We often expect to see partially digested and even undigested food along with stomach fluids when we vomit. This is usually the case for up to a few hours after eating. However, when the stomach and upper part of the small intestine is “empty” of food, vomiting will only lead to the expulsion of the digestive fluids which can be clear in color similar to water has a thicker consistency like mucus or may be a yellow to greenish color.
Vomiting is a result of strong muscle contractions in the first half of small intestine, stomach and even esophagus pushing out the contents of the upper gut. This is in reverse to the direction that food and fluid should be traveling in the gut. It is therefore known as antiperistaltic contractions. To counteract gravity and the sphincters that usually restrict backward flow, vomiting often has to be a strong and violent process.
The vomit centers in the brain initiate the process and are stimulated by a range of factors. Gastrointestinal irritation are by far the most common stimuli. In fact the purpose of vomiting is to expel any noxious substances or irritants inn the upper gut before it can be digested and absorbed into the body. However, there are a range of other factors that can directly or indirectly trigger vomiting.
What is vomit?
Usually when we refer to vomit we actually mean the contents that are expelled. The correct term for this is vomitus. Vomit or vomiting is the act of expelling vomitus. As mentioned, vomitus is composed of:
- Food that is partially digested or undigested as well as beverages that were recently consumed.
- Saliva from the mouth.
- Acid secreted by the stomach wall and bile from the duodenum.
- Digestive enzymes from the stomach and pancreas.
- Mucus from the mouth, esophagus, stomach and small intestine.
- Water from the gastrointestinal tract.
Gastric emptying ensures that food and fluid that was consumed is gradually released into the small intestine as a semi-solid fluid known as gastric chyme. This rapidly moves through the small intestine and if it is low down it will not always be expelled with vomitus.
Therefore clear, watery and mucus vomit usually occurs several hours after the least food that was eaten has passed the esophagus, stomach and upper sections of the small intestine. Essentially the stomach is “empty” as most of us would say. Sometimes clear fluid vomit is what is left after the partially digested and undigested food has already been vomited as is the case with bouts of vomiting and recurrent vomiting.
Causes of Clear Vomitus
The causes of vomiting clear, watery and mucus vomitus is not significantly different from causes of vomiting up food mixed with digestive juices. Some of the causes of food-related vomiting and recurrent vomiting have been discussed below but clear watery vomitus can occur with just about any cause of vomiting.
Gastroenteritis and Food Poisoning
Microbes and the toxins it produces are common causes of acute vomiting and diarrhea that is commonly associated with it may not arise. These microbes and toxins irritate the lining of the gut and triggers vomiting. Viruses, bacteria and parasites are often acquired through contaminated food or water, but sometimes outbreaks of stomach flu occur where the virus is transmitted from one person to another.
When the body does not have the ability to digest or absorb certain foods, then these otherwise harmless edible items can irritate the gut. Lactose intolerance is a well known type of food intolerance. The body cannot digest the milk sugar lactose and vomiting may be one of the symptoms that arise. Gluten intolerance is another common food intolerance caused by the body’s intolerance to gluten, a protein found in certain grains like wheat.
Motion sickness is another common cause that arises with movement. It arises due to the contradictory signals that are normally used to detect motion. Some people are very sensitive and even a short car drive on a smooth road can trigger nausea and vomiting. Others have a greater tolerance and may only become “sick” when on a boat in rocky seas. Long hours of video game playing can sometimes mimic motion sickness, especially fast moving games.
An excess intake of alcohol can lead to vomiting. It is a common symptom that most people experience, particularly binge drinkers. However, some people may vomit even after a single drink. Underlying gastrointestinal problems like peptic ulcers and gastritis are more likely to lead to quicker vomiting with alcohol intake. The body attempts to rid the gut of the alcohol and sometimes the vomiting is excessive even after any remaining alcohol in the gut has been expelled.
Vomiting may occur with migraines even though there is no gastrointestinal irritation. A complex interplay of pain and changes in the brain associated with the onset of migraines can trigger vomiting. Treating the migraine will often cause the accompanying nausea and vomiting to subside.
Although vomiting in certain eating disorders is intentional, like purging in bulimia nervosa, the changes in the gut with the altered eating habits can make it sensitive to food intake. Sometimes it is entirely psychological when a person with an eating disorder is forced to eat and vomiting may occur spontaneously.
Nausea is a common side effect with many pharmaceutical drugs. Sometimes the nausea can be very intense and lead to vomiting. While some drugs may irritate the upper gut, others may stimulate an area in the brain known as the chemoreceptor trigger zone (CTZ) which in turn stimulates the vomit centers in the brain.
Blockage anywhere in the gut can lead to vomiting as food that is eaten distends the upper gut when it becomes backed up. The stagnant food can also irritate the gut. Intestinal obstruction is not uncommon and should be considered especially in babies and children who repeatedly vomit after feeding.
Cyclic Vomiting Syndrome
Cyclic vomiting syndrome is a condition that is mainly seen in children. The exact cause is unknown. It occurs in episodes of recurrent vomiting that lasts for a period of time and the resolves spontaneously. These episodes may then recur weeks or even months later.