691
CHAPTER SEVENTEEN
Digestive System
intestinal tract. The diarrhea is often not bloody,
and complications such as cancer are rare.
Overall, about 20% of people with symp-
toms of irritable bowel disease seem to fall
between the descriptions of ulcerative colitis and
Crohn disease and are classiF
ed as having “inde-
terminate colitis.” Surgery is sometimes used to
treat in±
ammatory bowel disease. Autoimmunity,
infection, or a genetic predisposition may con-
tribute to causing in±
ammatory bowel disease.
Colorectal Cancer
Cancer of the large intestine or rectum, known
as
colorectal cancer,
is the fourth most preva-
lent cancer in the United States and the second
most common cause of cancer death. More than
30,000 new cases are diagnosed each year, and
more than 56,000 people die of the condition. It
tends to run in families.
Symptoms of colorectal cancer include
a change in frequency or consistency of
bowel movements
blood in the feces
a narrowing of feces
abdominal discomfort or pain
weight loss
fatigue
unexplained vomiting
Diagnostic tests can detect colorectal can-
cer, described in table 17A. These tests are of
two general types—the fecal occult blood test
T
he large intestine (colon) is the source of
familiar digestive discomforts as well as
more serious disorders.
Diverticulosis and Inf
ammatory
Bowel Disease
In diverticulosis, parts of the intestinal wall
weaken, and the inner mucous membrane pro-
trudes through. If chyme accumulates in the out-
pouching and becomes infected (diverticulitis),
antibiotics or surgical removal of the area may
become necessary. Lack of dietary F
ber may set
the stage for diverticulosis. The condition does
not occur in populations that eat high F
ber diets,
and began to appear in the United States only
after reF
ned foods were introduced in the middle
of the twentieth century.
Inflammatory bowel disease is a group of
disorders that includes ulcerative colitis and
Crohn disease. They di²
er by the site and extent
of in±
ammation and ulceration of the intestines.
In the United States, about 100,000 people su²
er
the abdominal cramps and diarrhea of ulcerative
colitis, and 500,000 individuals have similar symp-
toms of Crohn disease.
Ulcerative colitis a²
ects the mucosa and sub-
mucosa of the distal large intestine and the rectum.
In about 25% of cases, the disease extends no far-
ther than the rectum. Bouts of bloody diarrhea and
cramps may last for days or weeks and may recur
frequently or only rarely. The severe diarrhea leads
to weight loss and electrolyte imbalances and may
develop into colon cancer or a²
ect other organs,
including the skin, eyes, or liver. The in±
amed and
ulcerous tissue is continuous.
Crohn disease is more extensive than ulcer-
ative colitis, extending into the small and large
intestines and penetrating all tissue layers. In
contrast to the uniformity of ulcerative colitis,
ected portions of intestine in Crohn disease are
interspersed with una²
ected areas, producing a
“cobblestone” e²
ect after many years. The ileum
and cecum are a²
ected in about 40% of a²
ected
individuals, only the small intestine is involved
in 30% of cases, and only the large intestine is
involved in 25% of cases. Rarely, the disease
affects more proximal structures of the gastro-
performed on a stool sample and imaging the
large intestine wall. In development is a test that
screens the DNA from cells in feces for mutations
associated with colorectal cancer.
A rite of passage for those over fifty is
F
beroptic colonoscopy. Under sedation, a ±
exible
lit tube is inserted into the rectum, and polyps
and tumors are identified and removed. Those
with a family history of colon cancer should be
screened at an earlier age. ³iberoptic colonos-
copy takes less than an hour. A newer procedure,
computed tomographic colonography (popu-
larly called a virtual colonoscopy), requires the
same preparatory bowel cleansing, but does not
require sedation and is faster. However, if a lesion
is detected, the more invasive approach must be
used to remove the suspicious tissue.
Treatment for colorectal cancer is to remove
the a²
ected tissue. If a large portion of the intes-
tine is removed, surgery is used to construct a
new opening to release feces. The free end of
the intestine is attached to an opening created
through the skin of the abdomen, and a bag is
attached to the opening to collect the fecal mat-
ter. This procedure is called a colostomy.
³or people who have a certain inherited
form of colon cancer (familial adenomatous poly-
posis), nonsteroidal anti-inflammatory drugs
(NSAIDs) called
Cox-2 inhibitors
are used to treat
the disease and may even help to prevent it in
those identified by a genetic test to be at high
risk. However, these drugs increase the risk of
heart disease in certain individuals.
17.5
CLINICAL APPLICATION
Disorders of the Large Intestine
TABLE
17A
|
Diagnostic Tests for Colorectal Cancer
Diagnostic Test
Description
Digital rectal exam
Physician palpates large intestine and rectum
Double-contrast barium enema
X-ray exam following ingestion of contrast agent highlights
blockages in large intestine
³ecal occult blood test
Blood detected in feces sample
Colorectal cancer gene test
(experimental)
Mutations associated with colorectal cancer detected in DNA of
cells shed with feces
Sigmoidoscopy
Endoscope views rectum and lower colon
Colonoscopy
Endoscope views rectum and entire colon
previous page 721 David Shier Hole's Human Anatomy and Physiology 2010 read online next page 723 David Shier Hole's Human Anatomy and Physiology 2010 read online Home Toggle text on/off