What Is Vomiting And Why Do We Vomit?

The Reasons Why Humans And Animals Throw Up

May 23, 2009 Roberta Goli

Vomiting is an extremely unpleasant function of the human body, but like many functions, it is a protective reflex.

So what exactly is vomiting (emesis) and why do people need this bodily function?

Vomiting is when a person forcibly expels the gastric and duodenal contents from their mouth. Vomiting is a protective reflex. The purpose of vomiting is to remove toxic materials from the gastro-intestinal tract before they are absorbed.

The Vomiting Reflex

The medulla is responsible for coordinating the vomiting reflex. The medulla is a section contained within the brain stem, which controls unconscious or involuntary functions, such as breathing, swallowing, cardiovascular functions and vomiting.

Stimulation of sensory receptors starts the vomiting reflex and a variety of triggers can cause vomiting. Some causes include:

• Drugs
• Chemicals in the Blood
• Pain
• Stress
• Motion sickness
• Tickling the back of the pharynx
• Gastroenteritis
• Food poisoning
• Excessive consumption of alcohol
• Eating disorders (eg: bulimia)
• Serious/various illnesses

The vomiting reflex usually causes a feeling of nausea. The vomiting center in the medulla sends signals through the body, which starts a wave of peristalsis (progressive wave of contraction and relaxation) in the small intestine.

Contractions of the stomach, then relaxation of the stomach increase pressure and forces gastric and intestinal contents out through the esophagus and mouth.

What Happens When We Vomit?

Usually, but not always, vomiting accompanies nausea. Retching or ‘dry heaving’, a spasmodic respiratory action, follows nausea. Immediately before the vomiting occurs, a series of events usually happens. A deep breath is taken and the epiglottis and soft palate close off the trachea and nasopharynx, the diaphragm contracts causing negative pressure, the stomach muscles contract, and the esophagus is open. Next the gastric and intestinal contents are propelled out.

What Is Vomit?

Vomitus (vomit) contains gastric secretions and food that has been eaten recently, and blood and bile in severe cases. People often wonder why there appears to be carrots in their vomit, even when they haven’t eaten carrots for a long time. Generally speaking, it is not carrot pieces that are found in vomit, but rather small pieces of the stomach lining that have been brought up.

Is Vomiting Bad?

When a person vomits, they will notice that it becomes difficult to breathe. Respiration is inhibited as a protective mechanism. The epiglottis and soft palate close off the trachea and nasopharynx so that you wont inhale any gastric or intestinal contents.

Vomiting is bad if stomach acids or food particles get into the airways as they can damage the respiratory system. This could potentially cause aspiration pneumonia (aspirated = inhaled, pneumonia = lung infection).

Excess or prolonged vomiting can cause metabolic alkalosis (increase in the alkalinity of body fluids) due to loss of gastric contents. Other dangers of prolonged or excessive vomiting include dehydration, erosion of teeth enamel and erosions (or tears) in the esophagus.

Resource and further reading:

Silverthorn, D.U, 2007, ‘The Digestive System, in Human Physiology, ed. Benjamin Cummings, San Francisco, chap. 21.

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