Nausea is the sensation of discomfort in the upper stomach that gives a person the feeling or the urge to vomit. Vomiting is the action of expelling the contents of the stomach through the mouth. Typically one feels queasy prior to vomiting; however, it is not uncommon to vomit without experiencing nausea. By itself, nausea is not debilitating unless there is a prolonged feeling of nausea.
Nausea is a nonspecific symptom and can have many causes. These causes include but are not limited to (1) food poisoning, (2) pregnancy, (3) side effects of medication, (4) anxiety, (5) stress, (6) depression, and (7) motion sickness. The two most common causes are gastrointestinal infections and food poisoning.
Food poisoning occurs when bacteria in the food one eats produces toxins, which can cause a very abrupt and sudden onset of nausea and vomiting. Nausea, or morning sickness, is commonly caused by pregnancy usually in the early stages (the first three months or trimester). Nausea from pregnancy and many other causes is usually mild and does not require treatment.
However, there are some cases of nausea that do require immediate attention, but these cases come with more often severe symptoms. These cases include but are not limited to (1) appendicitis, where the appendix becomes inflamed or infected: (2) a brain tumor; (3) a heart attack; (4) meningitis, where the meninges (protective covering that surrounds the central nervous system) becomes infectious; (5) hepatitis, an illness of the liver; and (6) carbon monoxide poisoning.
The diagnosis of nausea usually begins with the patient’s history. The patient is asked questions about when the nausea started, how long he or she has felt nauseated, and if it is constant. A typical diagnosis of acute onset of nausea is normally related to drugs, toxins, or infections. If nausea has been long-lasting, then it is normally related to a more chronic illness. If nausea occurs about an hour after eating, then there might be an obstruction that is proximal to the small intestine. If a patient vomits and then feels relief in the abdomen, then it is likely an obstruction is a cause and not a chronic issue like pancreatitis or gallstones (choleocystitis), both of which are not relieved by vomiting.
The central nervous system plays a vital role in nausea suppression. Areas including the limbic system and cerebral cortex are activated by an increase in intracranial pressure, meningeal irritation, or emotional triggers. Housed in the fourth ventricle of the brain are chemoreceptor trigger zones (CTZs). CTZs are outside of the blood-brain barrier and are always exposed to substances and/or toxins circulating in the blood and cerebral spinal fluid. CTZ activation is controlled by dopamine, serotonin, and neurokinin receptors. The vestibular system is located in the inner ear and can be activated by movements that cause motion sickness and dizziness. This system is triggered via histamine and acetylcholine receptors.
These three pathways have receptors that respond to a stimulus and travel to the brainstem. This in turn activates structures including but not limited to the nucleus of the solitary tract, the dorsal motor nucleus, and the central pain generator. Continuing downstream, the body’s motor response halts the muscles of the gastrointestinal tract and causes reverse propulsion of gastric contents to the mouth while abdominal contractions increase. There are autonomic effects involved that increase a sense of feeling faint, in which nausea and vomiting generally occur shortly after.
The treatment for nausea can vary depending on the underlying cause. Treatments usually include rehydration if one is dehydrated, medication to suppress the queasiness of the stomach and bowels, acupuncture, and other alternative medications. It is recommended to seek medical care if one cannot keep any liquids down, has symptoms for more than two days, is weak, has a fever, has severe stomach pain, vomits more than two times in one day, or does not urinate for more than eight hours.
Avoiding nausea may be hard, but there are some ways to do so. The most common is eating smaller meals throughout the day, eating them slowly, and resting after eating. Avoiding certain foods that irritate one’s stomach is also a good way to avoid nausea. Drinks like ginger ale are common to try when experiencing nausea as well as eating high-protein foods such as cheese or meat before standing up.
See also: Autonomic Nervous System; Chemoreception; Dizziness; Emesis; Vestibular System
Blake, Katie. (2015). Nausea and vomiting. Healthline Medical Review Team. Retrieved from http://www.healthline.com/health/nausea-and-vomiting#Prevention6
Singh, Prashant, Sonia S. Yoon, & Braden Kuo. (2016). Nausea: A review of pathophysiology and therapeutics. Therapeutic Advances in Gastroenterology, 9(1), 98—112. http://dx.doi.org/10.1177/1756283X15618131