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Causes of disease

  • micro-organisms that cause disease and make us feel ill are called pathogens, these include bacteria and virus
  • when micro-organisms get into the body they reproduce quickly and cause symptoms of disease
  • bacteria reproduce by dividing into two, which is a type of asexual reproduction called binary fission
  • bacteria reproduce rapidly in the conditions of the human body
  • viruses need a host cell to reproduce, they enter the host cell and hijack the cells mechanisms for making DNA and proteins and make copies of themselves
  • the copies of the virus are released in large numbers from the infected cell and go onto infect other cells or other people
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The Defense System

  • bodys external defences; skin, saliva, and tears
  • bodys internal defences; the immune system
  • the immune system uses white blood cells to defend the body, white blood cells are made in the bone marrow and are found in several types. some engulf and digest invading micro organisms whereas some produce antibodies to recognise and destroy the micro organisms
  • pathogens have chemicals on their surface that antibodies recognise as being foreign, these are called antigens
  • an antibody is specific to one antigen
  • the antibody corresponding to an antigen locks onto it, the white blood cell then divides to produce many copies, each white blood cell makes many antibody molecules that lock onto the invading cells
  • another type of antibody destroys the invading micro organism and enables white blood cells to recognise the micro organisms as being foreign, it causes the micro organism to clump together meaning it is easier to engulf by the white blood cells
  • once the infection clears up, memory cells remain in the bloodstream which can fight off the infection quicker if it enters the body again, therefore the person is immune to the pathogen
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  • White blood cells make antibodies against chemicals on the surface of the pathogens, called antigens
  • a vaccine contains a safe form of the micro organism that causes a disease so that you dont feel ill after recieving it
  • vaccination programmes are to protect children against preventable diseases
  • some pathogens change overtime, e.g. flu, so new vaccines must be developed
  • an epidemic occurs if a disease spreads rapidly through a population
  • herd immunity is to prevent an epidemic, it is the process of vaccinating a high amount of a population
  • side effects in some people can be more severe than in others due to genetic variation
  • they are never risk free but the benefits outweigh the drawbacks


  • a group of substances that are used to kill microorganisms or inhibit their growth
  • they are effective against bacteria, virus, and fungi


  • only against bacteria but not virus
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  • over a period of time, bacteria and fungi can develop resistance to antimicrobials
  • in a population of micro organisms, some may be resistant to the antimicrobial, they will survive and pass on resistance
  • resistant microorganisms are sometimes called superbugs
  • reasons for resistance- overuse of antimicrobials, unfinished courses, and mutations
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Clinical Trials

  • early stages of testing- computers, human cells in a lab, animal cells
  • if the drug seems effective and safe it is tested on humans in clinical trials
  • these are carried out on healthy people to check for safety, and people with the illness to check for results
  • when drug trials are carried out, one group is given the new drug, one group is given a placebo
  • placebo- a tablet or liquid made to look like a drug but without the active ingredient
  • open-label trial- both researchers and patient knows which drug is taken
  • blind study trial- patient doesnt know which drug is taken but researcher does
  • double blind study trial- neither know which drug is taken
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The Heart and Circulatory System

  • consists of the heart, blood vessels, and blood
  • blood carries nutrients and oxygen to the bodys cells and removes waste products from the cells
  • blood is pumped around the body in vessels by the heart
  • the heart is a double pump, one half is pumping oxygenated blood from the lungs to the body, the other half is carrying deoxygenated blood from the body to the lungs
  • at the lungs, deoxygenated blood absorbs oxygen and gers rid of carbon dioxide

Arteries- transport blood away from heart under high pressure. walls are thick and muscular to withstand the pressure

Capillaries- link arteries and veins, walls are once cell thick to allow the transfer of substances to and from cells

Veins- collect blood and return it to the heart, walls contain muscular tissue but are thinner than arteries, blood is under low pressure, have valves to prevent backflow of blood

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Heart Disease

  • Coronary Heart Disease is caused by a build up of fatty substances in the arteries
  • the main lifestyle factors that increase the risk are smoking, bad diet, misuse of drugs, alcohol, and stress
  • there is a correlation between these factors and heart disease
  • a diet low in saturated fat lowers blood cholesterol and reduces the risks
  • genetic factors contribute to the risks

heart rate is measured by pulse rate, which is measured in beats per minute

a resting heart rate of 50-70 bpm is healthy for an adult

people with consistently high blood pressure have an increased risk of heart disease, high blood pressure damages the walls of the arteries and makes them more likely to develop fatty deposits and get narrower. it puts strain on the heart

high blood pressure- increased chance of heart attack or stroke

low blood pressure- can cause dizziness and fainting

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Epidemiological studies

  • studies of the occurence of diseases using a large number of individuals
  • can show a link between lifestyle factors and disease
  • carried out on samples of individuals who are matched on as many factors as possible and differ only in the factor being investigated, or individuals chosen at random
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A Constant Internal Environment

  • Homeostasis- keeping a constant internal environment
  • temperature, pH levels, sugar, water, and salt levels must be kept within a certain value for the body to function
  • the system includes- RECEPTORS; detects change in the environment, PROCESSING CENTRE;recieves information and determines how the body will respond EFFECTORS; produce a response
  • water is taken in by drinking, eating, and respiration. it is lost in urine, faeces, sweat, and respiration
  • if the blood plasma is concentrated the cells will lose water, if the blood plasma is diluted, the cells will absorb water and burst
  • the kidneys respond to changes in blood plasma by changing the concentration of urine that is excreted from the body
  • ADH is released by the pituitary gland detected by the hypothalamus. if there is a high amount of water intake, there is a low amount of ADH released, so the kidneys do not absorb the water. therefore you urinate more with low concentration urine.
  • if there is a low amount of water intake, there is a higher amount of ADH released; so the kidneys reabsorb the water, therefore you urinate less with a high concentration urine.
  • alcohol supresses the release of ADH so you urinate more, and become dehydrated
  • ecstasy increases ADH production so more water is reabsorbed by the kidneys, however you may still drink lots and eventually drown your brain
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