Nausea and vomiting

Question 1

What is nausea often accompanied by?

Answer 1

• cold sweat
• pallor
• salivation
• disinterest in surroundings
• loss of gastric tone
• duodenal contractions
• reflux of intestinal contents into stomach

Question 2

What are the common causes of nausea and vomiting?

Answer 2

1. gastroparesis
2. general anaesthesia
3. intestinal obstruction
4. migraine
5. rotavirus
6. viral gastroenteritis
7. vestibular neuritis
8. motion sickness
9. medication
10. chemotherapy

Question 3

Where is the chemoreceptor trigger zone located?

Answer 3

Within the area postrema in medulla oblongata and lies outside the BBB

Question 4

What receptors are found at the ‘vomiting centre’/chemoreceptor trigger zone?

Answer 4

• dopamine D2 receptors
• serotonin 5-HT3 receptors
• opioid receptors
• acetylcholine receptors
• receptors for substance P

Question 5

What 3 types of output are initiated by the chemoreceptor trigger zone?

Answer 5

1. Motor
2. Parasympathetic
3. Sympathetic

Question 6

Explain how motion sickness occurs?

Answer 6

• issue arises in the labyrinth (vestibule - responsible for balance and space)
• transmitted as electrical signals via the vestibulocochlear nerve
• stimulating the vestibular nuclei in the pons via H1 and M1 receptors
• stimulates the area postrema and the rest of the vomiting centre
• feed into brainstem motor nuclei resulting in vomiting

Question 7

What CN is activated when the pharynx is irritated leading to the gag reflex?

Answer 7

Vagus (CN X)

Question 8

How does vomiting, as a result of irritation to the GIT, occur?

Answer 8

• enterochromaffin cells of the gastric mucosa are irritated by cytotoxins, poisons, damage, ischaemia, obstruction, pain, pregnancy, post-op
• enterochromaffin cells release serotonin in response to irritation
• Serotonin stimulates the vagus nerve via 5-HT3 receptors
• Vagus nerve stimulates the vomiting centre via NK1 receptors

Question 9

What receptors do higher brain centres act on in order to stimulate vomiting?

Answer 9

Act on muscarinic receptors in the vomiting centre

Question 10

what occurs when the CTZ initiates motor, PNS and SNS outputs?

Answer 10

1. Increased salivation to protect tooth enamel from stomach acids. (PNS output)
2. The body takes a deep breath to avoid aspirating vomit.
3. Retroperistalsis starts from the middle of the small intestine and sweeps up digestive tract contents into the stomach, through the relaxed pyloric sphincter.
4. Intrathoracic pressure lowers , coupled with an increase in abdominal pressure as the abdominal muscles contract, propels stomach contents into the oesophagus as the lower oesophageal sphincter relaxes. The stomach itself does not contract in the process of vomiting except for at the angular notch, nor is there any retroperistalsis in the oesophagus.
5. Vomiting is ordinarily preceded by retching.
6. Vomiting also initiates an SNS response causing both sweating and increased heart rate.