Chemoreceptor Trigger Zone : Emesis originates by several physiologic mechanisms that respond to stimulation of the central and peripheral nervous systems, the effect (vomiting) is the result of a series of motor activities in the chest and abdomen. The final motor co-ordination that results in vomiting occurs because of the stimulation of the emetic centre, an area of the brainstem, which is vested in two separate units of the medulla: the chemoreceptor trigger zone (CTZ) and the vomiting centre (VC). Enterochromaffin cells in the gut are one of the bodys largest reservoirs of the neurotransmitter serotonin. When enterochromaffin cells are damaged or destroyed they release serotonin (5-hydroxytryptamine or 5-HT), which then binds with serotonin type 3 (5-HT3) receptors located on vagal afferent nerves, causing stimulatory impulses to the emetic centre. As a secondary emetic pathway, serotonin released in the gastrointestinal tract may also travel via the bloodstream to the brain and activate central 5-HT3 receptors in the chemoreceptor trigger zone. Recent studies point to the importance of the exposure of the CTZ to a variety of neurotransmitters (i.e., neuroreceptors in the gastrointestinal tract which have afferents to the vomiting centre) that are known as mediators of nausea and vomiting, including serotonin, dopamine, histamine, prostaglandins, and gamma-aminobutyric acid. The vomiting centre receives many excitatory inputs from nerve endings of vagal sensory fibres in the gastrointestinal tract, from the labyrinths via the vestibular nuclei, from higher centres in the cortex, from the CTZ, and from intracranial pressure receptors. Chemotherapeutic agents are toxins by their nature and mechanism of action; they can induce local cellular toxicity in the stomach cells, which stimulates the release of serotonin. Serotonin causes emesis by either stimulating afferent fibers directly or by passing into the circulation and stimulating the emetic centers. Chemotherapeutic agents vary significantly in their emetogenic potential (their ability to cause emesis) from low to high.
Posted on: Mon, 14 Jul 2014 18:45:19 +0000
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