THE CAUSES OF DISEASE IN HUMANS – 25 MARKS
Disease is a malfunction of the body which has a harmful effect on good health. Malfunction in the body can be caused by or affected by pathogens, lifestyle and genetics and can affect the mental, physical and social aspects of an individual.
Microorganisms such as pathogens, bacteria and viruses can cause disease in a number of ways. Pathogens can cause damage to a host’s tissues by preventing the tissues from functioning properly or by breaking down the membranes of the host cells. Once a pathogen colonises a host cell, it releases toxins or damages the host cell membrane. Viruses inhibit the synthesis of DNA, RNA and proteins by the host cells. Some pathogens divide within the body in a few hours and some can take days.
A disease such as cholera is caused by Vibrio Cholerae bacterium which is transmitted to the body by the ingestion of contaminated water or food. The bacteria reach the small intestine and use their flagella to penetrate through the lining of the intestine wall. They produce a toxin which binds and opens chloride ion channels in the epithelial cells. This causes an influx of chloride ions into the lumen of the intestine. This lowers the water potential inside the lumen causing water to flow from the cells into the lumen. A water potential gradient is then established which causes water to flow from body tissues and the blood into the intestine by osmosis. This causes dehydration and severe diarrhoea.
Tuberculosis is also another infected disease that is caused by the bacteria Mycobacterium tuberculosis or Mycobacterium bovis. Pulmonary tuberculosis is spread by air droplets spread in the air by cough, sneeze, laugh or talk. It can be easily spread in a family, workplace or crowded areas. M.Bovis can infect cattle, which then produce infected milk, which humans ingest. Once the bacteria are in the body, they grow and divide within the upper regions of the lungs where oxygen supply is high. The immune system and white blood cells attack these bacteria, which causes an inflammatory response. The infection can be controlled but sometimes some bacteria remain in the lungs for many years until they attack again. They destroy the tissues in the upper region of the lungs. This causes scar tissue, which the body then tries to remove the damaged tissue by coughing with some blood.
Antibiotics are used to treat bacterial diseases. If an antibiotic dose is not completed over a given time period or even if is over-used, the bacteria strains can become antibiotic resistant. They become like this when mutations occur and this causes the bacteria to change shape or structure, therefore making it resistant to the antibiotic. The survivor bacteria now have the gene which is resistant to antibiotics. The resistance can then be transmitted to other cells by horizontal gene transmission, where plasmids containing the resistant gene are transferred from cell to cell by conjugation. This leads to antibiotics having no effect on the human body, and the bacteria can now colonise host cells and cause disease/infection.
Lifestyle and diet can also play a major role in developing a disease. A disease such as coronary heart disease (CHD) is caused by unhealthy diets which are high in saturated fat and cholesterol. The fat builds up in the lining of the artery wall (atheroma) and causes less blood/oxygen to flow to the heart, leading to tissues in the heart to stop working, which could cause a myocardial infarction. A diet with high levels of salts can cause high blood pressure in the body, which can lead to a blood clot forming in veins/arteries. The blood clot restricts blood flow and can also burst the artery/vein causing internal bleeding.
Emphysema is a lung disease caused by smoking. Individuals with emphysema have permanently stretched elastin protein which allows our lungs to stretch and spring back when we breathe in and out. A permanently…