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BIOLOGY UNIT 3: HEALTH AND DISEASE
INTRODUCTION
The World Health Organization (WHO) defines health as "a state of complete physical,
mental, and social well-being and not merely the absence of disease”. This means that health is
related to many aspects such as personal satisfaction, emotional wellness, social life… not only
physical health.
A disease is an abnormal condition that affects part or all of an organism and prevents the
body or mind from working normally. For example, when somebody is depressed or has an infection
or a wound, his or her body doesn’t work normally.
DETERMINANTS OF HEALTH
Our health depends on personal lifestyle (this is normally the most important factor), the
environment, health care services and genetic factors (this is normally the least important factor).
1. PERSONAL LIFESTYLE
A lifestyle choice is a personal and conscious decision to behave in a way that may increase
or decrease the risk of injury or disease. Lifestyle choices that benefit your health are varied and
include a balanced diet, performing regular exercise, not to use drugs such as tobacco or alcohol and
to practice safe sex.
-DIET: An important way to maintain your personal health is to have a healthy diet that
provides the nutrients that your body needs. A good balanced diet includes mainly natural (not
processed such as refined) plant-based foods (olive oil, vegetables, legumes, fruits and whole cereal
grains) and small amounts of animal products (better more fish than meat). It is important that the
food is natural (avoid processed food) and not to eat too much (only the amounts you need, don’t eat
when you are not hungry). It’s also important to eat raw food everyday because the heat produced
from cooking destroys vitamins and other nutrients.
In developed countries some common nutritional imbalances are an excess of sugars, animal
proteins and animal lipids, salt, omega-6 fatty acids and a deficiency of plant-based food, omega-3 fatty
acids and fibre. Most processed foods contribute to all these nutritional imbalances. These nutritional
imbalances are a major contributor to the chronic diseases that are so common in developed countries
such as heart disease, developing some types of cancer, obesity and diabetes.
Exercise: Why do processed foods contribute to nutritional imbalances?
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-EXERCISE: Physical exercise enhances or maintains physical fitness and overall health and
wellness. It prevents the most common diseases in developed countries (cardiovascular disease,
cancer and chronic respiratory diseases), for example: physical inactivity doubles the risk of heart disease. It
helps maintain weight (decreases risk of obesity), contributes to achieve adequate levels of blood
cholesterol, blood glucose (decreases risk of obesity) and blood pressure (decreases risk of
hypertension), and improves mental status (reduces the risk of depression and anxiety, improves
mood and promotes a feeling of well-being).
-DRUGS: all drugs are unhealthy, we will see the most common ones: alcohol and tobacco:
Alcohol: can cause traffic accidents and in the long term, diseases such as various cancers,
depression…
Tobacco: The consumption of tobacco is the largest preventable cause of death in developed
countries! In developed countries, the three leading causes of death from highest to lowest by number
of deaths: cardiovascular disease, cancer and chronic respiratory diseases. Tobacco influences these
three greatly:
- Cardiovascular disease: Smokers are at three times more risk of cardiovascular
disease than the rest of the population.
- Cancer: A third of all cancers are caused by tobacco! (Smoking is a major risk factor for
cancers of the mouth, larynx, esophagus, lung, stomach, pancreas, kidney, bladder, and cervix. In Spain, the
cancer that causes more deaths in men is lung cancer and in women is the second (after breast cancer), but with
the rise in recent decades of women smokers is estimated that by 2020 lung cancer will be also the cancer that
causes more deaths in women. About 90% of patients with lung cancer are smokers.
- Chronic respiratory diseases: Smoking is also the leading cause of chronic lung
diseases. In fact; a smoker is 10 times more likely to die from a chronic lung disease than a
nonsmoker. In general, smokers die 10-12 years earlier than nonsmokers! Cigarette smoke
contains more than 4,000 chemicals, including 63 carcinogens and trace amounts of poisons such as cyanide,
arsenic and formaldehyde. After the smoke passes through the mouth, lungs retain 70-90% of the compounds
that are inhaled. Photo: Non smoking lung pink (left) and smoking lung black (right).
-SEXUAL HEALTH:
You should not risk having sex without protection (condoms) to prevent sexually transmitted
diseases such as AIDS, syphilis, gonorrhoea...
