Dry heavesare not the same as nausea. Dry heavesis a term that is used to refer to the nauseathat occurs much after repeated rounds of nauseahave emptied the stomach of contents, and the nauseous feeling continues and further results in vomitingor emesis.
Nauseais a condition in which one feels uneasy, especially in the stomach. This is usually followed by the expulsion of the contents of the stomach. The act of vomitingitself starts with the activation of certain receptors in the brain that are stimulated. This starts a chain reaction to other parts of the body. The first signals go the salivary glands in the back of the mouth to start secreting acid. This is a protective mechanism by the body to ensure that the teeth do not get affected by the acids of the stomach. The next stage in emesis is a reverse peristalsis movement that occurs. This starts all the way down in the small intestine and pushes up all the material from that point upwards. There is then a sudden reflex to take a deep breath. This is also a body mechanism to avoid breathing in material, when emesis does take place. The sphincters of the stomach, namely the pyloric and esophageal, open up and the differences in pressure then causethe food to rise into the esophagus and then out from the oral cavity.
Curiously, in some people, especially those who suffer from diseases of dysphagia like Achalasia, the nauseousfeeling and subsequent vomiting is causedby an accumulation of food in the esophagus itself; therefore, the usual mechanisms of vomitingdo not occur and expulsion of food is something that cannot be even anticipated.
The causes of vomitingcan be placed squarely on three reasons: a problem in the stomach, a problem in the brain, or the effect of drugs. The stomach will usually be the cause of problems, when food that is not supposed to be ingested has been consumed, a natural reflex or the presence of toxins is detected, and contents are expelled. The brain also contributes when there is too much intracranial pressure that has built up squeezing the brain tissue. The body will deal with this problem by trying to forcible dehydrate itself, or this is a reaction that happens when a receptor is affected. Dry heaves are usually and indication of a problem with intracranial pressure and should never be ignored.