MOUTH, STOMACH, and SMALL INTESTINEto assist in
absorbing NUTRIENTSfrom foods. Gastrointestinal
structures produce dozens of digestive enzymes,
which they secrete in various digestive juices.
Amylase in saliva, for example, breaks down car-
bohydrates into their sugar components. Gastric
juices combine acid and protease (pepsin) to fur-
ther hydrolyze foods. Numerous enzymes in the
small intestine—such as lactase, cellulase, lipase,
maltase—facilitate the chemical changes necessary
to convert food particles to nutrient molecules the
intestinal mucosa can absorb and transport into
the bloodstream. Shortages of enzymes may occur,
naturally or due to health conditions, that result
in gastrointestinal disorders. A shortage of lactase,
for example, causes LACTOSE INTOLERANCE.
See also CARBOHYDRATE INTOLERANCE; DIGESTIVE
HORMONES; NUTRITIONAL SUPPLEMENTS.
digestive hormones Chemical messengers that
stimulate or inhibit gastrointestinal functions.
Organs and structures of the gastrointestinal sys-
tem synthesize and release digestive hormones in
response to chemical and physiologic changes that
take place with the ingestion of food and its pas-
sage through the gastrointestinal tract. The major
digestive hormones are
- gastrin, which stimulates the STOMACHto release
gastric juices and begin contracting - cholecystokinin (CCK), which stimulates the
GALLBLADDER to release BILE, the PANCREAS to
release digestive juices, and the stomach to
slow the release of chyme (the slushy mix of
food and digestive secretions) into the DUODE-
NUM(first segment of the SMALL INTESTINE) - secretin, which accelerates bile release from the
gallbladder, stimulates the pancreas to release
bicarbonates to neutralize stomach acid, and
slows the release of gastric juices as chyme
advances from the stomach into the duodenum - motilin, which stimulates PERISTALSIS(contrac-
tions of the gastrointestinal tract) - gastric inhibitory polypeptide (GIP), which
stimulates the pancreas to release INSULIN, slows
(inhibits) the release of gastric juices, and slows
stomach contractions- enterogastrone, which stimulates the stomach
to release chyme into the duodenum - vasoactive intestinal peptide (VIP), which stops
the production of gastric acid - SOMATOSTATIN, which stops the release of insulin
and further slows gastric motility (the stom-
ach’s contractions)
- enterogastrone, which stimulates the stomach
See also DIABETES; DIGESTIVE ENZYMES; HORMONE.digital rectal examination (DRE) Direct palpa-
tion of the RECTUMin which the doctor inserts a
gloved and lubricated finger into the rectum via
the ANUS. DRE allows the doctor to feel for abnor-
mal growths within the rectum and, in men, to
palpate the PROSTATE GLANDfor enlargement and
possibly nodules that could suggest PROSTATE CAN-
CER. The doctor can perform DRE as an office pro-
cedure; there is little discomfort. The person may
lie on his or her side with knees drawn up. DRE
may accompany a PELVIC EXAMINATIONfor a woman.
DRE is also part of the examination to determine
the cause of acute ABDOMINAL PAINand other symp-
toms of health conditions affecting the lower gas-
trointestinal tract.
See also BENIGN PROSTATIC HYPERPLASIA(BPH); CAN-
CER PREVENTION.diverticular disease A chronic condition in
which pockets of the gastrointestinal mucosa
(inner lining of the intestines) bulge through
weakened areas of the intestinal wall, forming
HERNIA-like protrusions called diverticula. Divertic-
ula may form anywhere along the gastrointestinal
tract from the ESOPHAGUSto the RECTUM, though
are most common in the sigmoid COLON. Most
diverticular disease develops over decades and
manifests symptoms after age 60. A congenital
form of diverticular disease, Meckel’s diverticu-
lum, affects the SMALL INTESTINE, typically the
ILEUM. Meckel’s diverticulum is uncommon. Diver-
ticulosis is the presence of multiple diverticula;
diverticulitis occurs when diverticula become
inflamed or infected. Doctors suspect diverticular
disease results from changes in the gastrointestinal
system that occur with aging. Though for some
people the condition is debilitating, many people
who have diverticular disease have few symp-diverticular disease 35