A-level Biology/Human Health and Disease/introduction
Health is more than just being free from disease - it is a good physical feeling, a well-adjusted, positive individual who is able to undertake the tasks of their day without much difficulty.We also say "HEALTH IS WEALTH".
Disease is as broad a term as health is - but simply it is a disorder or malfunction of the mind or body which stops good health. Diseases usually have more than one factor - i.e. an attempted suicide might be a self-inflicted physical disease. Acute diseases are sudden onset, rapidly changing disease with a short life-span, whereas chronic are diseases that continue for a long time (months or years).
|Deficiency||Unbalanced or inadequate diet.||Nutritional disease cause by an unbalanced or inadequate diet. Can lead to starvation.||Scurvy|
|Degenerative||Gradual decline in function||Repair mechanisms failing, immune system begins to attack itself.||Alzheimers, strokes, cancers.|
|Infectious||Organisms invading the body||Pathogens causing disease within the body, can be transmitted from person to person||Malaria|
|Non-Infectious||Not pathogens||Any disease that is not caused by a pathogen.||Stroke|
|Inherited||Faulty genes||A disease that is passed from parents to their children by a faulty allele.||Cystic fibrosis (see further description below)|
|Mental||Changes to the mind, possibly with a physical cause.||Any disease that affects a person's mind. Sometimes a visible degeneration of brain tissue is present, as in CJD.||CJD, Alzheimer's, dementia, schizophrenia.|
|Physical||Damage to the body||Permanent or temporary damage to any part of the body||Leprosy, broken leg.|
|Self-Inflicted||Self||Willful damage to own persons body by themselves.||Attempted suicide|
|Social||Social environment or behaviour||How a persons life affects their health, exposing or protecting them from certain diseases.||Hypothermia, CHD|
Cystic Fibrosis 
Cystic fibrosis is an inherited disease, and is the most common in Britain. The disease is because of fault in a gene coding for a channel protein that is meant to allow chloride ions to flow out of cells, and since chloride ions take water with them this presents a problem. If neither move out, the alveoli is hindered by a thick sticky mucus, making breathing difficult and forming a breeding ground for bacteria, resulting in infections. Regular physiotherapy can help to loosen and remove the mucus.
There are two versions of every gene in each of the bodies cells, called alleles. There are two types of alleles - dominant and recessive, and cystic fibrosis is caused by a recessive allele. Let's say that A is the healthy allele, and a is the cystic fibrosis allele, and is recessive. Someone with AA is healthy, someone with Aa is a carrier but is healthy (because the healthy A is dominant over the unhealthy a). Two people with Aa and Aa are both healthy, but if they produce a child there is a 1/4 chance that this child will have the genotype aa, which means they will suffer from cystic fibrosis.
Degenerative Diseases 
There are three major types of degenerative disease;
- Diseases of the skeletal, muscular and nervous systems. Alzheimer's, motor neurone disease.
- Cardiovascular diseases. Coronary Heart Disease and strokes
Epidemiology is the study of the occurrence, distribution, and control of diseases in populations. The statistics reflect the amount of people who are ill and the amount that have died and are particular to a population under the study. Three types of data provide information on the spread of disease - incidence, prevalence and mortality. This refers to the number of new cases per time period, the number of people in a population with the disease and the amount of people who have died from the disease, respectively.
Epidemiology can be used by a variety of people for many things. One of its most important uses is by governments to increase funding for research into rising causes of death, such as AIDS was in the 1980s. They can also show differences between economic levels and separate countries, or promote mass screening to prevent disease before they start, such as cervical cancer.
Disease Descriptions 
- Endemic - Disease is always present in the population. TB is an example.
- Epidemic - Disease spreads rapidly to affect many people. Influenza is an example.
- Pandemic - Disease spreads over a very large area. AIDS is an example.
Disease patterns 
In developed countries, disease such as CHD and cancer are much more common than in third world countries. This is as a result of developed countries having better health care, including vaccination and treatment against serious infectious diseases such as measles, polio, TB and malaria. Also, smoking and foods high in fat are more prevalent in developed countries. Attitudes towards drinking, smoking or obesity may affect a countries overall incidences of disease - for example, incidences of lung cancer are expected to fall following the United Kingdom's smoking ban as it forces people to quit and reduces the effects of secondary smoke.