What is disease?
- A disease is defined as a physical or mental disorder or malfunction with a characteristic set of signs or symptoms.
- Diseases may be caused by a single factor such as a pathogenic microorganism or be multifactorial and have many causes some of which may depend on lifestyle.
- Pathogenic microorganisms include bacteria, viruses and fungi.
- Each pathogen has a specific method by which it causes disease. Some such as the influenza virus damage host cells whereas others, such as Vibrio cholera produce toxins which have a harmful effect on the body.
- The ability of the pathogen to cause disease depends on
- Location - what tissue is colonised
- Infectivity - how easily a bacterium can enter the host cell
- Invasiveness - how easily a bacterium or its toxin spreads within the body
- Pathogenicity - how a bacterium causes disease
- Common entry points for pathogens are the gas exchange and digestive system.
- A healthy lifestyle involves:
- Maintaining a healthy weight
- Taking regular exercise
- Eating a balanced diet
- Drinking a limited amount of alcohol
- Not smoking
- Lifestyle has an effect on human health:
- Exposure to carcinogenic chemicals (i.e. those found in tobacco smoke) or radiation (i.e. X-rays) may increase a person's chance of contracting cancer
- Coronary heart disease is associated with diets that are rich in fat and a sedentary lifestyle
- Alterations to a person’s lifestyle can have a dramatic effect on the likelihood of them contracting these conditions