Physiology of Vomiting [Simplified Mechanism] with Clinical Correlation [Metabolic Alkalosis]

Physiology of Vomiting [Simplified Mechanism] with Clinical Correlation [Metabolic Alkalosis]

Before we start learning physiology of vomiting, a simple yet complex question arises in mind  “What is the physiological function of vomiting? ”

              our physiological capabilities presumably were developed in an evolutionary window of time that was quite different from the one we now inhabit; a biology designed for racing across the Savannah to spear the next meal is quite different from what is needed to make a trip to the supermarket. Food intake is a risky behavior leading to the exposure of internal organs to possible food-related ailments, including viral and bacterial infection, allergies, and food intolerance .

Smell and taste, the gatekeepers of the alimentary tract, are not always effective in detecting the quality of food, and nausea and vomiting, as additional mechanisms for dealing with an unhealthy meal, play a large role in subsequent levels of defense. Vomiting, along with diarrhea, helps rid the gastrointestinal tract of dangerous ingested toxins.

We also have the unfortunate neurological connection between motion  and vomiting. Motion-induced nausea and vomiting is thought to result from sensory conflict regarding body position in space.

Physiology of Vomiting/Emesis

Vomiting (emesis) is controlled by the vomiting center of the medulla, which can be stimulated by afferents from: 

• Gastric overdistention.
• Oropharyngeal stimuli.
• Chemoreceptor trigger of the area postrema of the medulla. 
•  Vestibular stimulus.

The vomiting reflex includes several sequential actions: 

1. Reverse peristalsis (from the small intestine),
2.  Relaxation of the stomach and pylorus,
3.  Forced inspiration (increases abdominal pressure),
4.  Relaxation of the LES, and 
5. Forceful expulsion.

Fig: Neural pathways leading to the initiation of vomiting in response to various stimuli.

Clinical Sequel Of Vomiting 

• Aspiration

• Mallory Weiss Syndrome

                      Due to sever and repetitive retching and vomiting partial tear of the mucosa and                                sub-mucosa in the stomach & gastroesophageal junction Bleeding

• Electrolyte Imbalance

 Volume depletion 

Hyperaldosteronism 

Increased re-absorption of Sodium 

Increased Excretion of large amounts of Potassium in the urine

Leading to Hypokalemia which further induces metabolic alkalosis

For detailed flow chart on physiology of vomiting ,please visit link provided below.