2.1 - Health & Disease

Health and the factors that affect it

• Health is the state of physical and mental wellbeing - and, as the World Health Organisation puts it, of social wellbeing too, and not merely the absence of disease or infirmity.
• Being healthy is about more than just not being ill: someone who is physically fit can still be unhealthy if they have mental health problems or are socially isolated.
• A disease is a condition that impairs the normal functioning of an organism, and is one of the major causes of ill health.
• Both animals and plants can get diseases.

Causes of disease and ill health

• Infection by a pathogen - A pathogen invades the organism
• A mutation in an organism's genes
• Environmental conditions - E.g. a plant that doesn't get enough light won't grow properly
• Diet, lifestyle or life situation - A person's day-to-day circumstances

A disease shows itself through symptoms - changes in the organism that indicate disease is present - although these aren't always obvious, especially in the early stages.

Other factors that affect health

• Diet - A good, balanced diet gives the body what it needs, whereas a poor diet harms both physical and mental health
• Stress - Being under constant stress can cause health problems
• Life situation - This includes whether a person can get hold of medicines to treat illness and the things that help prevent it

Communicable and non-communicable disease

Diseases fall into two groups, depending on whether they can spread between organisms.

Communicable (infectious) diseases

• Can spread from one organism to another - between people, or between animals and people.
• Are caused by pathogens.
• Examples: measles and malaria.

Non-communicable diseases

• Cannot be passed between organisms.
• Tend to last a long time and get worse slowly.
• Examples: asthma, cancer, and coronary heart disease.

How diseases interact

• Different types of disease can interact, so that having one disease makes another more likely.
• A disease can also leave the body weakened, making it more susceptible to others.

Four main ways diseases interact

1. Immune system problem - Reduces the body's ability to defend itself against pathogens, raising the risk of communicable diseases such as influenza. For example, HIV damages the immune system, so a person with HIV who is then infected with the tuberculosis bacterium cannot fight it off and the disease progresses rapidly.
2. Viruses triggering cancers - Some viruses living in cells can trigger cancers. Infection with HPV (human papillomavirus) causes most cases of cervical cancer.
3. Immune reactions triggering allergies - An immune reaction set off by infection with a pathogen can trigger allergies, such as skin rashes or worsened asthma.
4. Physical ill health leading to mental illness - Severe physical ill health can lead to mental illness, such as depression, particularly when it affects a person's ability to carry out everyday activities.