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 diseases mainly affect organisms externally, targeting interfaces such as skin with infections such as Thrush. Thrush is a yeast infection and its main symptom is causing inflammation of the general area resulting in discomfort to the host. Another pathogen that causes disease is Pulmonary Tuberculosis.
Caused by bacterial infection, it’s transmitted via droplet infection in which it’s spread through sneezing or coughing and an uninfected person takes in the droplets by inhaling them into the lungs. The bacteria reproduce and destroy the lung tissue, prompting an immune response that brings the infection under control and repairs the lung damage is. However, the infection may re emerge years later as secondary TB. This occurs as in some cases as the phagocytes surround and ingest the bacteria but the bacteria have a thick waxy coat and are not killed by the white blood cells.
The TB bacteria start to destroy the lung tissue, causing multiple lesions appear on the lungs called tubercles and the bacteria may spread to both lungs and to other organs such brain. The patient coughing up damaged lung tissue and blood and becoming very short of breath are just a few of the symptoms. Disease in humans can also be caused by defects in the genetic code. This results when mutations occur, which is a change in the sequence of nucleotide bases in the genetic code.
The mutation, a change in the base sequence of the DNA, will mean that the mutated amino acids with code for a different polypeptide. As a result, the protein will have a different tertiary structure and may not be able to carry out its function because the active site of the enzyme has changed shape, thus it is no longer complementary to the substrate. Therefore, a non-functioning protein to be synthesized and it results in the enzyme not being able to perform certain functions such as forming enzyme-substrate complexes.
Another disease with genetic causes, specifically a mutation, which occurs in humans, is cancer. Cancer is a disorder of cell growth that is caused by rapid cell division that is uncontrollable, resulting in invasion and the destruction of the surrounding healthy tissue. Proto-oncogenes are the genes responsible for increasing the rate of cell division in humans. They code for growth factors that attach to receptor proteins on cell surface membranes in order to stimulate the genes necessary for DNA replication.
Proto-oncogenes mutate and instead form oncogenes which cause cells to divide too rapidly. Tumour suppressor genes, which slow down the rate of cell division, mutate and are instead inactive. An inactive, mutated tumour suppressor gene is not able to slow down cells division. Cancer arises when a person develops both a oncogene and mutated tumour suppressor genes, thus the rate of cell division is unable to be controlled. This results in uncontrolled rapid cell division and therefore the development of a cancerous tumour.
Cite this Causes of Disease in Humans
Causes of Disease in Humans. (2016, Sep 29). Retrieved from https://graduateway.com/causes-of-disease-in-humans/