SB5 Health, Disease and the Development of Medicines

SB5a Health and Disease

  • WHO says health is a state of 'complete physical, social and mental well-being'. 
  • Physical well-being: free from disease, eating and sleeping well and limiting intake of harmful substances i.e. drugs.
  • Social well-being: how well you get on with other people and how your surroundings affect you.
  • Mental well-being: how you feel about yourself. 
  • Non-communicable - diseases that are not passed from one person to another e.g. cystic fibrosis. 
  • Communicable - diseases caused by pathogens (microorganisms that cause diseases) and can be passed from an infected person to other people. 
  • Disease may be correlated due to: 
  • One disease damages the immune system, making it easier for pathogens to cause disease. 
  • Disease damages the body's natural barriers and defences, allowing pathogens to get into the body more easily. 
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SB5b Non-communicable diseases

  • Malnutrition - getting too little or too much of particular nutrients.
  • Protein deficiency - kwashiorkor, enlarged belly and failure to grow. 
  • Vitamin C deficiency - scurvy, swelling and bleeding gums
  • Vitamin D/Calcium deficiency - rickets or osteomalacia, soft bones and curved leg bones.
  • Iron deficiency - anaemia, red blood cells smaller than normal and numbers reduced.
  • Ethanol, found in alcohol, is broken down by liver and large amount can cause liver disease, leading to cirrhosis. 
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SB5c Cardiovascular Disease

  • Obesity - large amounts of fat are formed under the skin and organs such as heart. 
  • Cardiovascular disease - result of the circulatory system functioning poorly. One sign is high blood pressure, which can lead to a heart attack.
  • Body mass index - mass ÷ height² 
  • BMI is used to predict the amount of fat, an adult who has a BMI of 30 is obese. 
  • Dividing waist-to-hip ratio gives a better method of measuring abdominal fat as BMI dosn't distinguish between muscle and fat. 
  • Tobacco contains harmful substances that can damage lungs. Some substances are absorbed from lungs into the blood and transported around the body. These can damage blood vessels, increase blood presure and increase the risk of blood clots forming in blood vessels (fat builds up in artery wall making artery narrower).
  • A narrowed blood vessel can be widened by inserting a small mesh tube (stent) to hold it open. 
  • Blocked arteries can be bypassed so that the heart tissue os supplied with oxygen and nutrients.
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SB5d Pathogens

  • Cholera - severe diarrhoea.
  • Tuberculosis (TB) - bacterium infects and damages lungs, resulting in bloody mucus after coughing.
  • 4 main types - Viruses (HIV/AIDS), Bacteria (Salmonella), Fungi (Athlete's foot) and Protists (Malaria).
  • Viruses - don't have cellular structure and multiply by infecting a cell and taking over the cell's DNA-copying processes to make new viruses. HIV attacks and destroys white blood cells in the immune system, which often develops to AIDS because the immune system cannot protect them from secondary infections. 
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SB5e Spreading Pathogens

  • Infections, such as colds, can cause a person to sneeze and send droplets containing pathogens into the air. In air, it can survive for about a day.
  • Fungi, e.g. chlara ash dieback, can also spread as tiny tough spores. 
  • Water - e.g. cholera, are normally rare in developed countries as water is treated to kill pathogens. 
  • Unhygienic food - undercooked food can cause bacterial diseases e.g. E.coli, which is a cause of food poisoning. 
  • Direct contact - i.e. shaking hands.
  • Vector - any organism that can spread a disease. 
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SB5f Virus Life Cycles

  • Capsid - viruses that contain one or more strands of genetic material surrounded by a protein coat. 
  • Viruses are unable to replicate, so they had to enter a living cell and take over cell's processes for making new DNA and proteins. They don't divide and reproduce like cells, but complete the lytic pathway.
  • Lytic pathway - Virus attaches to cell and injects genetic material. Viral material forms a cycle and new viral genetic material/protein are produced and assembled. This causes host cell to burst called the lysis. 
  • Lysogenic cycle - the DNA is only replicated. Viral genetic material inserts itself into the bacterial chromosome. Bacterium reproduces normally, replicating viral genetic material at each cell division. Cell and viral genetic material may reproduce many times, or/and occasionally, viral genetic material separates from the bacterial chromosome, causing a lytic cycle. 
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SB5g Plant Defences

  • Cuticle - (physical barrier) waxy layer on the outside of leaves and stems, stopping pathogens from getting into the cells beneath. Woody plants also have bark. 
  • If pathogens get through the barriers, they must penetrate cell walls to get inside the cells. Some release enzymes to soften cell walls. 
  • Physical barriers are not good protection against herbivores, instead plants use chemical barriers, such as poision or insect repellents. 
  • Many medicines that we now use were developed from substances that plants use to protect themselves. 
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SB5h Plant Diseases

