Encyclopedia of Health and Medicine

94 The Gastrointestinal System
the DUODENUM (first section of the SMALL INTESTINE).
Like sneezing and coughing, vomiting is a protective
and reflexive mechanism to rid the body of
substances that threaten its well-being.
Vomiting occurs in response to NERVE impulses
from the BRAIN’s emesis center (also called vomiting
center). The emesis center receives input from
numerous body systems, including the gastrointestinal
tract, vestibular system (which regulates
balance), and circulatory system, as well as from
the chemoreceptor trigger zone, another region of
the brain that receives signals from the body. PAIN
signals, particularly those the vagus nerve conveys,
also travel to the emesis center, which is
why severe pain may result in NAUSEA (queasiness
and the feeling of being about to vomit) and vomiting.
Other variables that influence the emesis center
include sensory perceptions such as foul smells or
disturbing sights (which activate the chemoreceptor
zone), hormonal shifts (such as occur in pregnancy
to cause MORNING SICKNESS), and signals
from the gastrointestinal tract indicating chemical
changes such as from the presence of INFECTION or
INFLAMMATION. Nausea, the sensation of queasiness
and the urge to vomit, typically though not always
precedes vomiting.
A complex series of physiologic events takes
place to permit vomiting. Simultaneously the
epiglottis closes (blocking the airway), the larynx
lifts, and the upper esophageal sphincter opens.
Then the DIAPHRAGM violently contracts, pulling it
down and causing the open the lower esophageal
sphincter to open, while the abdominal muscles
contract with comparable force to push gastric
(stomach) contents upward through the now
open esophagus. Vomitus is highly acidic; chronic
vomiting such as occurs with anorexia nervosa
causes erosion of the tooth enamel. This material
has a bitter taste and often leaves a burning sensation
in the upper THROAT. Though the mechanism
of vomiting is involuntary, there is some voluntary
control over its initiation.
Episodic vomiting generally has no lasting consequences,
though the very young and the very
old can quickly become dehydrated. Vomiting that
continues longer than three or four weeks without
apparent cause requires medical evaluation.
Treatment may include ANTIEMETIC MEDICATIONS,
dietary changes, or therapies to resolve underlying
conditions. Complications of chronic or repeated
vomiting may include ESOPHAGITIS, electrolyte
imbalance, and ASPIRATION PNEUMONIA.
See also COUGH; CYCLIC VOMITING SYNDROME; DEHY-
DRATION; EATING DISORDERS; FOOD-BORNE ILLNESSES;
LABYRINTHITIS; MÉNIÈRE’S DISEASE; SNEEZE.
Whipple’s disease A bacterial INFECTION of the
SMALL INTESTINE, also called intestinal lipodystrophy,
that impairs absorption of fats (lipids). The
PATHOGEN (infective BACTERIA) is Tropheryma whippelii.
Though T. whippelii can infect various body
systems including the HEART and the EYE, the gastrointestinal
tract is its most common site. In the
small intestine the bacteria create lesions (disruptions
in the continuity of the intestinal mucosa)
that destroy the villi, the microscopic, fingerlike
extensions of tissue where much of the intestine’s
absorption functions take place. Researchers do
not know how people acquire T. whippelii, though
do know the infection can take years to decades to
manifest symptoms.
Symptoms include DIARRHEA, GASTROINTESTINAL
BLEEDING, OSTEOARTHRITIS, MALNUTRITION, unintended
weight loss, HEADACHE, and FEVER. The diagnostic
path may include general blood tests, BARIUM
SWALLOW with small intestine flow-through, and
ENDOSCOPY with biopsy to culture a tissue sample
from the inner intestine. Treatment is a course of
intravenous ANTIBIOTIC MEDICATIONS, typically penicillin
and streptomycin or chloramphenicol in
combination, with 12 to 18 months of oral antibiotic
therapy to completely eradicate the bacteria.
See also GASTROENTERITIS; MALABSORPTION.
Zollinger-Ellison syndrome A rare disorder in
which the STOMACH dramatically increases
hydrochloric acid production, resulting in rampant
PEPTIC ULCER DISEASE. Zollinger-Ellison syndrome
develops as a consequence of benign tumors,
called gastrinomas, that secrete the digestive HOR-
MONE gastrin. Gastrin signals the stomach to produce
acid, which the stomach continues doing as
long as gastrin remains present. The excess acid
that results causes extreme irritation of the gastric
mucosa (stomach’s lining), leading to numerous
ulcers. The gastrinomas may form in the PANCREAS
or the DUODENUM (first segment of SMALL INTESTINE).