HUMAN BIOLOGY

DiGestioN aND NUtritioN 209

Cancer of the colon or rectum—or colorectal cancer—
is one of the most frequently diagnosed cancers in the
United States. It accounts for about 20 percent of all cancer
deaths. The first internal sign of colorectal cancer may be
a round, depressed area of abnormal cells. Another com-
mon early warning sign is a growth called a polyp that
develops on the colon wall and becomes malignant (Figure
11.17). Fortunately, many precancerous growths and early
cases of colon cancer can be detected by colonoscopy. After
the patient is mildly sedated, a physician inserts a viewing
tube into the colon and can examine it for polyps and other
signs of disease.
Outward signs of colorectal cancer include a change in
bowel habits, blood in feces, or rectal bleeding. People over
age 50 have the highest risk. The tendency to develop pol-
yps, and colorectal cancer, can run in families, but usually
there is no obvious genetic link. Because colorectal cancer is
much more common in Western societies, some experts have
proposed that the typical high-fat, low-fiber Western diet
may be a factor, and there is a lot of active research on the
issue. Studies suggest that low doses of aspirin or NSAIDs
(non-steroidal anti-inflammatory drugs such as ibuprofen)
may reduce the risk of developing precancerous polyps.
Chapter 22 looks in more detail at the causes of cancer.

malabsorption disorders prevent nutrients

from being properly absorbed

Anything that interferes with the small intestine’s ability to

take up nutrients can lead to a malabsorption disorder.

As many as 50 million adults in the United States develop

lactose intolerance, a disorder that results from a defi-

ciency of the enzyme lactase. It prevents normal digestion

and absorption of lactose, the sugar found in milk and many

milk products. Nausea, cramps, bloating, and diarrhea are

common symptoms. People who have celiac disease, or

gluten intolerance, are hypersensitive to gluten, a form

of protein in wheat, rye, and barley. The disorder involves

an autoimmune response in

which lymphocytes attack

the villi of brush border

cells. Symptoms can range

from lethargy and rashes

to joint pain, mouth sores,

and osteoporosis. People

with gluten intolerance can

control their symptoms by

eating a gluten-free diet.

Other malabsorption disorders are associated with dis-

eases that affect the pancreas, including the genetic condi-

tion cystic fibrosis (cF). Patients with CF don’t make the

necessary pancreatic enzymes for normal digestion and

absorption of fats and other nutrients. CF also affects the

lungs, as you will read in later chapters.

descending colon

transverse colon

colon polyps

Figure 11.17 a polyp on the colon wall may be a precursor to

colorectal cancer. The sketch shows one site where a colon

polyp might be found—here, in the transverse colon. The photo

shows a polyp found during a colonoscopy. Suspicious polyps

can be removed and examined for the presence of cancer.

Figure 11.16 crohn’s disease can do severe intestinal harm.
The blotchy areas in this X-ray image are ulcers in the wall of
the intestine.

CNRI/Science Source

Science Source

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