  • Plants show signs of stress whenever conditions are not good enough to grow. Scientist try to identify the cause so the farmer can treat the crop correctly and prevent loss of yield.
  • Careful observation - looking for visible symptons, i.e. changes with colour and bloches of leaves. 
  • Distribution analysis - looking at where the damaged plants occur. Flooding will create similar symptons in all the plants. Disease that are airborne will affect plants over a wide area, but most obviously where the wind first reaches the crop. 
  • Diagnostics - sending samples to a lab for testing. The testing will help the lab to be more certain of the cause of the problem.
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SB5i Physical and Chemical Barriers

  • Skin - physcial barrier, pathogens can only cross the barier if they pierce the skin. It contains glands that secrete substances onto skin surface, lysozyme.
  • Lysozyme(chemical defence) An enzyme that breaks down bacteria cell walls, secreted in tears, saliva and mucus.
  • Mucus - it helps to protect the thinner surfaces of the body. It is a sticky secretion produced by cells lining the many openings, such as the mouth and nose, that pathogens could use to enter body. Pathogens get stuck in the mucus.
  • Ciliated cells - specialised to move substances such as mucus either out of the body or into the digestive system.
  • Hydrochloric acid - reduces the pH of the stomach contents to 2, and kills many pathogens because of the acidity. 
  • STIs - pathogens spread by contact with sexual fluids, and can be reduced by using a artificial barrier, condom, during sexual intercourse. 
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SB5j The Immune System

  • If pathogens pass the physical and chemical barriers, the immune system attacks the pathogens.
  • All cells and virus particles have molecules on their outer surfaces called antigens, which are unique. A white blood cell, lymphoctye with an antibody that fits the antigen attactes to pathogen, stopping it from working.The lymphocyte is activated and divides rapidly to produce identical lympocytes. Some of the lymphocytes secrete large amounts of antibodies, the antibodies stick to the antigens and destroy the pathogens. Other lymphocytes remain in the blood as memory lymphocytes, ready to respond if it comes back.
  • Memory lymphocytes cause a much faster secondary response. This means that you are immue to that pathogen. 
  • Immunity can be triggered artificially by using a vaccine. The vaccine contains weak or unactive pathogens. The vaccine may be injected into the body and usually causes little reaction. 
  • Some may be illergic, however they are still protected as 95% of other children are immune , because their chance of coming into contact with an infected person will be very low - herd immunity.
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SB5k Antibiotics

  • Antibiotics - substances that kill or inhibit their cell processes, which stops them growing or reproducing. Antibiotics don't have this effect on human cells, making them useful for attacking bacterial infections.
  • Problems - bacteria are becoming resistant to the antibiotic, new antibiotics must be created.

Development of new medicine -

  • Pre-clinical stage (testing new medicine on cells/tissue), this stage shows if medicine has a required effect and any side effects.
  • Clinical trial (testing on animals), shows if it works in a whole body (without risk to humans) and if that is successful a clinical trial on humans, to check if it's safe.
  • Medicine is then used in large clincial trail on many people who have the disease. This helps to work out the dose. 
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SB5l Monoclonal Antibodies

  • Pregnancy test - detect hormone in tiny amounts that is produced when she is pregnant, so must be sensitive. This is achieved by using antibodies specially made to match hormone.
  • Monoclonal antibodies - large amounts of identical antibodies which can be made to stick to cancer cells or pathogens. It cannot be made in large amounts using normal lymphocytes, as although lymphocytes divide rapidly, once it has started producing antibodies it cannot divide any more. 
  • Hybridoma cells are made, fusing lymphocyte that produces the antibodies with a cancer cell. Stage 1: antigen/human hormone is injected into a mouse, mouse produces lymphocytes that make antibodies against human hormone. Stage 2: lymphocyte from mouse and cancer cell fuses. Stage 3: The hybridoma cell can both divide and make antibodies against the human hormone. These are monoclonal antibodies.
  • Monoclonal antibodies can be used to medical diognosis, by making the antibodies radioactive. When antibodies stick to cancer cells, radioactivity can be detected and so cancer cells can be found.
  • Chemotherapy/Radiotherapy can often damage healthy cells. Cancer drugs can be carried on monoclonal antibodies and this reduces the amount of drug needed to kill the cancer cells and reduces risk of damaging healthy cells. 
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