No.15
The causes of disease in humans
A disease is a medical issue within the body, defined as a physical or mental disorder. It come with a characteristic set of signs or symptomswhich has negative effects on the sufferer. The symptoms develop as the infection attacks the body. There aremanydifferent causes of disease in humans.Diseases may be pathogenic,geneticormay be caused by lifestyle choices of anindividual or people surrounding them.
Pathogens which are microorganisms such as bacteria, virus and fungi are the most common cause of disease. There are four types of pathogen: bacterium, virus, fungi and protozoa. Pathogens can be airborne e.g. cold virus or waterborne e.g. cholera and can be passed on this way. Pathogens enter our body via various means.They can eitherenter through breakages in the skinorenter through our respiratory and digestive systems.However, eachtype ofpathogen hasaspecific methodof howit causes disease. When a pathogen enters our body, it may secrete a harmful molecule called a toxin which can damage cells or interfere with the bodily functions (metabolism). For example, tetanus toxins block the functioning of certain nerve cells causing muscle spasms.There are other pathogenswhichmay damage cells physically by entering the host cell and using up its nutrients to reproduce inside and burst the cell or rupturing the cell membrane.
A common disease example of a toxin producing bacterium, would be Cholera. Cholera is transmitted byconsumingwater or foodsthat contain the bacteria; once a bacterium gets to the small intestine, it buries itself within the mucus lining of the intestine wall, and beings releasing toxic proteins. The toxin attaches toeitherthe carbohydrate receptors on the cell surface membrane of the epithelial cells,orthe other part actually enters the epithelial cells. The toxincausesthe ion channels of the epithelial cell open, causing ions to enter the intestine. Therefore, there isa loss of chloride ions in the cells, increasing their water potential, and an increase in chloride ions in the intestine, lowering its water potential; water then moves from the cells to the intestine, causing dehydration anddiarrhoea, the two common symptoms of Cholera.
There are many other diseases that are caused by pathogens. Another example would be Tuberculosis. The Mycobacterium Tuberculosis pathogen causes the disease in humans. It is airborne, so enters the body through the gas exchange system. The bacteria begin infecting the top of the lungs; during primary infection this simply involves the lymph nodes becoming inflamed as the immune system floods the area with white blood cells. However, the secondary infection is much more violent and less easily controlled; the bacterium has remained dormant for a period of time, but re-emerges and again, attacks the upper area of the lungs, this time around though they cause more damage, over-whelming and destroying tissue, causing a build-up of scar tissue that leads t...
