Nausea, Vomiting & Pain

Question 1

What is nausea?

Answer 1

Nausea is a sensation of feeling sick

Question 2

What does nausea trigger?

Answer 2

Triggers aversion

Question 3

What does vomiting expel?

Answer 3

expels contents of upper GI tract via mouth

Question 4

What is both nausea and vomiting produced by?

Answer 4

Nausea is produced by the same stimuli as vomiting

Question 5

What is nausea in relation to vomiting?

Answer 5

Nausea is generally a prodrome (ie premonitory symptom) of
vomiting

Question 6

What are the different protections against ingested toxins?

Answer 6

1. Taste and smell
2. Gastric and upper GI afferents
3. Chemoreceptor trigger zones
4. Vestibular system
5. Experience

Question 7

What are the chemoreceptor trigger zone to protect against ingested toxins?

Answer 7

1. the area postrema in the brainstem
2. chemoreceptors that can detect toxins in the
   blood

Question 8

What is the vestibular system?

Answer 8

the organ of balance, but also a potent
trigger for emesis

Question 9

What does poisoning produce in the vestibular neural pathways?

Answer 9

poisoning is thought to produce aberrant
activity in vestibular neural pathways

Question 10

What coordinates nausea and vomiting?

Answer 10

Nucleus tractus solitarius(NTS)

Question 11

Where is the NTS found?

Answer 11

Found in the medulla of the brainstem

Question 12

How many different types of warning does the NTS receive and what are they?

Answer 12

1. Visceral afferents for nausea and vomiting(parasympathetic)
2. Area postrema(chemoreceptive trigger zone)
3. Vestibular system
4. Higher brain centres

Question 13

How does the visceral afferent for nausea and vomiting warn the NTS?

Answer 13

-Afferent signals like toxins and irritants stimulate vagus afferent nerves in stomach and duodenum which send signals to the NTS

Question 14

How does the area postrema warn the NTS?

Answer 14

-Detects toxins in blood as there is no blood-brain barrier

Question 15

How does the vestibular system warn the NTS?

Answer 15

Toxins from the blood, un-natural movement triggers cranial nerve 8 which alerts the NTS

Question 16

How does higher brain centres alert NTS?

Answer 16

-Things that your social group find disgusting
-Other people in your group being sick
-Things that made you sick in the past

Question 17

What does the outputs from the NTS do the hypothalamus do?

Answer 17

↑ antidiuretic hormone (ADH; vasopressin)

Question 18

What does the outputs from the NTS do to the higher centres?

Answer 18

nausea,
future avoidance

Question 19

What does the outputs from the NTS do to autonomic efferents?

Answer 19

-changes in gut motility
-↑ salivation, vasoconstriction in GIT

Question 20

How does the NTS trigger nausea?

Answer 20

1. Reduced mixing and peristalsis
   * prevents toxins from being carried prevents toxins from being carried
   further through the systemfurther through the system
2. Proximal stomach relaxes2. Proximal stomach relaxes
   * prepares stomach to receive
   additional contents
3. Giant retrograde contraction3. Giant retrograde contraction
   * sweeps up from mid-small intestine
   * returns upper intestinal contents to
   stomach

Question 21

How does the NTS trigger vomitting?

Answer 21

4. Retching (dry heaves)Retching (dry heaves)
   * co-ordinated contractions of
   abdominal muscles and diaphragm
   * waves of high pressure in abdomen
   * compresses stomach but anti-reflux
   barriers intact so no expulsion
5. Vomiting (emesis)Vomiting (emesis)
   * oesophageal sphincters and crural
   diaphragm relax
   * further waves of contraction expel
   stomach contents

Question 22

How do the visceral afferents work for pain sensation?

Answer 22

1. Damaging events cause afferent signals
2. Signals from the stomach and lower esophagus are transmitted via the sympathetic greater splanchnic nerve at T1-9
3. Signals from the small intestine, descending colon and sigmoid colon via the lesser splanchnic nerves at T10-T12

Question 23

What are nociceptors?

Answer 23

Receptors in the pain pathways respond to “noxious” stimuli, and
are therefore called “nociceptors”

Question 24

What are examples of noxious stimuli?

Answer 24

• distension
• inflammation
• muscle spasm

Question 25

What is the response of nociceptors to stretching of the gut wall?

Answer 25

As gut distention increases, pain increases

Question 26

What do nociceptors respond to?

Answer 26

Nociceptors respond to inflammatory mediators, as well as
stretching of the gut wall:
-injury
-toxins
-infection

Question 27

What do nociceptors release and what feedback loop does this create?

Answer 27

• Nociceptors also release chemicals that increase
  inflammatory responses
• This creates a positive feedback loop, that may become self-sustaining

Question 28

What is thought to occur in GI disease in regards to visceral pain pathways?

Answer 28

Chronic sensitisation of visceral pain pathways is thought to
occur in GI disease

Question 29

How are somatic pain pathways organised?

Answer 29

Somatic pain
pathways are precisely
organised

Question 30

How are visceral pain pathways organised and what can this cause?

Answer 30

Visceral pain pathways piggy-back onto somatic
pathways. Hence why this can cause referred pain.

Question 31

What is visceral pain referred to and what is this due to?

Answer 31

Generally “referred” to regions of the body wall
- due to viscero-somatic convergence

Question 32

Why does visceral pain often diffuse and poorly localized?

Answer 32

• relatively small number of afferents
• imprecise wiring

Question 33

What does each organ have a characteristic pattern of in visceral pain and what can this evolve to?

Answer 33

Each organ has a characteristic pattern of referral
- initially to dermatomes matching the embryonic origin of the organ
- but may evolve as neighbouring tissues are affected