Causes of disease

A disease is defined as a physical or mental disorder or malfunction with a certain set of signs or symptoms.

Diseases may be caused by a single factor such as a pathogenic microorganism or have many causes some of which may depend on lifestyle.

Pathogens have many qualities that assist with the causing of diseases: they can gain entry to the host, colonise tissues of the host, resist defences of the host and cause damage to the host’s tissues. Microorganisms gain entry to the host through the skin and through exchange sites. For example, if someone has physical contact with an infected individual. All these characteristics lead to a disease occurring in the host. Some examples of pathogens are bacteria, viruses and fungi. A healthy lifestyle involves, maintaining a healthy weight, taking regular exercise, eating a balanced diet, drinking a limited amount of alcohol and not smoking. If individuals lead a healthy lifestyle, the risk of contracting a disease will decrease. For example, the carcinogenic chemicals found in tobacco smoke may increase an individual’s risk of contracting cancer. However, people need to remember that it’s never too late to change your lifestyle. For example, there is clear evidence showing that the risk of lung cancer to a smoker is reduced if they stop smoking. Going into more detail about the pathogen, we can understand what consequences the production of toxins can cause. A toxin is a harmful chemical that damages the body. For example, the bacterium that causes tetanus produces a toxin that blocks the function of certain nerve cells, causing muscle spasms. Pathogenic microorganisms can also damage the host’s cells. They do this by rupturing them to release nutrients inside them (e.g. protein), breaking down nutrients inside the cell for their own use (this starves and eventually kills the cell) and replicating inside the cell causing them to burst when released - many viruses do this. Cholera bacteria produce a toxin that can cause havoc in the host’s body: it causes chloride ion protein channels in the plasma membranes of the small intestine epithelial cells to open. This causes the chloride ions to move into the small intestine lumen – this lowers the water potential of the lumen - (Lumen refers to the cavity or channel within a tube or tubular organ). To try and balance the water concentration, water will move out of the blood and into the small intestine lumen by osmosis. The massive increase in water secretion into the intestine lumen leads to horrifically bad diarrhea, causing the body to become extremely dehydrated. This is another example of how disease is caused and the causes of diseases. Oral rehydration solutions are used to treat diarrheal diseases like cholera because many underprivileged areas do not have access to a drip - when fluid is inserted into the body directly through a vein. This can cause many ethical issues. For example, most diarrheal diseases effect children, meaning the oral rehydration solutions are now tested on children. However, the parents decide whether the child will participate in the trial, the child does not get a say. Many people argue that this is unethical and it can cause conflicts.

