B2- Keeping healthy

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Microorganisms causing disease

Pathogens: Microorganisms that cause disease and make us feel ill.

When microorganisms get into the body they reproduce quickly and cause symptoms of disease.


  • Release poisons or toxins.
  • Bacterial meningitis, tetanus, salmonella, foos poisoning and tuberculosis (TB).


  • Damage to cells as they spread.
  • Influenza, the common cold, measles and chickenpox.

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Microorganism reproduction


  • Bacteria reproduce by dividng in two, which is a type of asexual reproduction called binary fission.
  • Bacteria reproduce rapidly (exponential growth) in the ideal conditions of the human body.


  • Viruses need a host cell to reproduce. They enter the host cell and steal the cells mechanisms for making DNA and proteins and making copies of themselves.
  • The copies of the virus are released in very large numbers from the infected cell and go and infect other cells and/or other people.


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The immune system

The bodys external defences: Skin, saliva and tears and stomach acid.

The bodys internal defence is the immune system.

The immune system uses white blood cells to defend the body. White blood cells:

  • Are made in bone marrow.
  • Are found in several types: Some engulf and digest microorganisms, while others produce antibodies, which recognise and destroy invading microorganisms.


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The immune system

Pathogens have chemicals on their surface that antibodies recognise as being foreign. These are called antigens.

Different white blood cells carry different types of antibody on their surface. An antibody is specific to one antigen.

The antibody corresponding to an antigen locks onto it:

  1. The white blood cell divides to produce many copies.
  2. Each white blood cell produces many antibody molecules that lock onto invading cells.

Different types of antibody:

  • Destroy the invading microorganism.
  • Enable the white blood cells to recognise the microorganism as being foreign.
  • Cause the microorganism to clump together, meaning it is easier for white blood cells to engulf them.
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The immune system

After the infection clears up memory cells remain in the blood stream. These can produce large numbers of antibodies very quickly if the microoganism enters the body again.

At this point the person is said to be immune to the particular pathogen.


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White blood cells make antibodies against chemicals on the surface of pathogens. These chemicals are called antigens.

Memory cells left in the body can produuce antibodies very quickly if they meet the living disease-causing microorganism.

A vaccine contains a safe form of the microorganism that causes a diseaseso that you don't become ill after receiving it.

In the blood stream the immune system attacks the microorgaism in the vaccine.


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Vaccination programmes protect children against diseases that are preventable.

Babies and children undergo a course of vaccinations in their first year or so.

Some pathogens do not change over time, so the vaccination can be used against these year arfter year.

Other pathogens such as the influenza virus change rapidly so new vaccines must be developed.

An epidemic occurs if a disease spreads rapidly through a population.

To avoid an epidemic it is necessary to vaccinate a high percentage of the population- this leads to 'herd immunity'.

Widespread immunity has eradicated smallpox from the world. It has also reduced childhood diseases such as measles, mumps and rubella.

The longer term aim is to eradicate certain diseases altogether.

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Making vaccinations safe

Scientists test vaccinations to check for side effects.

Side effects can be more severe in some people than in others because of genetic variation.

No type of medical treatment can be completely rick free (but often people think the risk is higher than it is).

Vaccinations are extremely safe and millions have benefitted from them.

Occasionally a child may develop a minor adverse reaction (e.g. hay fever). In very rare cases, the reaction can be more serious. Any adverse reactions are recorded and followed up.

Risks of a vaccination must be considered against the benefits. Any reaction generating an unusual number of adverse reactions will be quickly withdrawn.

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Reducing infections

Antimicrobials: A group of subatances that are used to kill microorganisms or slow their growth. They are effective against bacteria, viruses and fungi.

Antibiotics: A type of antimicrobial which are effective against effective against bacteria but not against viruses. They allow doctors to treat illnesses caused by bateria such as tuberculosis.

Studies show that some microorganisms are developing resistance to these antimicrobials because of their wide use:

  • Resistance to antimicrobials means that some strains of bacterial infections are now difficult to control.
  • Antimicrobial-resistant microbes can be a problem in places where antmicrobials are used often e.g. hospitals.
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Antimicrobials are chemicals that prevent the growth of microorganisms so provide protection against disease. They include:

  • Antibiotics against bacteria; antivirals against viruses; antifungals against fungi.
  • Many cleaning products, along with antiseptics and disinfectants.

Over a period of time bacteria and fungi can grow resistant to antimicrobials. In a population of microorganisms, some may be resistant to the antimicrobial. These will survive the antimicrobial and will pass on the resistance. The resistance spreads through the population of microorganisms.

Resistant microorganisms are sometimes called 'superbugs'.


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The overuse of certain antibiotics has led to some microorganisms being resistant to them. For this reason a course of antibiotics should be:

  • Prescribed only for serious infections, when they are really needed.
  • Completed, so that the bacteria causing the infection are killed completely.

Random mutations in the genes, give some bacteria resistance to the antimicrobials.

Because of the rapid production rate of bacteria, antimicrobial-resistant genes spread through the population.

Antiobiotic resistance has led to some strains of bacteria that are very difficult to eradicate. These iclude MRSA, which is a problem in many hospitals.


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Trialling new treatments

New medicines, vaccines and other treatments are tested very carefully before being made available to the general public.

Early stages of testing involve human cells grown in a lab and animals.

If the drug seems to be effective and safe, it is tested on human cells in clinical trials. These are carried out on healthy volunteers (to check for safety) and on people with the illness (to test for safety and effectiveness).

When drug trials are carried out, one group is given the new drug being trialled. The results are compared with those of the control group.

