The duodenum releases secretin, which is a hormone that suppresses gastric
acid secretion. This results in the intestinal juices having a higher pH than the
gastric juices in the stomach. The hormone cholecystokinin is also released. It
simulates the flow of bile into the duodenum. Hormones, bile, and pancreatic
enzymes trypsin, chymotrypsin, lipase, and amylase digest carbohydrates, pro-
tein, and fat in preparation for absorption in the small intestine.
The small intestine lead into the large intestine where undigested material
from the small intestine is collected. The large intestine also absorbs water and
secretes mucus while moving the undigested material—using peristaltic con-
tractions—to the rectum where it is eliminated through defecation.
VOMITING
Vomiting (emesis) is the expulsion of gastric contents of the stomach through the
esophagus and out the oral cavity. Vomiting is sometimes preceded by nausea,
which is a queasy sensation, although vomiting can occur without nausea. Vomiting
can occur for a number of reasons. These include motion sickness, viral and bacte-
rial infections, food intolerance, surgery, pregnancy, pain, shock, effects of selected
drugs, radiation, and disturbances of the middle ear affecting equilibrium.
Vomiting occurs when two major centers in the cerebrum are stimulated.
These are the chemoreceptor trigger zone (CTZ) that lies near the medulla and
the vomiting center in the medulla. The CTZ receives impulses from drugs, tox-
ins, and the vestibular center in the ear. These impulses are transmitted by the
neurotransmitter dopamine to the vomiting center. The neurotransmitter acetyl-
choline is also a vomiting stimulant. Sensory impulses such as odor, smell, taste,
and gastric mucosal irritation are transmitted directly to the vomiting center.
When the vomiting center is stimulated, motor neurons respond causing con-
traction of the diaphragm, the anterior abdominal muscles, and the stomach. The
glottis closes, the abdominal wall moves upward, and the stomach contents are
forced up the esophagus.
When vomiting occurs, try to identify the cause before treating the patient.
Begin treatment with nonpharmacological measures such as drinking weak tea,
flattened carbonated beverages, gelatin, Gatorade, and for children, Pedialyte.
Crackers and dry toast may also be helpful.
Nausea and vomiting that occur during the first trimester of pregnancy should
be treated with nonpharmacologic remedies since amtimetics can cause possible
harm to the fetus.
If dehydration occurs because vomiting is severe, intravenous fluids may be
needed to restore body fluid balance.
CHAPTER 18 Gastrointestinal System^331