One thing that helps our body cope with a disease is our white blood cells. We rely on our white blood cells to resist disease by destroying and ingesting the pathogens and to produce antibodies and antitoxins that destroy pathogens and counteract the toxins released by the pathogens. However, certain diseases affect and destroy our white blood cells, which causes our immune system to deteriorate. An example of this is AIDS, which is caused by the HIV Virus. This is an infections disease, which is transmitted through unprotected sex, through infected bodily fluids (e.g. sharing needles) and from mother to fetus through the placenta. The virus reproduces inside the cells the organism has infected. After the virus has reproduced, it kills the white blood cells as it leaves. The immune system deteriorates and eventually fails due to the loss of white blood cells. It causes the sufferer to be more vulnerable to other infections. Many diseases are also caused by parasites and are infectious between the infected. For example, malaria is caused by a parasite called Plasmodium. Because the disease is passed through the bloodstream, it can only be transmitted via organ transplant, blood transfusion and pregnancy. However, the carrier mostly transmits the disease, which in this case is the mosquito. These are insects that feed on the blood of animals, including humans. The mosquitos are vectors – they don’t cause the disease themselves, but they spread the disease by transferring the parasite from one host to another. The parasite Plasmodium infects the liver and red blood cells and disrupts the blood flow to major organs. This is another example of how disease is caused. The causing of many diseases, such as AIDS, malaria and tuberculosis, can have a global impact. They can have a destructive effect on developing countries because they lack health care. All these diseases are very common in these areas. This is because there is lack of family planning, sexual/health education and medical equipment. As well as this, there are overcrowded conditions, which increases the chance of infection from one host to another. These diseases can slow down social and economic development due to the increasing death rate – less workforce. This shows that disease acts as a gateway to devastating consequences. Diseases may also be caused by genetic defects, nutritional deficiencies and other environmental factors. For example, an extra chromosome causes Downs Syndrome. Iron Deficiency Anaemia occurs when your body lacks iron, an essential nutrient. It is a nutritional deficiency and leads to the decreased production of red blood cells in the body. Red blood cells carry oxygen around your body, meaning that if you deprive your body of this, the essential organs and tissues in your body will not get as much oxygen as they need, causing fatigue, breathing difficulties and heart palpitations. Many women contract anaemia during pregnancy, as the body needs extra iron to supply a sufficient blood stream to the baby, as well as the correct nutrients. Others contract the disease through lack of iron in the diet (though this is rare) and Gastrointestinal blood loss - Your gastrointestinal tract is the part of your body responsible for digesting food. It contains the stomach and intestines.
Bleeding in the gastrointestinal tract is the most common cause of iron deficiency anaemia in men, and in women who have been through the menopause. Bronchitis is a disease that effects the main airways of the lungs, causing them to become irritated and inflamed. Bronchitis can be caused by environmental factors such as breathing in irritant substances (smog or chemicals). The most common cause of this disease is smoking or passive smoking. All of these are environmental factors. As well as this, you may also contract this disease through your chosen occupation. For example, if you work in a clothes factory, inhaling fabric fibres could cause bronchitis. Inhaling substances such as grain dust, chlorine and strong acids could also cause this disease. This shows how environmental factors can cause disease.

To me, cancer is one of the most interesting diseases. This is because no one can fully understand the causes, meaning it becomes more difficult to cure. Cancer still manages to be one of the hardest diseases to battle. Although medical breakthroughs are continuous and frequent, there are more than 200 types of cancer; all with different levels of danger, meaning it is hard to tackle every single one. There is no cause to cancer, only factors that can increase your risk of contracting it. This means cancer is multifactorial – one single factor cannot cause cancer (e.g. a pathogen), but many factors can increase the risk. Anyone could get cancer. For example, tobacco smoke that you breathe in may help to cause lung cancer and overexposing your skin to the sun could cause a melanoma on your leg – the key words here being ‘may’ and ‘could’, showing that there is no definite cause.
Breast cancer is the most common cancer in the UK. About 48,000 women get breast cancer in Britain each year. Most are over 50, but younger women, and in rare cases, men, can also get breast cancer. The causes of breast cancer are not fully understood, which is why it is hard to understand why one woman contracts breast cancer and another does not. Breast cancer, just like other cancers, has many risk factors such as being obese, being exposed to oestrogen or being taller than average. Prostate cancer is the most common cancer in men in the UK, with over 40,000 new cases diagnosed every year. The causes of prostate cancer are largely unknown. However, a number of things can increase your risk of contracting the disease. Your chance of developing this type of cancer increases with age. Most cases occur in men over 50 years of age. Prostate cancer is more common in men of African-Caribbean or African descent, and less common in men of Asian descent. The reason for this is unknown, as is the cause of this disease.

HELPFUL SOURCES USED

http://www.slideshare.net/hannahtweddle/biology-unit-1-causes-of-diseases

http://www.biologyguide.net/biol1/1_disease.htm

Book: CGP AS-LEVEL BIOLOGY

http://www.nhs.uk/Conditions/Anaemia-iron-deficiency-/Pages/Causes.aspx

http://www.cancerresearchuk.org/cancer-help/about-cancer/causes-symptoms/causes/what-causes-cancer