Causes of disease in humans
A disease is usually a medical condition that affects the body of an organism. In humans, disease is often broadly used to refer to any condition that causes pain, dysfunction, distress or death to the person affected. In this sense, it sometimes includes injuries, disabilities, disorders, syndromes, infections, etc.
The most common cause of disease in humans is via pathogens; microorganisms such as viruses, bacteria, protozoa, and fungi that cause disease in humans and other species that enter the body in a number of ways. This includes the digestive system and the gas exchange system. Once inside the body, pathogens may cause disease by damaging cells or producing toxins that affect the cells in the body. One example of a pathogen is the cholera bacterium. This enters the small intestine through the digestive system and releases toxins that bind to the receptors on the epithelial cells. This causes the protein channels for chloride ions to open, resulting in an influx of chloride ions into the lumen. The movement of ions raises the water potential and lowers the water potential in the lumen. Water is then drawn out of the cells via osmosis. Therefore creating a concentration gradient due the loss of ions from the intestinal epithelium, thus ions from the surrounding tissues and blood diffuse into the cells. Water then flows out of these tissues and into the lumen, resulting in severe dehydration and diarrhoea which form the symptoms of cholera. Viruses affect organisms in a different way. They cause disease invading a cell which is called a host and damage the cell from the inside. After the host is infected, the virus enters the cell and implants its genetic information, forcing it to create multiple viruses by replicating the viruses’ genetic information. Once hundreds of viruses have been made, the cell is destroyed and the viruses go on to infect other cells and continue reproducing. Fungal...
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