Vomiting, also known as throwing up or emesis, is the involuntary, forceful expulsion of the contents of one’s stomach through the mouth and sometimes the nose. Vomiting is a symptom of various conditions and an adverse reaction to certain medications or toxins. When vomiting occurs, the body goes through several physiological processes and nerve signals to coordinate the expulsion.
What triggers vomiting?
Vomiting can be triggered by various factors, including:
- Infections – Viral infections like the stomach flu, food poisoning, motion sickness
- Pregnancy – Morning sickness in early pregnancy
- Medications – Chemotherapy drugs, antibiotics, opioids
- Brain conditions – Concussions, brain tumors, migraines
- Digestive problems – Gallbladder disease, blockages, ulcers
- Emotional stress or anxiety
- Unpleasant sights, smells or thoughts
- Overeating, acid reflux, alcohol intoxication
The vomiting center in the brain receives input from various sources like the inner ear, nerves in the stomach and intestine, regions of the brain that control smell and memories, etc. Any discordance in these inputs can trigger nausea and vomiting.
What happens in the brain before vomiting?
The vomiting or emetic center is located in the medulla oblongata of the brainstem. It receives sensory input about the state of the gastrointestinal system and any irritants through:
- The vagus nerve which innervates the stomach and intestine
- The vestibular system of the inner ear which senses motion and equilibrium
- Regions of the brain that control smell and memories
When the emetic center receives stimuli that are different from normal, it sends signals to initiate vomiting. Key steps include:
- Activation of serotonin receptors – These increase gut motility.
- Triggering the nearby chemoreceptor trigger zone – This zone has receptors that sense toxins and drugs in the blood.
- Sending signals through vagus and spinal nerves – To coordinate abdominal muscle contractions and relaxation of the upper gastric sphincter.
- Activation of salivation to protect the teeth from gastric acids.
- Contraction of abdominal muscles along with the diaphragm to build up pressure.
This sequence creates力he familiar nausea and the urge to vomit leading up to the expulsion phase.
What happens in the stomach before vomiting?
As the brain initiates the vomiting reflex, the following changes occur in the gastrointestinal system:
- Peristalsis reverses direction – Stomach contractions propel contents back up instead of pushing them downward.
- The pyloric sphincter tightens to prevent stomach contents from entering the small intestine.
- The lower esophageal sphincter relaxes to allow passage of vomit upwards.
- Saliva production increases to protect tooth enamel from stomach acids.
- Reverse peristalsis starts from the middle and upper parts of the small intestine to move contents back into the stomach.
These coordinated motions result in the contents of the stomach and upper intestine being propelled up the esophagus and out of the mouth.
Visible signs and symptoms before vomiting
In the minutes preceding an episode of vomiting, some common signs and symptoms include:
- Nausea – An uneasy sensation of discomfort and queasiness in the stomach marked by an urge to vomit.
- Increased salivation – More saliva production to protect teeth from stomach acids.
- Sweating and lightheadedness – Due to stimulation of the sympathetic nervous system.
- Skin pallor – Vasoconstriction reduces blood flow causing pale skin.
- Abdominal muscle contractions – To increase abdominal pressure.
- Gagging motions – Involuntary retching as vomit approaches the throat.
- Watering of the eyes and nose – Tearing and runny nose can occur before or during vomiting.
Being aware of these signs and symptoms can provide warning before the involuntary vomiting occurs.
How long does the vomiting reflex take?
The vomiting reflex has four phases from start to finish:
- The prodromal phase – Lasting from a few minutes to hours. Salivation increases and nausea builds.
- The retching phase – Involves forceful contractions of abdominal muscles along with the diaphragm and descent of the esophagus into the thorax.
- The expulsive phase – The actual ejection of gastric contents through forceful contractions of abdominal muscles. It lasts about 3-6 seconds.
- The recovery phase – 10-20 minutes of relaxation as the body recovers, ending with feeling fatigued and hungry.
The entire sequence from nausea to completing all phases takes anywhere between a few minutes to several hours depending on the cause.
Can vomiting be prevented once the urge starts?
Once the vomiting reflex has been triggered and reached the later prodromal or retching phase, it is difficult to stop the process. Some techniques that may pause or delay vomiting include:
- Deep breathing exercises to relax the body.
- Distraction by conversing or watching something.
- Applying a cool compress to the forehead or back of the neck.
- Drinking chilled carbonated beverages.
- Interrupting the gag reflex by swallowing repeatedly.
- Using antiemetic medications if available.
However, these techniques may only delay and not completely prevent vomiting once the urge becomes very strong. Stopping the reflex at that point requires tremendous willpower.
When should you see a doctor?
Occasional vomiting from dietary indiscretion or stomach flu usually requires no medical treatment. However, recurrent episodes of vomiting with moderate to severe intensity, especially when combined with warning signs, need medical evaluation.
See a doctor promptly if vomiting is:
- Projectile and forceful
- Contains blood or has a coffee-ground appearance
- Leads to dehydration
- Caused by head injury
- Accompanied by high fever, stiff neck, rash, etc.
- Persistent for over 48 hours in adults or 24 hours in children
- Making it difficult to keep down medicines or fluids
Such scenarios can indicate potentially serious illnesses requiring specific treatment. The doctor may order lab tests, imaging scans or endoscopy procedures to determine the cause and guide treatment.
Conclusion
Vomiting is designed as a protective mechanism to expel harmful ingested substances or intestinal irritants. It is controlled by the vomiting center in the brainstem which coordinates inputs from various sources.
Discomfort builds during the prodromal phase as the stomach is prepared through reverse peristalsis. Retching motions, nauseating sensation and visible signs precede the expulsive phase.
Once vomiting becomes imminent, it is difficult to interrupt the complex reflex. Treatment is aimed at the underlying cause for recurrent or severe episodes. Being aware of one’s own symptoms can provide advance warning to reach a toilet or grab an anti-emetic medication.