S1: Nausea, Vomiting and Pain

Question 1

What is nausea?

Answer 1

Nausea is a sensation

• it is personal and self reported.
• associated with physiological changes
• unpleasant
• triggers aversion which is a feeling of repugnance towards something with a desire to avoid

Question 2

What is vomiting?

Answer 2

Vomiting is a physical act

• it expels content of the upper GI tract via the mouth
• it is forceful
• it is a complex, coordinated reflective event
• associated with a sensation of relief

Question 3

What is the medical name for vomiting?

Answer 3

Emesis

Question 4

Is nausea produced by the same stimuli as vomiting?

Answer 4

Yes

Question 5

Nausea is recognised as a prodrome. What does this mean?

Answer 5

Prodrome is a warning symptom

Nausea is therefore a warning symptom of vomiting

Question 6

List some causes of nausea and vomiting

Answer 6

Poisoning 
Gastroenteritis
Excessive alcohol
Pregnancy
Excessive eating
Travel sickness
Metabolic disturbances
Drugs
GI disease
Emotional upset

Question 7

What is the benefit to vomiting?

Answer 7

It acts as protection against ingested toxins

Question 8

What is the first defence against ingested toxins?

Answer 8

Taste and smell

Question 9

How does our body protect us from toxins - especially in children?

Answer 9

Children are wary of new flavours and we have a built in dislike of bitter flavours.
Children also learn from elders and aversion hardwired this knowledge

Question 10

What happens when our body creates incorrect associations to stimulus?

Answer 10

People can feel nausea and vomit at normal stimuli e.g. seafood

Question 11

Explain how our gastric and upper GI afferent fibres help prevent ingested toxins

Answer 11

They expel potentially harmful agents before they have much chance to be absorbed in the body

Afferents are associated with chemoreceptive cells embedded in the gut wall

They respond to contaminants in blood

Question 12

Where is the chemoreceptors trigger zone?

Answer 12

The area postrema in the brain stem (medulla)

Question 13

Explain the chemoreceptor trigger zone

Answer 13

The chemoreceptor trigger zone is found in the brain stem (medulla)

The blood brain barrier is leaky and chemoreceptors can detect toxins in the blood

Question 14

What is the vestibular system?

Answer 14

It is the organ of balance and potential trigger of emesis.
It may be activated by toxins in the blood or disequilibrium resulting in poisoning

Poisoning is thought to produce aberrant activity in vestibular neural pathways

Question 15

What is the disadvantage with the vestibular system?

Answer 15

It triggers nausea and vomiting in response to unnatural motion e.g. on boat as it assumes that poison may have been ingested

Question 16

Where is the nucleus tractus solitaries found and what’s its role?

Answer 16

It is located in the medulla of the brain stem and integrates cardiac, respiratory and gastrointestinal functions.

The NTS is the coordinator/regulator

Question 17

Where do the abdominal afferents travel to?

Answer 17

The nucleus tractus solitaries by vagus nerve

Question 18

Where are visceral afferent receptors found?

Answer 18

They are found in the fundus and duodenum

Question 19

Examples of visceral afferents that can trigger nausea and vomiting

Answer 19

Toxins
Irritants
Distension

Question 20

Briefly explain the pathway the visceral afferents take

Answer 20

The afferents take information via the vagus nerve (parasympathetic system)

Question 21

Where do fibres from the vestibular system travel?

Answer 21

They travel to the NTS (nucleus tractus solitarius) after detecting toxins or disequilibrium

Question 22

What do the fibres from the area postrema do?

Answer 22

They detect toxins in the blood

Question 23

What reduces area postrema and abdominal afferent signalling to NTS?

Answer 23

5-HT3 antagonist

It reduces nausea and vomiting

Question 24

Name 3 mechanisms of nausea

Answer 24

1. Reduced gut motility (mixing and peristalsis) prevents toxins from being carried further through the system
2. Proximal stomach relaxes to receive additional contents
3. Giant retrograde contraction occurs, that sweeps up from the midsmall intestine and returns upper intestinal contents to stomach

Question 25

Name the structure that the NTS signals to for nausea

Answer 25

Frontal cortex

Question 26

What happens when NTS signals the hypothalamus?

Answer 26

The hypothalamus will release ADH which helps conserve water so less is lost during vomiting

Question 27

What happens when NTS signals the the frontal cortex?

Answer 27

Nausea

Question 28

What happens when NTS signals the autonomic efferents?

Answer 28

1. Changes in gut motility | 2. Salivation, vasoconstriction in GIT and skin, sweating

Question 29

Name the 2 structures that the NTS signals to for vomiting

Answer 29

Autonomic efferents Hypothalamus

Question 30

Mechanism of vomiting

Answer 30

1. Vomiting is going to occur, typically there will be RETCHING (dry heaves). These are coordinated contractions of the abdominal muscles by phrenic nerve. Waves of Hugh pressure in the abdomen compress the stomach but the anti reflux barriers (oesophageal sphincters and crural diaphragm) are intact, so there is no expulsion 2. Then is emesis. The oesophageal sphincters and crural diaphragm relax and further waves of contractions of the stomach expel stomach contents

Question 31

How is the mechanism of vomiting different to nausea

Answer 31

In vomiting, NTS will use somatic and autonomic efferents to cause changes in gut motility and expulsion as well as salivation , vasoconstriction and sweating

Question 32

What nerve innervates the abdominal muscle?

Answer 32

Somatic nerve

Question 33

What nerve innervates the diaphragm?

Answer 33

Phrenic nerve

Question 34

Name the 2 anti-reflux barriers

Answer 34

Oesophageal sphincters and crural diaphragm

Question 35

What are sensory receptors for pain called?

Answer 35

Nociceptors

Question 36

Name the 2 nociceptors in the GI

Answer 36

Arc stretch receptors | Chemoreceptors

Question 37

Name some noxious stimuli

Answer 37

``` Distension Inflammation Ischaemia Traumatic injury Muscle spasm ```

Question 38

Are most GI nociceptors afferent axons sympathetic or parasympathetic?

Answer 38

They mostly run in the sympathetic nerves (the greater and lesser splanchnic nerves)

Question 39

Explain distension of the stomach

Answer 39

Wide dynamic range cell fires infrequent AP when gut is not very distended. The AP frequency increases as distension increases. Nociceptors specific cells only start to fire when the amount of distension becomes grossly abnormal so signal to the brain. The brain produces signals felt as pain.

Question 40

Nociceptors respond to inflammatory mediators and produce some of their own. What happens to the GI if cell receptors become hypersensitive due to inflammation?

Answer 40

Normal levels of inflammation and normal gut distension will feel painful The wide dynamic range cell will fire more frequently at low levels of distension as will the nociceptors specific cell

Question 41

Characteristics of visceral pain

Answer 41

1. Diffuse and poorly localised 2. Pain is generally referred to regions of the body wall 3. Each organ has a characteristic pattern of referral

Question 42

Explain how visceral pain is diffuse and poorly localised

Answer 42

There are relatively small number of afferents and there is diffuse innervation of organs. The pathways are divergent

Question 43

Explain how visceral pain is often referred to regions of the body wall

Answer 43

This is due to viscera-somatic convergence. This means that visceral afferents travel with somatic nerves which innervate a similar body wall

Question 44

Explain how each organ has a characteristic pattern of referral for visceral pain

Answer 44

Pain is referred to the dermatomes marching the embryonic origin of the organ. The site and nature may change as well as other tissues that are affected