vomiting is basic human protective reflexes against the absorption of toxins, as well as responses to certain stimuli. Vomiting is characterized by contraction of the abdominal muscles, descent of the diaphragm, and opening of the gastric cardia, resulting in forceful expulsion of stomach contents from the mouth.1 Retching involves spasmodic contractions of the diaphragm and the muscles of the thorax and abdominal wall without expulsion of gastric contents, the so-called dry heaves.

Mekanisme : The activation of a nucleus of neurons located in the medulla oblongata, known as the vomiting center, initiates the vomiting reflex. The vomiting center can be activated directly by signals from the cerebral cortex (anticipation, fear, memory), signals from sensory organs (disturbing sights, smells, pain), or signals from the vestibular apparatus of the inner ear (motion sickness). The vomiting center can also be activated indirectly by certain stimuli that activate the chemoreceptor trigger zone (CTZ)3.The CTZ is located in the highly vascular area postrema on the surface of the brain. This area lacks a true blood-brain barrier and is exposed to both blood and cerebrospinal fluid; thus, the CTZ can react directly to substa nces in the blood.2 The CTZ can be activated by signals from the stomach and small intestine traveling along vagal afferent nerves or by the direct action of emetogenic compounds that are carried in the blood (anti-cancer drugs, opioids, ipecac).

Specific neurotransmitters and neuromodulators in the CTZ identify substances as potentially harmful and relay impulses to the vomiting center to initiate the vomiting cascade so that the harmful substance can be expelled. These neurotransmitters are serotonin, dopamine, acetylcholine (muscarinic cholinergic), and histamine. A fifth chemoreceptor, the neurokinin-1 neuropeptide, also called substance P, is currently under study.4,5

Stimulation of these chemoreceptors triggers activation of the vomiting center. Therefore, any interference with the transmission of these chemoreceptors prevents the vomiting center from being activated. Many antiemetics act by blocking 1 or more of these receptors.3 Dopamine antagonists block dopamine receptors; muscarinic antagonists block acetylcholine receptors; histamine blockers block histamine receptors; and serotonin receptor blockers block serotonin receptors. The adverse effects of these drugs are also determined by which receptor site is blocked

TYPES OF VOMITING

Vomiting can be classified according to its nature and cause as well as by the character of the vomitus. The nature of the vomiting may be projectile or nonprojectile. Projectile vomiting refers to forceful vomiting and may indicate increased intracranial pressure, especially if it occurs early in the morning. Projectile vomiting also is a classic feature of pyloric stenosis. Nonprojectile vomiting is seen more commonly in gastroesophageal reflux. These somewhat arbitrary descriptions are not definitive in establishing a diagnosis.Emesis often is classified based on its quality. The vomitus may be bilious, bloody, or nonbloody and nonbilious. Emesis originating from the stomach usually is characterized as being clear or yellow and often contains remnants of previously ingested food. Emesis that is dark green is referred to as bilious because it indicates the presence of bile. Bilious vomiting frequently is pathologic because it may be a sign of an underlying abdominal problem such as intestinal obstruction beyond the duodenal ampulla of Vater, where the common bile duct empties. The presence of blood in the emesis, also known as hematemesis, indicates acute bleeding from the upper portion of the GI tract, as can occur with gastritis, Mallory-Weiss tears, or peptic ulcer disease. Coffee ground-like material often is representative of an old GI hemorrhage because

blood darkens to a black or dark-brown color when exposed to the acidity of the gastric secretions. The more massive or proximal the bleeding, the more likely it is to be bright red.