BIOLOGY UNIT 1
1.Causes of Disease
1.1_Pathogens
- Pathogens are microorganisms.
WHAT IS DISEASE?
- Disease is a description of certain symptoms, not a single ‘thing’.
- Could be physical, mental, or both.
- Disease suggests malfunction in the body or mind resulting in adverse effect on health.
MICROORGANISMS AS PATHOGENS
- Gain entry to host
- Colonise tissues of host
- Resist defences of host
- Cause damage to host tissues
- Pathogens include bacteria, viruses and fungi.
- If a pathogen colonises a hosts tissues, infection is the result.
- Disease occurs when infection leads to recognisable symptoms in host.
- When a pathogen is transferred from one individual to another, this is called transmission.
HOW DO MICROORGANISMS GET INTO THE BODY?
· Pathogens get into the body by penetrating one of the organisms interfaces with environment.
· One interface is the skin when it is broken. (When unbroken the skin is a thick, continuous layer so is an effective barrier to infection.)
· Some interfaces have evolved to allow exchange of material so linings here are thin, moist, have a large surface area and are well supplied with blood vessels. This makes for easy entry for molecules, including pathogens.
· Examples include the gas exchange system – Many pathogens enter here, including ones that cause influenza, TB and bronchitis.
Digestive system – Food and water can carry pathogens into stomach and intestines via mouth, pathogens such as cholera, typhoid and dysentery enter here.
· To try and prevent entry, body has natural defences:
-Mucus layer covers exchange surfaces and forms thick sticky barrier that’s difficult to penetrate.
-Enzymes break down pathogens.
-Stomach acid kills microorganisms.
HOW DO PATHOGENS CAUSE DISEASE?
Two main ways:
· Damaging host tissues – sometimes just the number of them by preventing tissues functioning properly. Viruses inhibit synthesis of DNA, RNA and proteins. Many pathogens break down membranes of host cells.
· Producing toxins – Most bacterial pathogens. Cholera bacterium produces toxin that leads to excessive water loss from lining of intestines.
· Some diseases like malaria have just one cause, while others like heart disease have a number of causes.
· How quickly a pathogen causes damage is related to how quickly it divides.
· Pathogens like those causing gastroenteritis, deivide every 30mins so symptoms become apparent within 24 hours. Gastroenteritis pathogen only causes damage in large numbers.
· Pathogens such as typhoid bacterium cause harm in small numbers.
1.2_Data and Disease
ANALYSING AND INTERPRETING DATA ON DISEASE
- Epidemiology is the study of the incidence and pattern of disease with a view to finding means of preventing and controlling it.
- Epidemiologists collect data and look for a pattern or relationship between the diseases and various factors in lives of people who have them.
CORRELATIONS AND CAUSAL RELATIONSHIPS
CORRELATIONS DO NOT MEAN CAUSATIONS!!!!!
- A correlation occurs when a change in one variable is reflected by a change in the other.
- This does not however mean that we can say that one change CAUSES the other.
1.3_Lifestyle and health
WHAT IS RISK?
A MEASURE OF THE PROBABILITY THAT DAMAGE TO HEALTH WILL OCCUR AS A RESULT OF A GIVEN HAZARD.
Concept of risk has 2 elements:
-Probability that hazardous event will occur.
-Consequences of that hazardous event.
- These factors affect how we perceive risk, e.g. risk of catching a cold is high, but consequences are minor so we don’t tend to worry much.
- Consequences of being struck by lightening are severe, but unlikely to happen so again, we don’t worry too much.
- When both factors are high = worry.
Risk is measured in %.
Health risks need timescale – telling someone risk of dying is 100% is meaningless, saying their risk of dying in the next month is 100%, has a totally different meaning.
Risk is often relative – Risk is measured by comparing likelihood of harm occurring in those exposed to a hazard with those not exposed to it. i.e. Smokers are 15x more likely to develop lung cancer.
Misleading statistics – reports in media may be misleading as they focus on a single figure, suggesting this figure applies to everyone.
LIFESTYLE CHOICES AND CANCER
Can’t do anything about our genes, or age, but lifestyle can expose us to environmental and carcinogenic factors.
*Smoking – nicotine is a carcinogen, and can affect passive smokers too.
*Diet – What we eat & drink affects risk of contracting cancer.
*Obesity – Being overweight increases risk.
*Physical activity – People who take regular excersise have lower risk from some cancers than those who do not exercise.
*Sunlight – Great exposure to UV rays increase risk of developing skin cancer.
RISK FACTORS AND CORONARY HEART DISEASE
· CHD is largest cause of death in UK
· When combined, 4/5 of the risk factors produce a disproportionately greater risk.
LIFESTYLE CHOICES AND CHD
Can’t control genes age or sex.
But can control:
· Smoking – Smokers between 2 and 6 times more likely to suffer from CHD.
· High Blood Pressure – Excessive prolonged stress, certain diets and lack of exercise increase blood pressure and hence risk of CHD.
· Blood cholesterol levels – Can be kept lower by includning fewer saturated fats and fatty acids in diet.
· Obesity - BMI of over 25 = increased risk.
· Diet – High levels of salt raise blood pressure while high levels of saturated fatty acids increase blood cholesterol concentration.
· Physical exercise – Aerobic exercise can lower blood pressure and blood cholesterol as well as helping to avoid obesity.
Infection- invasion and multiplication of microorganisms in body tissues
Disease- A disorder of structure or function in a human, animal, or plant, that produces specific signs or symptoms
Transmission- The transfer of a pathogen from one individual to another.
Interface- A point where two systems, subjects, organizations, etc., meet and interact.
RNA- ribonucleic acid; any of a group of nucleic acids, present in all living cells, that play an essential role in the synthesis of proteins.
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