction. This is a reaction to the presence of a foreign microorganism in which a series of enzymatic reactions, triggered by molecular features of the microorganism, result in the bursting or engulfing of the pathogen. -Interferons: These are defence proteins that are produced by body cells that are infected by a virus. They travel to nearby cells and prevent the spread of the virus. -Inflammation: Cells that have been infected produce a chemical called histamine. This chemical causes the blood capillaries to dilate and become more porous. As a result, the area swells, gets red, becomes warm, and is painful. This results in more white blood cells coming to the area to fight the infection. If the inflammation happens over the whole body, a fever develops. The fever is the body’s way of combating bacteria and viruses. The higher temperature inhibits the pathogen from reproducing. Specific Defence System The Specific Defence System recognises and coordinates attacks against specific pathogens. -White Blood Cells: Lymphocytes and monocytes are produced in the bone marrow. They are then transported by the blood to lymph vessels, lymph nodes, the spleen, or the thymus gland. (i) Monocytes- White blood cells that become macrophages. These are large white blood cells that engulf invaders. Once engulfed, part of the invader remains on the surface of the microphage. This is called an antigen. Antibodies are produced to fight off future invaders. (ii) Lymphocytes- Some attack body cells that have antigens on their surface. Other lymphocytes produce antibodies. -Antibodies: Lymphocytes produce antibodies because of antigens. These are proteins in the group called immunoglobulins. Each antigen will only stimulate the production of one specific antibody that will fit into its receptor area. This is called natural active induced immunity. It is protection gained against a particular pathogen by the production of specific antibodies after the antigen on the pathogen has been detected. (12) Antibodies act in a variety of ways, including: a. Some bind to the antigens on the surface on the pathogens. This prevents the pathogen from entering the host cell. b. Others cause the pathogens to clump together. Phagocytes then engulf the clumped pathogens. c. Some antibodies activate the complement system which then acts to burst the pathogen. This antibody protection remains in our bodies. When the same pathogen invades, the antibodies are quickly produced because some of the lymphocytes from the previous invasion are still present. We may get various types of illnesses that present the same as previous illnesses. This is because there are different forms of the same illness. For example, colds. Different pathogens may produce colds. When this occurs, our body must produce new antibodies to attach to those specific antigens Autoimmune diseases occur when the defence system produces antibodies against itself. Examples of this include Rheumatoid Arthritis and Multiple Sclerosis. Allergies occur when the defence system produces antibodies against non-invaders. The immune system perceives a harmless substance as a threat and produces antibodies resulting in allergies. Examples of this include Hay-fever and Asthma. -Artificial active immunity: In this type of immunity the person is inoculated with a non-diseasing causing part of the pathogen. This can be a part of the pathogen or a dead pathogen. This will carry the antigen that will trigger the production of antibodies. This is called a vaccination. Genetic engineering is now producing antigens that can be inoculated into people. The antibodies form without any risk to the person. Vaccines The first vaccine was produced by Edward Jenner in 1796. He discovered a vaccine that produced antibodies against smallpox. There are different types of vaccine, including; 1. Preparation of the dead pathogen. 2. Preparation of the live but weakened pathogen. 3. Preparation of a close but relatively harmless relative of the pathogen. 4. Preparation of parts of the pathogen that carry the antigen. -Natural Passive Immunity: This occurs when a child gets antibodies from the mother either before it is born or in the mother’s milk. This type of immunity only lasts a few months. -Artificial Passive Immunity: This occurs when a person is injected with antibodies made by another organism. A tetanus shot is an example. The antibodies are gotten from horses. This immunity lasts only a short time. (13) Types of Lymphocytes Lymphocytes are either B-cells or T-cells depending on where the cells matured. B-cells mature in the bone marrow while T-Cells mature in the Thymus gland. -B-cells: B-cells work in the lymphatic system, especially the spleen and lymph nodes. Each B-cell works on 1 specific antigen therefore, producing only 1 type of antibody to that specific antigen. A B-cell will come into contact with the antigen and then reproduce rapidly. These rapidly produced cells are called plasma cells. These last only a few days but are extremely effective. Most of these B-cells die within a few days but others remain alive. They are called Memory B-cells. When the same antigen presents in the organism, these memory B-cells are already there to begin the production of plasma cells and antibodies. This is called a secondary B-cell response. This is more effective than the original B-cell response for the following reasons: a. The antibodies are produced to a smaller amount of antigen. b. The antibodies are produced much faster. c. More antibodies are produced than in the original response. -T-cells: These defenders are produced in the bone marrow but become activated in the thymus gland. These cells do not produce antibodies but protect us in the following ways: a. Helper T-cells: They recognise antigens on the surface of other white blood cells, especially macrophages. The Helper T-cells enlarge, multiply, and form a group of Helper T-cells. This group will produce chemicals including interferon and stimulate the formation of B-cells. They also stimulate the reproduction of Killer T-cells. b. Killer T-cells: These cells destroy abnormal body cells such as virus-infected cells and cancer cells. They are stimulated by Helper T-cells. These cells release a protein called perforin. These proteins form pores in the membranes of the cells they attack. Water and ions from the surroundings flow into the cells and burst them. This is called lysis. c. Suppressor T-cells: These cells suppress or inhibit from working after the pathogen has been destroyed. d. Memory T-cells: Many of these cells survive for life. They stimulate Memory B-cells to produce antibodies. Others stimulate the production of Killer T-cells. Both memory cells are responsible for lifelong immunity.