Vomiting
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| image credit by-Estrada Anton |
It can be defined as the process by which the contents of the upper gut are expelled to the exterior through the mouth. In most of the cases the unwanted and irritating materials are got rid of by this process. Vomiting is associated with serious diseases like appendicitis, cholecystitis, gastritis, acute myocardial infarction, and in cases of increased intracranial tension. Vomiting also occurs due to psychological reasons, motion sickness, etc.
The act of vomiting is integrated at the vomiting centre in the brainstem reticular formation situated near the salivary centre: that is why vomiting is usually associated with salivation. There is another area called chemo-receptor trigger zone (CTZ) situated in the area postrema near the vomiting centre; if the CTZ is stimulated by morphine like drugs or by various metabolites as in uraemia, and in other conditions, then the CTZ stimulates the vomiting centre and vomiting occurs. Many drugs which prevent vomiting do so by inhibiting this CTZ.
For vomiting to occur different stimuli which cause Vomiting converge to the vomiting centre and then vomiting occurs along with simultaneous arrest of respiration. In the process there is contraction of the diaphragm and anterior abdominal wall. This raises the intra-abdominal pressure. There is relaxation of the cardiac end of the stomach along with antiperistalsis and the stomach contents are ejected out by the high intra-abdominal pressure. During the process, the larynx and nasopharynx are closed; therefore the vomitus can neither go inside the nose nor can enter in the respiratory tract.
Excessive vomiting is always harmful. It causes
loss of Tluid and electrolytes particularly of H" and K", and the
person may suffer from alkalosis and hypokalaemia. Vomiting also Occurs in the
early months of pregnancy. Nausea is a sensation which usually precedes
vomiting but nausea is not always followed by vomiting.