Health and Disease Part Two - Unit 2 OCR

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  • Health and Disease - Part Two
    • Immunity, Vaccinations and Developing Drugs
      • Active and Passive Immunity
        • Active - when your immune system makes its own antibodies after being stimulated by antigens, can be natural : when you become immune after getting disease, or artificial : become immune after given a vaccination containing harmless dose of antigen
        • Passive - being given antibodies made my different organism so immune system doesn't produce any, can be natural : baby becomes immune due to antibodies received from mother through placenta or breast milk, or artificial : immune after being injected with antibodies from someone else
        • Active - exposure to antigen, takes a while for protection to develop, long-term protection, memory cells produced
        • Passive - no exposure to antigen, protection is immediate, short-term protection, memory cells not produced
      • Vaccination  - while B lymphocytes are busy dividing to build up numbers to deal with pathogens you suffer from disease, this is where vaccinations can help
        • Vaccines contain antigens that cause body to produce memory cells against particular pathogen without it causing disease, this means you become immune without getting any symptoms and the antigens may be free or attached to dead or attenuated pathogen
          • May be injected or taken orally, disadvantages of oral is that it could be broken down by enzymes in gut or molecules of vaccine may be too large to be absorbed in blood, sometimes booster vaccines are given later on to make sure more memory cells are produced
            • If most people in community are vaccinated the disease becomes externally rare meaning that people who haven't been vaccinated are unlikely to get the disease as there's no one to catch it from - called herd immunity
      • Problems  with Development - vaccinating against disease isn't always straightforward, some pathogens can change their surface antigens so when you're infected the memory cells produced following the vaccine will not recognise the different antigens, immune system then has to start from scratch and carry out primary response
        • E.g. Influenza - proteins on surface of virus act as antigens triggering immune system, antigens can change regularly forming new strains of virus
          • Every year there are different strains of virus circulating in population so different vaccines have to be made, labs collect samples of strains (such as WHO [World Health organisation] and CDC [Centre for Disease Control]) and test effectiveness of different vaccines
            • New vaccines are developed and one is chosen per year that's most effective against recent virus, governments and health authorities then implement a programme of vaccination using most suitable, good example of how society uses science to inform decision making
      • Sources of Medicines - changing antigens means some pathogens can rapidly develop resistance so scientists need  to be constantly developing new drugs to target resistant strains of pathogens while developing drugs for diseases that are currently incurable
        • Many medicinal drugs are manufactured using natural compounds found in plants animals or microorganisms: penicillin is obtained from fungus, some cancer drugs made using soil bacteria, daffodils are grown to produce drug used for Alzheimer's
          • Only small proportion of organisms been investigated so far so it's possible plants or microorganisms exist that contain compounds that could treat incurable diseases
            • Possible sources of drugs must be protected by maintaining biodiversity on Earth, if not protected then some species could die out before we have a chance to study them, even organisms already been studied may still prove to be useful sources of medicine as new technology are developed for testing and identifying
    • Infectious Diseases
      • Malaria - parasitic disease caused by Plasmodium : a genus of eukaryotic single-celled parasites
        • Transmission - Plasmodium parasites are transmitted by mosquitos (insects that feed on blood of animals), particularly female Anopheles mosquito that carries parasites, mosquitos are vectors as they don't cause the disease themselves but spread the infection by transferring parasites from one to another, they transfer Plasmodium into animal's blood when feeding
        • Infection - Plasmodium infects liver cells and red blood cells, it disrupts blood supply to vital organs and has a complex life cycle with multiple stages
          • 1. Mosquito feeds and injects immature Plasmodium parasite into host animal
            • 2. Plasmodium travels to the host's liver where they infect hepatocytes
              • 3. Plasmodium multiply in the hepatocytes
                • 4. The Plasmodium parasites mature and hepatocytes burst releasing parasites into blood stream
                  • 5. The mature Plasmodium parasites infect erythrocytes
                    • 6. The mature parasites replicate in the erythrocytes
                      • 7, The mosquito feeds taking up the parasites
                        • 8. Plasmodium reproduce in the mosquito and immature parasites are formed
