Activation Of Chemoreceptor Trigger Zone

Area Postrema: Chemoreceptor Trigger Zone for Vomiting a crucial role as a chemoreceptor trigger zone for of AP as a chemosensitive trigger zone.

The chemoreceptor trigger zone The activation of these opioid receptors in the CTZ are especially important for patients who take opioid based pain medications.

Vomiting is the forceful expulsion of contents of the stomach and often, the proximal small intestine. It is a manifestation of a large number of conditions, many of which are not primary disorders of the gastrointestinal tract. Regardless of cause, vomiting can have serious consequences, including acid-base derangments, volume and electrolyte depletion, malnutrition and aspiration pneumonia.

The Act of Vomiting

Vomiting is usually experienced as the finale in a series of three events, which everyone reading this has experienced:

Nausea is an unpleasant and difficult to describe psychic experience in humans and probably animals. Physiologically, nausea is typically associated with decreased gastric motility and increased tone in the small intestine. Additionally, there is often reverse peristalsis in the proximal small intestine.

Retching dry heaves refers to spasmodic respiratory movements conducted with a closed glottis. While this is occurring, the antrum of the stomach contracts and the fundus and cardia relax. Studies with cats have shown that during retching there is repeated herniation of the abdominal esophagus and cardia into the thoracic cavity due to the negative pressure engendered by inspiratory efforts with a closed glottis.

Emesis or vomition is when gastric and often small intestinal contents are propelled up to and out of the mouth. It results from a highly coordinated series of events that could be described as the following series of steps don t practice these in public :

A deep breath is taken, the glottis is closed and the larynx is raised to open the upper esophageal sphincter. Also, the soft palate is elevated to close off the posterior nares.

The diaphragm is contracted sharply downward to create negative pressure in the thorax, which facilitates opening of the esophagus and distal esophageal sphincter.

Simultaneously with downward movement of the diaphragm, the muscles of the abdominal walls are vigorously contracted, squeezing the stomach and thus elevating intragastric pressure. With the pylorus closed and the esophagus relatively open, the route of exit is clear.

The series of events described seems to be typical for humans and many animals, but is not inevitable. Vomition occasionally occurs abruptly and in the absense of premonitory signs - this situation is often referred to as projectile vomiting. A common cause of projectile vomiting is gastric outlet obstruction, often a result of the ingestion of foreign bodies.

An activity related to but clearly distinct from vomiting is regurgitation, which is the passive expulsion of ingested material out of the mouth - this often occurs even before the ingesta has reached the stomach and is usually a result of esophageal disease. Regurgitation also is a normal component of digestion in ruminants.

There is also considerable variability among species in the propensity for vomition. Rats reportedly do not vomit. Cattle and horses vomit rarely - this is usually an ominous sign and most frequently a result of acute gastric distension. Carnivores such as dogs and cats vomit frequently, often in response to such trivial stimuli as finding themselves on a clean carpet. Humans fall between these extremes, and interestingly, rare individuals have been identified that seem to be incapable of vomiting due to congenital abnormalities in the vomition centers of the brainstem.

Control of Vomition

The complex, almost sterotypical set of activities that culminate in vomiting suggest that control is central, which indeed has been shown to be true. Within the brainstem are two anatomically and functionally distinct units that control vomiting:

Bilateral vomition centers in the reticular formation of the medulla integrate signals from a large number of outlying sources and their excitement is ultimately what triggers vomition. Electric stimulation of these centers induces vomiting, while destruction of the vomition centers renders animals very resistant to emetic drugs. The vomition centers receive afferent signals from at least four major sources:

The chemoreceptor trigger zone see below

Visceral afferents from the gastrointestinal tract vagus or sympathetic nerves - these signals inform the brain of such conditions as gastrointestinal distention a very potent stimulus for vomition and mucosal irritation.

Visceral afferents from outside the gastrointestinal tract - this includes signals from bile ducts, peritoneum, heart and a variety of other organs. These inputs to the vomition center help explain how, for example, a stone in the common bile duct can result in vomiting.

Afferents from extramedullary centers in the brain - it is clear that certain psychic stimuli odors, fear, vestibular disturbances motion sickness and cerebral trauma can result in vomition.

The chemoreceptor trigger zone is a bilateral set of centers in the brainstem lying under the floor of the fourth ventricle. Electrical stimulation of these centers does not induce vomiting, but application of emetic drugs does - if and only if the vomition centers are intact. The chemoreceptor trigger zones function as emetic chemoreceptors for the vomition centers - chemical abnormalities in the body e.g. emetic drugs, uremia, hypoxia and diabetic ketoacidosis are sensed by these centers, which then send excitatory signs to the vomition centers. Many of the antiemetic drugs act at the level of the chemoreceptor trigger zone.

