Cystic Fibrosis Term Paper

Cystic Fibrosis Term Paper
By: Katherine Heuser
Written: May 11, 2002
Revised: August 14, 2002

Cystic Fibrosis (CF)is an inherited, genetic disease that affects the lungs, the digestive and reproductive tracts, the pancreas, the heart and the liver. It is caused by a mutation, or change, in a pair of genes called CFTR (cystic fibrosis transmembrane conductance regulator). CFTR helps to produce mucus, a mixture of salt, water and sugar. This mucus is waht helps to clean, lubricate and protect entry and exit passageways of the body cells, especially the cells of the lungs and pancreas.

Suprisingly enough, CF has been around for more than 52,000 years (Clausinusz 1995). Even though CF has many negative aspects, their is one benefit from being a carrier of the gene. Because of the mutation in CFTR, people who are carriers of the CFTR gene have only half as many of the choloride or salt channels in the cells that line their intestines. Because of this, carriers are protected against diarrhea-inducing bacteria like E. coli, Salmonella, Typhoid, and Cholera.

When a toxin like Cholera is introduced into the intestines, the body's reaction is to permanently open the chloride channels, causing the intestines to produce three to four gallons of fluid per day. This mass release of fluid is supposed to flush the toxin out of the body. However, it often backfires. Unless the water and salt that is released is quickly replaced the person can die of dehydration. In carriers of CF, only half of the channels open, so only half the anount of fluid is released. "Half as much fluid might be just the right amount to get rid of the toxin without the body succumbing to diarrhea,"(Gabriel 1995).

In the past when epidemics of Cholera were common, this gave carriers of CF an advantage, and the defective gene spread. Since the majority of non-CF carriers died, when two people got married, the chances that two carriers were marrying each other was increased. Cystic Fibrosis is therefore found mainly among people of northern European descent.

WHAT IS A GENE?

A gene is best thought of as a sentence made up of a string of letters. In a gene the letters represent chemicals. If one of those letters is removed or changed what the gene is supposed to do is altered, just lie if you were to take a letter out of a sentence the meaning would change.

The gene CFTR is supposed to allow chloride, or salt, ions to leave the cells that make mucus. When the salt leaves, so does water, thinning out the mucus. The mutation in the CFTR gene affects the people with the disease so adversely becauxe the mucus isn't able to be thinned. It becomes a thick, sticky slime that coats the surface of the lungs, pancreas and reproductive tract.

This slimy coating is especially damaging in the pancreas. The thick mucus prevents enzymes (proteins that digest food and provide the body with vitamins and nutrients) from traveling to the intestines. This prevents food from being digested well, especially fats, and usually results in malnutrition.

In the lungs this slime covers the airways and makes it hard to breathe. It also can cause multiple lung infections because the mucus is an excellent source of food for bacteria.

The effect that CF has on the heart is a delayed one. The heart is often put under undue amounts of stress because of the constant sicknesses that is associated with CF. As a person with CF becomes older the heart becomes inflamed from over-exertion and can fail. This condition combined with a severe lung infection like pneumonia, is a common cause of death in people with Cystid Fibrosis.

Cystic Fibrosis also causes it's sufferers to develop liver disease, or multilobular cirrhosis. Abnormal transportation of bile, which plays an important role in the absorption of fats in the intestines causes the liver to become diseased (Am. J Pathol 2002 May). Liver disease in people with CF is a result of irregular bile transportation and is callec Cystic Fibrosis-associated Liver Disease or CFLD)

Cystic Fibrosis is the most common genetic disorder in the United States, affecting 1 in every 2500 Americans. There are over 1300 mutations of CFTR that can cause Cystic Fibrosis, the most common being delta-F508 (News Physiol Sci 2001 Aug.). Because most cases of CF are caused by the delta-F508 mutation, it is possible to easily screen for carriers of Cystic Fibrosis or people who are carriers of the disease, meaning that they only have one half of the mutated pair of CFTR genes.

This disease produces a wide variety of symptoms, some more severe than others. The most severe symptoms of CF occur in the lungs and digestive tract. If left untreated, the thick mucus in the lungs will slowly build up on the cell surfaces and decrease the flow of oxygen to the body, resulting in clubbed or enlarged fingertips (Pediatr Pulmonol 2002 May). Accompanied by the mucus are thousands of bacteria, including the bacteria that cause pneumonia, bronchitis, and bronchiolitis. Bronchitis is an inflammation of the main airways of the lungs while bronchiolitis is the swelling and inflammation of the smaller tubes that branch off the bronchi and lead to the alveoli ( a small cell that holds air in the lungs). Normally snall hair-like projections called cilia on the surface of the bronchioles would move the bacteria ridden mucus up the throat to be coughed up. However, in people with CF, the thicker mucus prevents this natural removal and increases swelling in the lung's tissues. A person with CF must cough harder and longer to clear the mucus riddent bacteria out of the lungs. This, in turn, makes the airways swell and become smaller, inhibiting comfortable breathing.

In the lungs Cystic Fibrosis creates an unbeatable situation. The thick mucus causes infection, which releases white blood cells to fight the infection. However, the white blood cells do more harm than good because they cause the mucus to become thicker. To fight infection white blood cells break themselves down and empty into the mucus. The thicker mucus, in turn causes more coughing which causes even more inflammation. As the mucus builds up it can close of the smaller airways in the lungs, many of which are still filled with air. This causes a decrease in the amount of oxygen the lungs are receiving. The lack of oxygen produces a fatigued feeling accompanied by shortness of breath. As time passes, and more air-filled alveoli are closed off, the chest will take on a barrel-like appearance that is common in emphysema.

The symptoms in the digestive tract can be equally severe, and are usually the first sypmtoms to present themselves, these include bulky, oily, foul-smelling feces, and rectal bleeding called rectal prolapse. The most noted damage is done to the pancreas. The pancreas is the organ in the body that produces enzymes. The enzymes are released into the intestines where it breaks down the food that has been eaten and supplies the body with nutrients.