Nausea is the feeling of wanting to vomit or feeling uneasy in the stomach, while vomiting is the act of forcefully expelling the contents of the stomach through the mouth.
Nausea and vomiting can be caused by a wide variety of conditions, including:
- Gastrointestinal issues such as food poisoning, stomach viruses, or stomach ulcers
- Migraine headaches
- Pregnancy
- Motion sickness
- Medications and drug use
- Chemotherapy for cancer treatment
- Certain medical procedures, such as surgery
- Certain medical conditions, such as diabetes, kidney failure, or brain tumors
Pathophysiology
Vomiting, also known as emesis, is a complex physiological process involving coordinated interactions between the central nervous system, peripheral nervous system, gastrointestinal tract, and other body systems. The pathophysiology of vomiting can be described as follows:
Nausea and Vomiting Centre (NVC) Activation
- The NVC, located in the medulla oblongata of the brainstem, plays a central role in initiating and coordinating the vomiting response.
- Various stimuli, such as toxins, medications, motion, pain and psychological factors, can activate the NVC.
- Activation of the NVC triggers a series of events that lead to the sensation of nausea and the act of vomiting.
Visceral Stimulation
- Vomiting can be triggered by stimulation of the gastrointestinal (GI) tract, as well as other visceral organs such as the liver, kidneys and uterus.
- Irritation, inflammation, distention or obstruction of the GI tract can activate sensory nerve fibres, known as afferents, which transmit signals to the NVC.
- Visceral stimulation activates receptors, including serotonin (5-HT3) receptors, neurokinin-1 (NK1) receptors and dopamine (D2) receptors, among others, which contribute to the emetic response.
Autonomic Nervous System Involvement
- The autonomic nervous system plays a crucial role in the pathophysiology of vomiting.
- Activation of the sympathetic nervous system leads to increased heart rate, blood pressure and sweating, which are commonly observed during episodes of vomiting.
- Activation of the parasympathetic nervous system can cause excessive salivation, increased gastric secretions, and relaxation of the lower oesophageal sphincter.
Coordinated Muscular Contractions
- Vomiting involves the sequential contraction and relaxation of various muscle groups.
- The diaphragm, abdominal muscles and muscles of the oesophagus and stomach work together to forcefully expel the stomach contents through the mouth.
- The coordinated contractions of these muscles are under the control of the brainstem and mediated by the activation of specific neuronal pathways.
Protective Reflexes
- Vomiting is considered a protective reflex that helps the body expel potentially harmful substances from the GI tract.
- The act of vomiting can help eliminate toxins, irritants, pathogens, or other harmful agents that may have been ingested.
- In addition, the forceful contractions and relaxation of the abdominal muscles during vomiting can help clear the airway and prevent aspiration of gastric contents.
Central and Peripheral Sensitisation
- Prolonged or repeated episodes of vomiting can lead to sensitisation of the emetic response.
- Sensitisation can occur both centrally, at the level of the NVC and peripherally, within the GI tract.
- Central sensitisation involves increased excitability of neurons in the NVC, leading to a heightened response to emetic stimuli.
- Peripheral sensitisation involves increased sensitivity of sensory nerve fibres in the GI tract, making them more responsive to emetic triggers.
SYMPTOMS
Symptoms of nausea and vomiting can vary depending on the underlying cause. Some common symptoms include:
- A feeling of dizziness or lightheadedness
- Sweating
- Pallor (paleness)
- Salivating
- Abdominal pain or discomfort
- Loss of appetite
Treatment of nausea and vomiting depends on the underlying cause. In some cases, such as with motion sickness or a mild stomach virus, over-the-counter medications may be used to relieve symptoms. In other cases, such as with chemotherapy or surgery, medications will be used to prevent nausea and vomiting from occurring.
It is important to note that severe or prolonged nausea and vomiting may lead to dehydration and malnutrition if left untreated.