the outer lining (membrane) that covers the intestine.
Stricture: a narrowing of the central channel in a segment of the intestine, which can lead to obstruction or blockage.
Ulcer: an area in the gastrointestinal tract where there is a loss of the normal internal lining (mucosa). Ulcers can result in complications, such as bleeding or abscesses.
Villi: fingerlike projections of the inner lining of the small intestine (mucosa), which have the effect of increasing the amount of mucosal surface available for absorption of nutrients.
Smoking Paradox
Smoking increases the risk of developing Crohn’s disease, and in those already affected, smoking may make the disease more aggressive or severe. In contrast, smoking seems to protect against ulcerative colitis. Patients with ulcerative colitis are more likely to be nonsmokers or former smokers than a similar group of people selected from the general population. In former smokers, the period soon after smoking cessation seems to be a time of particularly increased risk of developing ulcerative colitis. This observation has led some researchers to use nicotine, in the form of skin patches, as a treatment for ulcerative colitis. Despite the strong association between cigarette smoking and protection against ulcerative colitis, this approach to treatment has not been consistently effective.
Who Gets Inflammatory Bowel Disease?
The onset of inflammatory bowel disease may be influenced by age, gender, and geography.
Age Factors
Crohn’s disease and ulcerative colitis most commonly begin in young people. Although it is unusual to see this disorder in children below the age of 5, there is an increase in the occurrence of IBD up until the age of 20, with maximum incidence in the age group between 20 and 40. It is less common, but certainly not unheard of, for older individuals in their 50s and 60s to first experience IBD. The first onset of disease is quite rare in the elderly. When symptoms first occur in someone from that age group, the attending doctor will usually consider other conditions or illnesses as more likely than IBD.
Gender
Inflammatory bowel disease appears to occur in males and females at roughly the same rate, although some studies have suggested that there may be slightly higher incidence in females. These differences may vary depending on the age of the first onset of IBD, but even if such differences exist, they are likely to be minor and of no major significance.
Population Studies
Although they are generally thought to be diseases that are found more frequently in developed countries, Crohn’s disease and ulcerative colitis have been observed in every race and in every country that has been specifically studied. There do appear to be some interesting differences between countries, as well as between ethnic groups within a given country.
These diseases are much less common in Asia, but this may be changing. In Japan, for example, Crohn’s disease was almost unheard of over half a century ago, but there appears to have been a steady increase in the incidence since then. The incidence in the Jewish population is among the highest of any ethnic or racial group. However, within the Jewish population, there appears to be a difference in incidence depending upon the country of origin. In one study, the incidence of IBD was higher in Jews of Ashkenazi (European) descent than in Jewish populations of Sephardic (Northern African and Middle Eastern) descent.
The varying risks of IBD in different countries are not entirely due to purely inherited or genetic reasons. The increasing incidence of Crohn’s disease observed in Japan suggests that environmental factors have an important effect on the risk of developing IBD. In addition, studies of South Asian immigrants to North America have shown that the individuals who immigrate keep the lower risk of IBD that is seen in their country of origin, whereas their children, who are generally born and raised in North America, have a higher risk of developing IBD in their lifetime. These variations in the incidence of IBD provide clues as to the possible contributing factors or causes and have led to a number of interesting theories and questions that are undergoing further testing.
North-South Gradient
The incidence of IBD has generally been highest in North America and Northern European countries and lower in the countries at more southerly latitudes. This has been described as a “north-south gradient.” However, this gradient is not unique to the north-south comparison but probably reflects an underlying gradient between developed and developing countries.
Where in the Body Does IBD Occur?
Inflammatory bowel disease occurs in specific sections of the gastrointestinal tract, or gut. Before considering what has gone wrong in Crohn’s disease and ulcerative colitis, we need to understand how a healthy gut works. The normal functioning of the intestinal immune system may go awry in inflammatory bowel disease.
Critical for Life
The gastrointestinal tract serves several critical functions that help to keep us alive. It allows nutrients, water, minerals, and vitamins to enter our body while keeping out harmful substances.
Functions of the Gastrointestinal Tract
The gastrointestinal tract is a tubular structure that extends from the mouth all the way down to the anus. The gut has two vital functions — nutrient absorption and immune protection.
Principal Parts of the Gastrointestinal Tract
Nutrient Absorption
The primary job of the gut is to take in and absorb nutrients. These nutrients provide the building blocks and fuel needed to maintain all other bodily functions. The gut absorbs water, minerals, and vitamins from the food and drinks that are ingested.
Immune Protection
At the same time that it allows or promotes absorption of nutrients, the gastrointestinal tract must keep numerous potentially harmful items out of the body. These include microscopic organisms, such as bacteria, viruses, and parasites, as well as certain dangerous proteins that may cause disease if absorbed into the body from the gut. The gastrointestinal tract is, therefore, an important part of the body’s immune system.
Principal Parts of the Gastrointestinal Tract
The gastrointestinal tract has six major components: mouth, esophagus, stomach, small intestine, large intestine, and anus. These may all be affected by inflammatory bowel disease.
Mouth
The mouth and the structures within it (lips, teeth, tongue, and palate) are involved in the ingestion of food. The teeth allow the grinding of food into small particles that are more easily broken down and digested by the enzymes present farther down in the intestine. The lips, tongue, and palate assist with the chewing and swallowing of food.
Esophagus
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