                          • 1. Mosquito feeds and injects immature Plasmodium parasite into host animal
                            • 2. Plasmodium travels to the host's liver where they infect hepatocytes
                              • 3. Plasmodium multiply in the hepatocytes
                                • 4. The Plasmodium parasites mature and hepatocytes burst releasing parasites into blood stream
                                  • 5. The mature Plasmodium parasites infect erythrocytes
                                    • 6. The mature parasites replicate in the erythrocytes
                                      • 7, The mosquito feeds taking up the parasites
                                        • 8. Plasmodium reproduce in the mosquito and immature parasites are formed
          • Preventing and Treating - number of medicines but hundreds still die each year so scientists are trying hard to find a way to prevent disease, best solution would be vaccination but difficult for a number of reasons
            • Plasmodium parasite spends most of life cycle hidden inside human cells, only exposed in bloodstream for short period of time which doesn't give immune system much time to recognise and destroy it
            • Four different species of Plasmodium, mutation and variation cause each species to have different antigen so need different vaccines
            • Plasmodium life cycle involves more than one stage, different stages have different antigens so vaccine against one stage won't protect against another, not much opportunity for immune system to act on each one as stages are short
            • Protection can include mosquito nets, pesticides and education of early signs and symptoms so treated early before spread
        • Tuberculosis (TB) - lung disease caused by bacterium Mycobacterium tuberculosis
          • Transmission - droplet infection meaning when infected person coughs or sneezes tiny droplets of saliva and mucus containing bacteria is released, these droplets breathed in by another to cause infection
            • Due to way it is transmitter it tends to be more widespread in areas where hygiene levels are poor and where living in crowded conditions
          • Infection - bacteria invades type of white blood cell in lungs where they can lay dormant for years, when someone infected the immune system builds wall around bacteria in lungs forming a small hard lump known as tubercles
            • Infected tissue within dies and gaseous exchange surface is damaged so becomes difficult to breathe, if bacteria enters bloodstream they can spread to other parts of body
              • Many with TB are infected but don't show symptoms but if they become weakened (by other disease or malnutrition) the infection can become active and symptoms will show as they are able to pass on infection
          • Preventing and Treating - prevented by BCG vaccine and treated with antibiotics but there;s a big problem with antibiotic-resistant strains, improves living standards and hygiene can also help prevent TB
        • AIDS and HIV - Acquired  Immunodeficiency Syndrome is disease of immune system caused by Human Immunodeficiency Virus
          • Transmission - HIV is transmitted in 3 main ways: unprotected sex, infected bodily fluid (shared needles) and from mother to feuts
          • Infection -  HIV is made up of core containing genetic material (RNA) and some proteins (including reverse transcriptase enzyme needed for virus replication), outer coating of protein called capsid and extra outer layer called envelop made of membrane stoled from previous host cell
            • HIV infects leukocytes, can only reproduce inside cells of infected organism, doesn't have equipment to replicate on its own so uses host cell
            • 1. Virus attaches to receptor molecule on cell membrane of host cell
              • 2. Capsid released into cell where it uncoats and releases genetic material into cells cytoplasm
                • 3. Inside the cell the reverse transcriptase is used to make complimentary strand of DNA from viral RNA template
                  • 4. From this a double stranded DNA is made and inserted into human DNA
                    • 5. Host cell enzymes used to make viral proteins from viral DNA found within human DNA
                      • 6. VIral proteins are assembled into new viruses which bud from the cell and go on to infect other cells
            • HIV infection eventually leads to AIDS ; condition where immune system deteriorates and eventually fails due to loss of white blood cells, it makes sufferer more vulnerable to other infections
          • Preventing and Treating - no cure of vaccine for HIV, antiviral drugs can treat it as they work by inhibiting virus-specific enzymes like reverse transcriptase,, but treatment  can only slow down progression as you can't kill HIV with drugs so best way to control it is to reduce it's spread
            • This can be done by : wearing condoms, screening blood donor volunteers, not sharing hypodermic needles and taking antiviral drugs during pregnancy
        • Global Impact
          • Malaria, TB and HIV are common in sub-Saharan Africa and other developing countries
