C h a p t e r 2 9
Disorders of Gastrointestinal Function
713
the lower right quadrant, which is confined to a small
area approximately the size of the fingertip. It usually is
located at approximately the site of the inflamed appen-
dix. The person with appendicitis often is able to place
his or her finger directly over the tender area. Rebound
tenderness, which is pain that occurs when pressure is
applied to the area and then released, and spasm of the
overlying abdominal muscles are common.
Diagnosis is usually based on history and findings on
physical examination. Ultrasonography or CT may be
used to confirm the diagnosis.
41
Treatment consists of
surgical removal of the appendix. Complications include
peritonitis, localized periappendiceal abscess formation,
and septicemia.
Disorders of Intestinal Motility
Intestinal motility, or the movement of contents
through the gastrointestinal tract, is controlled by neu-
rons located in the submucosal and myenteric plexuses
of the gut (see Chapter 28). The axons from the cell
bodies in the myenteric plexus innervate the circular
and longitudinal smooth muscle layers of the gut. These
neurons receive impulses from local receptors located in
the mucosal and muscle layers of the gut and extrinsic
input from the parasympathetic and sympathetic ner-
vous systems. As a general rule, the parasympathetic
nervous system tends to increase the motility of the
bowel, whereas sympathetic stimulation tends to slow
its activity.
The large intestine has sphincters at both ends: the
ileocecal sphincter, which separates it from the small
intestine; and the anal sphincter, which prevents the
movement of feces to the outside of the body. About
1500 mL of fluid and undigested food normally pass
through the ileocecal valve into the large intestine each
day. Most of the water and electrolytes in the fluid are
absorbed in the colon, usually leaving less than 100 mL
to be excreted in the feces.
2
The large intestine can
absorb a maximum of 5 to 8 L of fluid and electrolytes
each day. When the total amount entering the large
intestine through the ileocecal valve or by way of intes-
tinal secretion exceeds this amount, the excess appears
in the feces as diarrhea.
Diarrhea
The usual definition of
diarrhea
is excessively frequent
passage of stools. Diarrhea can be acute or chronic and
can be caused by infectious organisms, food intoler-
ance, drugs, or intestinal disease. In developing coun-
tries, diarrhea is a common cause of mortality among
children younger than 5 years of age, with an estimated
2 million deaths annually.
42
Even though diarrheal dis-
eases are less prevalent in the United States than in other
countries, they place a burden on the health care system.
Acute Diarrhea.
Acute diarrhea is predominantly
caused by infectious agents and follows a self-limited
course of less than 2 weeks.
43
Acute diarrhea is com-
monly divided into noninflammatory (large-volume)
and inflammatory (small-volume) diarrhea, based on
the characteristics of the diarrheal stool. Enteric organ-
isms cause diarrhea in several ways. Some organisms are
noninvasive and do not cause inflammation, but secrete
toxins that stimulate fluid secretion.
44,45
Others invade
and destroy intestinal epithelial cells, thereby altering
fluid transport so that secretory activity continues while
absorption activity is halted.
Noninflammatory diarrhea
is associated with
large-volume watery and nonbloody stools, perium-
bilical cramps, bloating, and nausea or vomiting. It is
commonly caused by toxin-producing bacteria (e.g.,
enterotoxigenic
E. coli, S. aureus, Vibrio cholerae
) or
other agents (e.g., viruses,
Giardia
) that disrupt the
normal absorption or secretory process in the small
bowel. Prominent vomiting suggests viral enteritis or
S. aureus
food poisoning.
32
Although typically mild,
diarrhea that originates in the small intestine can be
voluminous and result in dehydration with hypoka-
lemia and metabolic acidosis. Because tissue invasion
and inflammation do not occur, leukocytes are not
present in the feces.
Inflammatory diarrhea
is usually characterized by
the presence of fever and bloody diarrhea. It is caused
by bacterial invasion of intestinal cells (e.g.,
Shigella,
Salmonella
,
Yersinia
, and
Campylobacter
) or the toxins
associated with the previously described
C. difficile
or
E. coli
O157:H7 infection. Because infections associated
with these organisms predominantly affect the colon,
the diarrhea is small in volume (<1 L/day) and is associ-
ated with lower abdominal pain and the urgent desire
to defecate. Infectious dysentery must be distinguished
from acute ulcerative colitis, which may present with
bloody diarrhea, fever, and abdominal pain. Diarrhea
that persists for 14 days is usually not caused by bacte-
rial pathogens (except for
C. difficile
), and the person
should be evaluated for chronic diarrhea.
Chronic Diarrhea.
Diarrhea is considered to be chronic
when the symptoms persist for 3 to 4 weeks in children
or adults and 4 weeks in infants. Chronic diarrhea is
often associated with conditions such as irritable bowel
and inflammatory bowel syndromes, malabsorption dis-
orders, endocrine disorders (hyperthyroidism, diabetic
autonomic neuropathy), or radiation colitis. There are
four major causes of chronic diarrhea: presence of hyper-
osmotic luminal contents, increased intestinal secretory
processes, inflammatory conditions, and infectious
processes
8
(Chart 29-1). A condition called
factitious
diarrhea
is caused by indiscriminate use of laxatives or
excessive intake of laxative-type foods.
In
osmotic diarrhea,
water is pulled into the bowel by
the hyperosmotic nature of its luminal contents. It occurs
when osmotically active particles are not absorbed. In
persons with lactase deficiency, the lactose in milk can-
not be broken down and absorbed. Magnesium salts,
which are contained in milk of magnesia and many
antacids, are poorly absorbed and cause diarrhea when
taken in sufficient quantities. Another cause of osmotic
diarrhea is decreased transit time, which interferes with
absorption.
