Chemoreceptor Trigger Zone

The fifty-eight year old lady mentioned in the case history is diagnosed with skin cancer. She has been referred for a chemotherapy session and is informed by the oncologist of the side effects; nausea and vomiting. Vomiting also referred to as emesis in medical terms ‘is the forceful expulsion of the contents of the gastrointestinal system out through the mouth’ (Virtual medical centre, 2005). It is the symptoms of many different conditions and the side effects of certain drugs. Vomiting is the response of an activated emetic reflex by the integrative vomiting centre. The initiation of an emetic response can be prevented by the use anti-emetics drugs. These drugs are often useful for patients that are undergoing chemotherapy. The drugs act
The chemoreceptor trigger zone is situated on the floor of the fourth ventricle of the brain within the area postrema (Bowen, R., 1996). It consists of a blood-brain barrier that is able to detect chemical stimuli within the blood and the cerebrospinal fluid. The chemoreceptors which are situated within the chemoreceptor trigger zone are stimulated by many drugs and toxic substances; referred to as emetics (Sherwood, L., 2013). When emetics cause a stimulation of the chemoreceptor trigger zone, impulses are relayed across the to the integrative vomiting centre, causing an initiation of the emetic reflex. Therefore it is not merely the chemoreceptor trigger zone that stimulates the vomiting itself, but the integrative vomiting centre that results in the act of emesis (Rang, H.P., et al,
Any unpleasant sight, smell and taste can result in the activation of the higher centres in the brain. The higher centres of the brain then relay impulses to the integrative vomiting centre activating the emetic response. In addition infections of the labyrinth can lead to motion sickness. The vestibular nerve is stimulated by the infection, leading to the transmission of impulses that activate the chemoreceptor trigger zone (Virtual medical centre, 2005).
The emetic reflex mechanism is categorised into two phases: a retching phase and the expulsive phase. The retching phase occurs first, and involves the contraction of the abdominal muscles, chest wall and diaphragm. The sustained contraction of the diaphragm, chest wall and abdominal muscle leads to a build-up of increased pressure within the stomach. The release of this pressure is characterised as the expulsive phase, and this is what results in the expulsion of the contents of the stomach (Virtual medical centre,