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2. ENVIRONMENT
Among the environmental factors that determine our health are pollutants and social and
labour relations.
- Social and labour relations: Social and labour relations that most affect our health are
stress, overload of activities, exhaustion and labour relations as problems with the boss or colleagues.
- Pollutants: The pollutants that affect our health can be divided into physical, chemical and
biological:
- Physical: include noise, radioactivity and ultraviolet radiation. Noise can cause nervousness,
insomnia, stress, deafness ... Ultraviolet radiation and radioactivity can cause cancer.
- Chemicals: include toxic gases produced by burning fossil fuels (oil, coal and natural gas)
used for transport, industry and electricity production. These gases affect the respiratory system.
They also include toxic chemical substances added to food (pesticides, some food additives…) and
many toxic chemical substances added to industrial products such as clothes, cosmetics,
electronics… can also damage your health.
- Biological: are all kinds of pathogens or parasites that can cause us diseases, mainly
microorganisms (viruses, bacteria, fungi and protozoa).
3. GENETIC FACTORS
Even though most diseases have a hereditary component that predisposes the individual to
suffer them, what more increases the probability of suffering them are the personal lifestyle and
environment choices. For example: If your parents are hypertensive or diabetic, your probability of
having these diseases in the future is higher but you will rarely suffer them if you live a healthy life
(healthy diet, exercise regularly, not to smoke…) and you live in a healthy environment (no pollution
in the air or water…).
4. HEALTH CARE
A country’s health system plays a basic role in maintaining the health of its population. The
availability of medical professionals and medicines such as antibiotics (kill bacteria) and vaccines
(contains the deactivated microorganism, when we are exposed to this microorganism through
vaccination, our body learns how to fight against it) vary greatly between developed and developing
countries. This large difference in availability of health care is what determines the difference among
the leading causes of death in developed and developing countries, therefore, while in developed
countries the main causes of death are non-infectious diseases (cardiovascular diseases, cancer and
chronic respiratory diseases, in this order), in developing countries the main causes of death are
infectious diseases such as diarrhoea, measles, influenza, malaria ... with vaccines and medications
these diseases rarely cause death.
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HEALTHY HABITS
Exercise: after reading the four determinants of health, what would you recommend to be
healthier?
TYPE OF ILLNESSES
According to their origin, illnesses are classified as infectious diseases and non-infectious
diseases.
1. INFECTIOUS DISEASES
Infectious diseases are the main cause of death in developing countries. They are produced by
pathogenic agents, mainly microorganisms such as viruses, bacteria and protozoa.
The most known examples of diseases caused by viruses are: AIDS (SIDA), the common cold
(resfriado común) and influenza or flu (gripe). AIDS is a serious illness that attacks the defence system, the
common cold causes slight discomfort, an increase in nasal secretions, congestion and sneezing. It does not generally
cause a fever and influenza sometimes has similar symptoms to the common cold, but flu is a more serious illness than
the cold, flu causes greater discomfort, pain in the joints and it generally causes a fever.
Some diseases caused by bacteria are salmonella, tetanus and tuberculosis. Salmonella causes
serious digestive disorders and a high fever, tetanus causes muscular rigidity and difficulty in movement and tuberculosis
attacks mainly the lungs causing coughing.
The most known disease caused by protozoa is malaria, a very common tropical disease, the
protozoa is transmitted by the bite of a tropical mosquito.
The pathogenic agents that produce infectious diseases can be transmitted in different ways
such as drinking contaminated water or eating contaminated food or transmitted through the saliva or
mucus expelled when coughing or sneezing.
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2. NON-INFECTIOUS DISEASES
Non-infectious diseases are the main cause of death in developed countries. They are not
produced by pathogenic agents and they are not transmitted (except for genetic illnesses). The most
common non-infectious diseases are cardiovascular diseases (first cause of death in developed countries),
cancer (second cause of death in developed countries) and chronic respiratory diseases (third cause of death in
developed countries). They are so common that one out of three people in Spain (or any other developed
country) will die from cardiovascular disease and one out of three people in Spain (or any other developed
country) will die from cancer (one out of two people in Spain will suffer from cancer and one out of
three will die).