One type of control group recieves the existing treatment; another type of control group recieves a placebo- a tablet or liquid made to look like the drug, but without the active ingredient.

One ethical issue of drug tests is that it must not disadvantage the patient. If evidence from the trial suggests the new drug is effective it is offered straight away to the patients recieving the placebo.


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Drug trialling

'Open-label' : both patients and researchers know what drug is being tested.

'Blind' Study: the patient doent know what drug they are recieving but the researcher does.

'Double blind': Neither patient nor researcher know what is being tested.

Some trials investigate the effects of the drug over a long period of time. Because:

  1. Side effects may appear or increase over time.
  2. The drug may become less effective.


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Heart and circulatory system

Circulatory system: Heart, blood vessels and blood.

The blood carries nutrients and oxygen to the bodies cells and removes and carries waste products from the cells.

Blood is pumped around the body in blood vessels by the heart.

The heart is a 'double pump':

  1. One half pumps oxygenated blood from the lungs to the body.
  2. The other half pumps deoxygenated blood from the body to the lungs.

At the lungs deoxygenated blood absorbs oxygen and gets rid of carbon dioxide.


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Blood vessels

The three types of blood vessels are: arteries, capilleries and veins.

Arteries: Away from the heart under high pressure. Walls are very thick, elastic and muscular to withstand the pressure.

Capillaries: Link arteries and veins. Walls are one cell thick to allow the transfer of substances to and from cells.

Veins: Collect blood and return it to the heart. Walls contain elastic, muscular tissue, but are thinner than those of arteries. The blood is under low pressure and veins have valves to prevent the backflow of blood.

Heart muscle has its own blood supply. The coronary arteries run over the surface of the heart. They provide the heart with the nutrients and oxygen it needs to contract and remove waste products.

The coronary arteries can become blocked by fatty deposits. This will prevent the heart from receiving the oxygen it needs leading to a heart attack.

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Reducing the risk of heart attack

Coronary heart disease is caused by the build up of fatty substances in the arteries.

Lifestyle factors that increase a persons rick of CHD:

  1. Smoking
  2. Poor diet (high in saturated fat)
  3. Misuse of drugs
  4. Stress

There is a correlation between these factors and coronary heart disease.

Regular exercise helps to prevent CHD because it strengthens the heart muscle, providing a healthy body weight and reducing strength.

A healthy diet; low in saturated fat lower the blood cholesterol and reduces the risk of heart disease.

Genetic factors contribute to the risk.

Rates of CHD are higher in industrialised countries such as the UK and USA, than less industrialised e.g. India and China.

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Heart rate

Heart rate is measured by recording pulse rate. This is the number of pulses as blood passes through an artery close to the skin.

Pulse rate is measured in beats per minute (BPM).

Resting heart rate: heart rate when a person is relaxed. A resting heart rate of 70-100bpm is normal for teenagers, 50-70 is a good indication of a good level of fitness.

The misuse of drugs such as nicotine, alcohol and ecstasy has a negative effect on health, including heart rate, and increases the risk of heart disease and heart attack.


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Blood pressure

Blood pressure measurements record the pressure of blood on the walls of an artery.

People with consistantly 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 also puts strain on the heart.


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Blood needs to be under pressure to reach every cell in the body.

Blood pressure is an important indicator of health.

  • High blood pressure increases the chance of strokes and heart disease.
  • Low blood pressure can cause dizziness and fainting.


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Epidemiological studies

Studies of the occurance of heart disease using large numbers of individuals called epidemiological studies.

They have been carried out on the link between lifestyle factors and heart disease.

Studies are carried out:

  • On samples of individuals who are matched on as many factors as possible and differ in only the factor being investigated.
  • On individuals chosen at random.
  • That investigate whether the genes carried by individuals affect their risk of suffering from particular problems.


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Homeostasis: The maintenance of a constant environment.

Temperature, pH and levels of sugar, water and salt must be kept at values within a very narrow range for the body to function.

Homeostasis involves communication by the nervous and hormonal systems.

Response to change is by these 'automatic' control systems throughout the body.

The systems involved in homeostasis are in three parts:

  1. Recepters: detect change in the environment.
  2. Processing centres: receive information and determine how the body will respond.
  3. Effectors: produce a responce.
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Water balance

Water is taken in by drinking and eating and it's produced by respiration.

Water is lost in urine and faeces and when we sweat and breath out.

The water content of our bodies must be maintained to keep the bodies cells bathed in blood plasma. So, the concentration of water in our cells must be kept constant.

If the blood plasma is too concentrated, the cells will lose water.

If the blood plasma is too dilute, the cells will absorb water and bust.


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The kidneys

Concentration of blood plasma is affected by external temperature, exercise level and intake of fluids and salt.

The kidneys respond to changes in the blood plasma by changing the concentration of urine that is excreted from the body.

Some recreational drugs affect the water balance of the body:

  • Alcohol causes the kidneys to produce a large volume of dilute urineand the body becomes dehydrated.
  • Ecstasy causes the kidneys to produce very large volumes of concentrated urine. The bodies cells swell with water.

The kidneys help to balance levels of water, urea, salts and other chemicals in the blood.

Anti-diuretic hormone (ADH) is released by the pituitary gland in response to changes in the concentration of blood plasma. The secretion of ADH is controlled by negative feedback.

ADH acts upon the kidneys to reduce the amount of water lost in the urine.

Alcohol supresses the release of ADH, so less water is absorbed by the kidneys.

Ecstasy increases ADH production, so more water is reabsorbed by the kidneys.

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