and the reason for this is unknown. IBS is also called
spastic colon.
DescriptionIrritable bowel syndrome is not a life-threatening
disorder and does not progress to any more serious
conditions, but it is the cause of about one of every 10
doctor visits in the United States. Its symptoms,
although not medically serious, are varied, change-
able, and intrusive enough to impact an individual’s
quality of life. IBS causes people to miss school or
work, avoid certain activities, and it interferes with
personal relationships.
IBS involves both the large intestine (colon) and
the small intestine. It is best described as a disorder in
which the all tests show that the bowel is structurally
normal—no infection, no tumors or polyps, no abnor-
malities in the cells lining of the intestinal wall. It is not
contagious, and it is not strictly inherited, yet the
individual with IBD has pain, cramping, and either
constipation, diarrhea, or alternating periods of both,
so something is clearly wrong.
IBS should not to be confused withinflammatory
bowel disease(IBD). Inflammatory bowel diseases
such asCrohn’s disease, ulcerative colitis, andceliac
diseasecause changes in the cells lining the wall of the
intestine. These cell abnormalities can be seen in sam-
ples (biopsies) taken from the wall of the intestine. In a
person who has IBD, the cells in samples taken from
the lining of the intestine look normal. Inflammatory
bowel diseases increase the risk of developing intesti-
nal cancers; IBS does not.Demographics
As many as one out of every five Americans has
symptoms of irritable bowel syndrome. The disorder
appearstobemostcommoninWesterncountries.How-
ever poor access to medical care, different cultural atti-
tudes toward illness, and the fact that the disorder is
neither life threatening nor contagious and does not
have to be reported to any central authority makes it
difficult to tell what the actual rates are in developing
countries. In Western countries estimates of the number
of people with IBD range from 9–23% of the population.
IBS occurs in both children and adults. About 14%
of high school students and 6% of middle school stu-
dents report IBD symptoms. In these groups, IBS
accounts for 4–5% of all absences from school. In
about half of all people who have the disorder, symp-
toms begin before age 35; 30% say that their symptoms
began in childhood. Most other people with IBS
develop symptoms between ages 35 and 50. Women
are two to three times more likely to have IBS than men.Causes and symptoms
The cause of IBS is unknown. Some researchers
believe that the bowel of people with IBS is inap-
propriately sensitive and overreacts to normal thingsNormal and diseased (center) colons. Areas of constriction in
the colon cause constipation, while areas of distention cause
diarrhea.(John Bavosi/Science Photo Library. Custom Medical
Stock Photo, Inc. Reproduced by permission.)
KEY TERMS
Idiopathic—Occurring from unknown causes.
Neurotransmitter—One of a group of chemicals
secreted by a nerve cell (neuron) to carry a chem-
ical message to another nerve cell, often as a way of
transmitting a nerve impulse. Examples of neuro-
transmitters include acetylcholine, dopamine,
serotonin, and norepinephrine.
Rectum—The last few inches of the large intestine.Irritable bowel syndrome