The mouth often fills with saliva just before vomiting. This phenomenon, known as hypersalivation, is a coordinated physiological response aimed at protecting the body. The body anticipates the forceful expulsion of stomach contents and prepares itself through a series of reflexes involving the nervous system and various bodily functions.
The Protective Function of Saliva
The increased production of saliva before vomiting serves a protective role. Stomach acid is highly corrosive, with a typical pH ranging from 1.5 to 3.5. Exposure to this strong acid can damage tooth enamel, the lining of the esophagus, and the oral cavity. Saliva, which is typically slightly alkaline with a pH between 6.0 and 7.4, acts as a natural buffer. The surge in salivary flow, especially stimulated saliva, increases its bicarbonate concentration, which helps neutralize the stomach acid.
This buffering action helps to reduce the acidity of the vomit as it passes through the esophagus and mouth, thereby minimizing potential damage to these structures. Saliva also lubricates the passage, making the expulsion process less abrasive. Additionally, it helps to rinse away any lingering acid from the teeth and oral tissues after vomiting, further safeguarding them from erosion.
The Brain’s Anticipatory Response
The surge in salivation before vomiting is orchestrated by the brain, specifically the medulla oblongata, often referred to as the “vomiting center.” This center receives signals from various parts of the body, indicating potential threats that could lead to vomiting. These signals can originate from the chemoreceptor trigger zone (CTZ), which monitors the blood for toxins, or from the gastrointestinal tract, and even higher brain centers due to psychological triggers like unpleasant sights or smells.
Once activated, the medulla oblongata sends signals through the autonomic nervous system, particularly its parasympathetic branch, to the salivary glands. The parasympathetic nervous system is responsible for “rest and digest” functions, including stimulating saliva production. This neurological pathway ensures that saliva is produced rapidly in anticipation of vomiting, preparing the oral cavity and esophagus for the acidic contents. This coordinated response is an involuntary reflex, occurring without conscious thought.
Salivation as Part of the Emesis Reflex
Increased salivation is an early component of the body’s broader emesis, or vomiting, reflex. It often precedes sensations like nausea or retching. The entire reflex is a sequence of events designed to expel harmful substances from the stomach. Before the actual expulsion, the body undergoes several preparatory changes.
The process begins with the relaxation of stomach muscles and reverse peristaltic contractions that move contents upwards into the stomach and esophagus. Alongside these gastrointestinal changes, the autonomic nervous system triggers various responses, including increased salivation, sweating, and changes in heart rate. The heightened salivary flow is an integrated part of this protective sequence, providing a physical and chemical barrier against stomach acid even before the contents are expelled.