Disease and body defences

• Bacteria, fungi and viruses can cause diseases in man.
• An organism which causes a disease is called a pathogen and it is described as pathogenic.
• a disease which can be passed on from one person to another is called a communicable or infectious disease.
• Diseases caused by bacteria include salmonella, tuberculosis and chlamydia.
• diseases caused by viruses include HIV , colds /flu , HPV, covid
• diseases caused by fungi include athletes foot and potato blight
• Bacteria diagram

  
• virus diagram

  
• chlamydia is caused by bacterium and it is spread by unprotected sexual intercourse. you can prevent spread by using a barrier method such as a condom. The treatment is antibiotics
• salmonella is caused by bacterium (food poisoning) and it is spread by contaminated food due to poor hygiene and undercooking. It can be prevented by cooking food well, defrosting food, washing your hands and not mixing raw and cooked foods. the treatment is rehydration and antibiotics.
• the disease tuberculosis is caused by bacterium and it is spread through the air(airborne) and coughing and sneezing (droplet infection) you can prevent it by getting the BCG vaccine and the treatment is antibiotics.
• HIV (leading to aids ) is caused by a virus and it is spread by blood to blood contact, infected blood products , sharing needles and unprotected sexual intercourse. It can be prevented not sharing needles and screening blood products and the treatment is antiviral drugs and a barrier method (condom)
• a cold/ flu is caused by a virus and it is a droplet infection so it is spread by coughing and sneezing. It can be treated with rest to reduce symptoms and a vaccine / antibiotic
• HPV(leading to cervical cancer) is caused by a virus and is spread by unprotected sexual intercourse and skin to skin contact of the genital areas. it can be prevented by getting the HPV vaccine and using a barrier method. the treatment is cryotherapy / cream or cancer treatment.
• athletes foot is caused by fungi and it is spread because of contaminated floors (swimming pools ) or sharing sock and shoes. it can be prevented by keeping your feet dry and avoiding contamination. the cure is fungal creams.
• potato blight is caused by fungi and it is spread because of wind and soil water. it can be prevented using blight resistant varieties of potatoes and the cure is fungicide.
• disease causing organisms are called pathogens
• for pathogens to spread disease they must enter the body and multiply
• most infectious diseases are caused by microbes , in particular bacteria and viruses
• the nasal cavity prevents the entry of pathogens because of the mucus membranes and the hair that filters the air and the mucus traps microbes
• skin prevents the entry of pathogens because it is a dead dry level of cells which acts as a barrier to prevent the entry of microbes.
• the respiratory passages prevent the entry of microbes because they have ciliated epithelium to waft bacterial trapped in mucus out of the lungs
• if the skins barrier is broken a blood clot forms which stops blood escaping and prevents further entry of micro organisms
• white blood cells are part of the body's immune system. The 2 main types of white blood cells are lymphocytes and phagocytes.
• White blood cells recognise the pathogens as being foreign because they have different proteins on their cell surface called antigens.
• an antigen is a foreign protein on a cell surface that stimulates antibody production.
• pathogens have antigens that stimulate the lymphocytes
• lymphocytes recognise the foreign antigen on the pathogen and they produce and release proteins called antibodies
• antibodies and antigens have a complementary shape so the antibodies bind to the antigens on the surface of the pathogen.
• each antibody is specific to one antigen so different antibodies are needed for different diseases
• After the antigens and antibodies have bonded together the pathogens clump together and this prevents them from spreading and it makes phagocytosis easier for the phagocytes.
• The process of antibodies fighting against the pathogens may take several days if this is the first time the pathogen has infected the body so symptoms may appear
• the first encounter with the pathogen (microorganism) causes the production of memory lymphocyte cells. These remain in the body for a long time and will respond immediately and rapidly produce high levels of antibodies to match the antigens on the pathogen if a re-infection occurs. Symptoms are unlikely to develop.
• An antibody is a protein produced by a pathogen that is complementary to the shape of an antigen and they bind to antigens on the surface of a pathogen to immobilise it and stop it from spreading.
• phagocytes recognise the clumps of bacteria and engulf and digest the pathogens using enzymes. this process is called phagocytosis.
• immunity means that a persons antibody levels are high enough to protect them from disease if a a micro organism enters the body. Most people are immune to a number of diseases.
• The effect of a first infection on antibody levels is called the primary response.
• when a pathogen infects the body for the first time there will be a slight delay while the lymphocytes recognise the antigen. Then antibody levels will increase gradually to the point of immunity and and then the levels will slowly decline as the antibodies are used up.
• the level of antibodies in the blood slowly decreases over time but exposure to a second infection of the antigen causes antibody levels to increase again and this is called the secondary response.
• in a secondary response to to an infection there is no time delay for the lymphocytes to recognise the antigen because of the presence of the memory lymphocyte which divide and begin antibody production immediately. the rise in antibodies is rapid and the levels decrease more slowly.