To prevent non-infectious diseases it is recommended not to smoke, do exercise and eat a
healthy diet.
HOW INFECTIOUS DISEASES ARE TRANSMITTED
In general, you can get infectious diseases in any of 5 different ways: through person to
person (directly by direct contact or indirectly by touching objets), air, food, water and animal bites.
1- By person-to-person:
A)- Indirectly: by touching objects such as a doorknob or telephone (when you touch
a doorknob handled by someone ill with the flu or a cold, for example, you can pick up the
germs he or she left behind. If you then touch your eyes, mouth or nose before washing your
hands, you may become infected).
B)- Directly: through direct contact. The microorganism passes directly from an ill
person to a healthy person by sexual contact (for example AIDS) or when the ill one touches,
coughs on or kisses someone (for example the flu or a cold).
2- By breathing contaminated air: you take pathogens into your body when you breathe,
becauses some microorganisms are suspended in the air (either freely or on dust particles). Tuberculosis
is transmitted this way.
3 y 4- By drinking water or eating food which are contaminated with pathogenic
microorganisms. Cholera is an example of a disease transmitted by drinking contaminated water and
salmonella is caused by eating foods which are in a bad state.
5- Through animals that transmit the diseases. For example malaria and sleeping sickness are
transmitted by insects: the protozoa that cause malaria is transmitted by the bite of a tropical
mosquito and the protozoa that cause sleeping sickness is transmitted by a bite from the tsetse fly.
¿Do you know another different way you can get an infectious disease?
SOME METHODS TO PREVENT INFECTIOUS DISEASES
Some infectious diseases can be prevented by vaccines. A good hygiene such as frequent
hand-washing also protects you from infectious diseases and healthy habits (eat a well-balanced diet,
exercise daily, getting sufficient sleep at night, avoid consuming tobacco...) can keep the body and
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immune system strong enough to fight against microorganisms. Only consume food and drink in
good condition.
IMMUNITY AND VACCINES
White blood cells fight against microorganisms that invade our tissues. The most important
ones are phagocytes and lymphocytes. Phagocytes are non-specific defenses because they ingest and
kill any pathogens they encounter. Lymphocytes are specific defenses that have specific antibodies
that only attack a specific pathogen´s antigen. Antigens are
specific molecules on a pathogen´s surface, different pathogens
have different antigens, so every specific lymphocyte only
attacks a specific pathogen that has the antigens that are
recognised by a lymphocyte´s antibodies. An antibody is a ”Y”shaped molecule that bind to an antigen that matches its
particular shape.
Images of phagocytes engulfing and destroying microorganisms:
Images of lymphocytes producing and releasing antibodies:
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When the antibodies bind to the antigens on the microorganism. This makes the
microorganism much less harmful and facilitates its destruction by other cells because antibodies
mark pathogens for destruction (when the phagocytes “see” the antibodies on a pathogen they ingest
and kill the pathogen more effectively).
Resistance to a particular disease is called immunity. Individuals who recover from an
infectious disease develop an immunity to that disease because the specific lymphocytes of that
specific disease become memory cells that provide lifelong protection (immunity) against that
specific disease (pathogen). If the pathogen ever appears again memory cells activate antibody
production against that pathogen much faster than the first time it happened without memory cells,
then antibodies destroy the pathogen before you become ill. It is so fast and effective that you are not
even aware of the battle going on in your body and you are said to be immune to that pathogen.
A vaccine is a preparation which contains pathogens that cause an infection, but they have
been deactivated, so that they do not cause any harm. They are injected into the body, lymphocytes
recognise the antigens and they produce the antibodies to fight them and the memory cells that give
us immunity.
TRANSPLANTS
Organ and tissue donations are medical processes that save and transform lives. Organs and
tissues are removed from a donor and transplanted into someone (recipient) who could be very ill or
dying from tissue or organ failure. One organ and tissue donor can save the lives of up to 10 people
and significantly improve the lives of many more. Blood transplant is called transfusion. The main
problem with transplants is the rejection of the organ or tissue (the recipient white blood cells attack
the new organ or tissue.
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