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Transcript
Human Defence system 4. An Immune System Pathogens are micro-organisms that cause disease. Immunity is the ability of an organism to resist infection. Invaders How does the body defend itself from being infected from disease by pathogens? Part a – GENERAL DEFENCE SYSTEM How does the body defend itself from disease? the blood stream If we consider the human body, the infection will spread around the body if it reaches our transport system. How do microbes enter the body? eyes ears mouth nose skin cuts genitals A number of these places where microbes can enter the body are defended. Mouth Defence in our stomach If microbes enter through the mouth (usually on food) they will be swallowed and enter the stomach. Within the stomach is hydrochloric acid, which will kill them. Nose Defence our breathing system Cells lining our breathing system are called cilia produce mucus in which microbes can become stuck. The cilia then send the mucus (including the trapped microbes) towards the mouth and nose where they are either swallowed or coughed up. microbes travelling down the trachea within inhaled air ciliated cells microbes become stuck within the mucus mucus being made by the ciliated cells Elevator action coughed out swallowed Defence by our skin Skin thick layer of skin blood capillary Microbes have to penetrate the layer of skin that covers the entire surface of our body. Once through this, they can then reach the blood system. Cuts When you cut the skin, the blood system is exposed to the air. Microbes could then get into the blood. To limit this problem, the body can quickly heal wounds by firstly clotting the blood and secondly forming a scab over the wound to shield the blood from the air. Once the scab has formed, the body repairs the damaged tissue underneath and finally fresh skin tissue is formed. If the cut is very deep, a scar will remain after the cut has healed. exposed blood vessel cut scab has formed over the wound microbes cannot gain entry new tissue being formed Different defence mechanisms General defence system These barriers try to stop all pathogens (non-specific defences). 1. Barriers to entry: The skin secretes chemicals from the sebaceous glands that harm or kill bacteria. The respiratory, reproductive and digestive tracts secrete mucus that may remove foreign particles. Composition of Blood Solids Liquid Plasma Red Blood Cells White Blood Cells Platelets General defence system consists of: 2. White blood cells called phagocytes ingest harmful foreign objects and destroy them White Cells Defenders Part B – SPECIFIC DEFENCE SYSTEM Our Specific Defence System - attacks specific invaders This involves an antigen-antibody response, and uses specialised white blood cells, called lymphocytes and monocytes both made in the bone marrow. Antigens are foreign molecules capable of triggering an antibody response. Germ (antigen) Antibody monocyte “Eating ” germ Monocytes Monocytes are phagocytic These engulf a microorganism upon contact. Monocyte Germ “Eating” germ Once engulfed part of the invader remains on the surface of the monocyte as an antigen. Monocyte engulfs an invader Monocyte engulfs a bacterium 2. Lymphocytes Can either attack infected cells or produce antibodies lymphocyte An antibody is a protein which sticks to an antigen and marks it for destruction by other defence cells 1. Lymphocyte notices antigen and produces antibodies to fit the antigen shape 2. Antibody “ clamps” the antigen antigen site antibody 3. Cells with antigen become immobilised (cant divide or spread) and are also marked for destruction The Clampers Antigen Antibody Matching microbes and antibodies Passive and Active immunity Induced immunity Protection from a disease due to the presence of an antibody. passive. active Natural Antibodies develop after infection Artificial Antibodies develop after vaccination LONG TERM IMMUNITY A vaccine is a dead microbe that is injected into the body and triggers antibodies but does not cause the disease. Induced immunity Protection from a disease due to the presence of an antibody passive. active Natural Artificial Getting the antibodies Getting the from elsewhere Antibodies from naturally elsewhere e.g. in the womb, or medically e.g. from mother’s milk. injection Mother’s antibodies SHORT TERM IMMUNITY Review and put class into context Phagocytic Cells General Defence System Skin Barrier System Respiratory Tract Digestive Tract Defence System in Humans Invading Organism s Reproductive Tract Specific Defence System Defence Molecules Defence Cells Lymphocytes – more detail Higher level only Higher level – Lymphocytes in more detail T lymphocytes ( also called T cells) Mature in the Thymus but work in the lymph nodes T cells do not produce antibodies. Types of T lymphocytes helper T cells 1. recognise antigens, 2. enlarge, 3. secrete chemicals such as interferon that stimulate production of B cells killer T cells attack infected cells containing a foreign antigen, secrete a chemical called perforin that perforates the membranes of cells ; suppressor T cells stop the immune response after the pathogen has been destroyed. memory T cells They memorise the antigen and circulate in the body for years B lymphocytes B lymphocytes mature in the bone marrow, before moving to the lymph nodes, When a B cell encounters matching antigen, they divide into plasma and memory cells. plasma cells produce antibody molecules, that bind to antigens, immobilse pathogens and mark them for destruction B memory cells memorise the antigen and circulate in the body for years Memory B cells do not engage in that first battle. They circulate in the body for years, and can intercept antigens quickly if they enter the body for a second time. Monocyte Monocyte