To summarize, two basic sets of pathways - one neural and one humoral - lead to activation of centers in the brain that initiate and control vomition. Think of the vomition centers as commander in chief of vomition, who makes the ultimate decision. This decision is based on input from a battery of advisors, among whom the chemoreceptor trigger zone has considerable influence. This straighforward picture is almost certainly oversimplified and flawed in some details, but helps to explain much of the physiology and pharmacology of vomition.

Causes and Consequences of Vomiting

The myriad causes of vomiting are left as an exercise - come up with a list based on personal experience and your understanding of the control of vomition. An important point, however, is that many cases of vomiting are due to diseases outside of the gastrointestinal tract.

Simple vomiting rarely causes problems, but on occasion, can lead to such serious consequences as aspiration pneumonia. Additionally, severe or repetitive vomition results in disturbances in acid-base balance, dehydration and electrolyte depletion. In such cases, the goal is to rapidly establish a definitive diagnosis of the underlying disease so that specific therapy can be instituted. This is often not easy and in many cases, it is advantageous to administer antiemetic drugs in order to suppress vomition and reduce its sequelae.

Looking for online definition of chemoreceptor trigger zone Activation stimulates neurons of the emetic center. chemoreceptor cell; Chemoreceptor trigger zone;.

The area postrema and vomiting. has been implicated as a chemoreceptor trigger zone for vomiting induced by motion or by activation of vagal nerve.

Physiology of Vomiting

Apr 10, 1996  Physiology of Vomiting: The chemoreceptor trigger zone lead to activation of centers in the brain that initiate and control vomition.

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chemoreceptor  ke mo-re-sep ter

any of the special cells or organs adapted for excitation by chemical substances and located outside the central nervous system. The carotid and aortic bodies are chemoreceptors in the large arteries of the thorax and the neck; they are responsive to changes in the oxygen, carbon dioxide, and hydrogen ion concentrations in the blood. When oxygen concentration falls below normal in the arterial blood, they send impulses to stimulate the respiratory center so that there will be an increase in alveolar ventilation and thus an increase in the intake of oxygen by the lungs. Other chemoreceptors are the taste buds, which are sensitive to chemicals in the mouth, and the olfactory cells of the nose, which detect certain chemicals in the air.che mo re cep tor kē mō-rē-sep tŏr,

Any cell that when activated by a change in its chemical milieu produces a nerve impulse. Such cells can be either 1 transducer cells innervated by sensory nerve fibers for example, the gustatory receptor cells of the taste buds or cells in the carotid body sensitive to changes in the oxygen and carbon dioxide content of the blood, or 2 nerve cells proper, such as the olfactory receptor cells of the olfactory mucosa, and certain cells in the brainstem that are sensitive to changes in the composition of the blood or cerebrospinal fluid.chemoreceptor /che mo re cep tor/ -re-sep ter a receptor sensitive to stimulation by chemical substances.che mo re cep tor kē mō-rĭ-sĕp tər n.

A sensory nerve cell or sense organ, as of smell or taste, that responds to chemical stimuli.chemoreceptor -risep tər

Etymology: Gk, chemeia L, recipere, to receive

a sensory nerve cell activated by chemical stimuli. For example, chemoreceptors in the carotid artery are sensitive to the partial pressure of carbon dioxide in the blood; they signal the respiratory center in the brain to increase or decrease the rate of breathing. che mo re cep tor, chemoceptor kē mō-rĕ-sep tŏr, kēmō-septŏr

Any cell that responds to a change in its chemical milieu with a nerve impulse. Such cells can be either transducer cells innervated by sensory nerve fibers e.g., the gustatory cells of the taste buds or nerve cells proper, such as the olfactory receptor cells of the olfactory mucosa. che mo re cep tor, chemoceptor kē mō-rĕ-sep tŏr, kēmō-septŏr

Any cell that responds to a change in its chemical milieu with a nerve impulse. chemoreceptor kē mōrēsep tər,

n a specialized sensory end organ adapted for excitation by chemical substances e.g., olfactory and gustatory receptors or specialized sense organs of the carotid body that are sensitive to chemical changes in the bloodstream.chemoreceptor

any of the special cells or organs adapted for excitation by chemical substances and located outside the central nervous system. There are chemoreceptors in the large arteries of the thorax and the neck; called carotid and aortic bodies. These receptors are responsive to changes in the oxygen, carbon dioxide and hydrogen ion concentration in the blood. When oxygen concentration falls below normal in the arterial blood, the chemoreceptors send impulses to stimulate the respiratory center so that there will be an increase in alveolar ventilation, and consequently, an increase in the intake of oxygen by the lungs.

Other chemoreceptors are the taste buds, which are sensitive to chemicals in the mouth, and the olfactory cells of the nose, which detect certain chemicals in the air.chemoreceptor trigger zone CTZ

located in the floor of the fourth ventricle; sensitive to motion, uremia, apomorphine. Activation stimulates neurons of the emetic center.chemoreceptor tumors

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