            • This is because : limited access to good healthcare limited health education to inform people of how to avoid infectious diseases, limited equipment to reduce spread of infection, overcrowded conditions
          • Prevalence of these in developing countries slows down social and economic development as the diseases increase death rater and reduce productivity while resulting in high healthcare costs, studying global distribution is important
            • Information can be used to find out where people most at risk, data collected can be used to predict where epidemics most likely, important for research, allows organisations to provide aid where most needed
      • Smoking and DIsease
        • Damage to Cardiovascular System - both carbon monoxide and nicotine can damage the cardiovascular system and increase the risk of atherosclerosis, coronary heart disease, and stroke
          • Atherosclerosis- hardening of arteries due to formation of fibrous proteins called athromas in arterial wall, these contain LDL which contain a mixture of protein and cholesterol
            • Formation of atheroma usually begins when damage occurs to lining of artery, allows LDL to enter and collect in wall and the build up of LDL triggers an immune response causing white blood cells to move into the area
              • Over time more white blood cells lipids and connective tissue build up and harden to form fibrous plaque at site of damage so the atheroma partially blocks the lumen of the artery and restricts blood flow
                • Cigarette smoke contains nicotine and carbon monoxide which cause increase in blood pressure which can cause damage to the arteries and lead to formation of more atheromas
          • Coronary Heart Disease (CHD) - where coronary arteries have lots of athromas in them restricting blood flow to heart, this reduces amount of oxygen an area of the heart gets and forces heart muscle to respire anaerobically causing angina or a heart attack
            • Carbon monoxide irreversibly combines with haemoglobin which reduces amount of oxygen transported in blood therefore reducing the amount available to tissues and the heart
            • Nicotine makes platelets sticky which increases the change of blood clots forming, if clotting happens in coronary arteries it could cause heart attack and presence of athromas increases blood clot formation
            • Treatment - using a stent : tube like structure that can be placed in obstructed arteries to increase the diameter of artery and increase blood flow meaning more oxygen can reach the heart so it can respire aerobically
          • Stroke  - rapid loss of brain function due to disruption of blood supply to brain, can be due to blood clot in artery leading to brain restricting amount of blood and oxygen that reaches the brain, nicotine increases risk as it increases risk of clots, carbon monoxide also increases risk as it reduces amount of oxygen available by combining to haemoglobin
        • Damage to Gas Exchange System - smoking can also damage gas exchange system increasing the risk of lung cancer, bronchitis and emphysema
          • Lung Cancer - cigarette smoke contains mant carcinogens that may cause mutations in DNA of lung cells which could lead to uncontrolled cell growth and formation of a malignant tumour
            • Tumours grow uncontrollably so block air flow to areas of the lungs, this decreases gas exchange leading to shortness of breath as body is struggling to take in enough oxygen, tumour uses lots of nutrients and energy to grow so causes weight loss
          • Chronic Bronchitis - long term inflammation of mucous membrane lining the bronchi, these are lined with goblet cells that produce mucus to trap microorganisms, also lined with cilia that beat to move mucus up towards throat to be removed
            • Tar in cigarette smoke damages cilia and causes goblet cells to produce more mucus which accumulates in lungs causing increased coughing to try and remove it, microorganisms multiply in mucus and cause lung infection that leads to inflammation which decreases gas exchange
            • This is a type of chronic obstructive pulmonary disease - a group of diseases that involve permanent air flow reduction (COPD)
          • Emphysema - chronic lung disease involving breakdown of alveoli, caused by smoking of long term exposure to air pollution and is also a type of COPD
            • As with chronic bronchitis tar causes a build up of mucus which leads to infection and inflammation of lungs, inflammation attracts phagocytes to the area which produce an enzyme that breaks down the protein elastin (elastic protein found in alveoli walls)
              • Loss of elastin means alveoli can't recoil to expel air as well which leads to destruction of the walls reducing the surface area of the alveoli
                • Loss of elastin and reduction of surface area reduces rate of gas exchange in alveoli resulting in less oxygen absorption in blood stream and transported around body, lack of oxygen reaching cells leaves sufferers feeling tired and weak
                  • Other symptoms include shortness of breath and wheezing, increased breathing rate as they try to increase amount of air reaching their lungs

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