Symptoms of GI Disease: Nausea & Vomiting

Question 1

What is nausea?

Answer 1

Nausea is a sensation 
personal, self reported
associated with physiological changes
unpleasant
triggers aversion

Question 2

What is vomiting?

Answer 2

Vomiting (emesis) is a physical act:
expels contents of upper GI tract via mouth
forceful (cf regurgitation, reflux)
complex, co-ordinated reflexive events
associated with sensation of relief

Question 3

Describe the relationship between Nausea and vomiting

Answer 3

Nausea is produced by the same stimuli as vomiting
Nausea is generally a prodrome (ie premonitory symptom) of vomiting
BUT nausea may clear up without triggering vomiting
AND vomiting can occur without prior nausea

Question 4

What are the causes of nausea and vomiting (emetic stimulus)?

Answer 4

GI infection (eg norovirus)
Pregnancy 
Travel sickness
Other people being sick 
Metabolic disturbance 
Drugs (e.g. morphine chemotherapy)
Raised intracranial pressure 
GI disease (e.g. gastritis, kidney stones)
Emotional upset

Question 5

Describe when vomiting and nausea is advantageous

Answer 5

Poisoning (eg contaminated food, poisonous plants, chemical agents)
Obstruction
Excessive alcohol
Excessive eating

Question 6

How are we protected against ingested toxins?

Answer 6

Taste and smell can potentially prevent ingestion
we have a built-in dislike of bitter flavours
children are wary of novel flavours; we learn from our elders what is safe

Question 7

Explain how gastric and GI afferents help expel ingested toxins

Answer 7

can potentially expel harmful agents before they have (much) chance to be absorbed
associated with chemoreceptive cells that respond to:
irritants
inflammatory mediators
bacterial (and some other) toxins

Question 8

What effect do non-ingetsed toxins have?

Answer 8

non-ingested toxins will have the same effect as ingested toxins – eg chemotherapy, systemic infection, metabolic disturbance, iv

Question 9

What is the chemoreceptor trigger zone

Answer 9

The chemoreceptor trigger zone is the area postrema in the brainstem responds to circulating poisons
blood-brain barrier has to be “leaky”

Question 10

What is the blood brain barrier?

Answer 10

Within the brain, capillaries have endothelial walls with tight junctions, so substances have to be carried into / out of brain tissue - protection
In area postrema blood brain barrier is leaky so substances from plasma can cross into the tissue to trigger nausea

Question 11

What is the vestibular system?

Answer 11

This is the organ of balance, but also a potent trigger for emesis
Poisoning is thought to produce aberrant activity in vestibular neural pathways
BUT also triggers Nausea & Vomiting in response to un-natural motion

Question 12

How do we prevent ingesting toxins in the future?

Answer 12

If we survive a mistake we avoid repeating it (unpleasantness reinforces learning)
aversion may hard-wire avoidance
But can create incorrect associations

Question 13

What are our anti-poison defences co ordinated by?

Answer 13

Our anti-poison defences are coordinated by the nucleus tractus solitarius (NTS), found in the medulla of the brainstem

Question 14

What are the other functions of the NTS?

Answer 14

It also integrates cardiac, respiratory and gastrointestinal functions

Question 15

What are the 4 different types of ‘warning’ inputs received by the NTS?

Answer 15

1. Visceral Afferents
2. Area Postrema
3. Viestibular system
4. Higher Centres

Question 16

Describe how the visceral afferents cause a response to toxins

Answer 16

axons run through parasympathetic nerves, Vagus → directly into brainstem associated with receptors that respond to toxins, irritants, distension etc.

Question 17

Where is the area postrema located?

Answer 17

Chemoreceptive zone (no blood-brain barrier) in medulla, below cerebellum and very close to foramen magnum

Question 18

What is the foramen magnum?

Answer 18

the hole in the base of the skull through which the spinal cord passes

Question 19

Explain how raised intercranial pressure causes nausea and vomiting

Answer 19

Raised intracranial pressure causes nausea and vomiting, as the increased pressure can only be relieved by pressing brainstem down, through foramen magnum - area postrema compressed

Question 20

Describe the vestibular system

Answer 20

Organ of balance, inner ear
Toxins in blood (disrupting vestibular receptors)
Triggers motion sickness

Question 21

How does the NTS cause Nausea?

Answer 21

NTS signals hypothalamus to release ADH to conserve fluid, increases sympathetic activity and decreased Parasympathetic activity to upper GI tract to stop gastric emptying - paleness & sweating

Question 22

How does the NTS cause vomiting?

Answer 22

NTS coordinates muscles involved to increase pressure on abdomen and release of anti-reflux barriers to prevent reflux of gastric contents up oesophagus

Question 23

Explain the mechanism of the vagus nerve to produce vomiting and nausea

Answer 23

1. Reduced mixing & peristalsis due to decreased Parasympathetic activity
2. Relaxation of the Proximal stomach
3. Giant retrograde contraction

Question 24

Explain how reduced peristalsis due to decreased p/s activity causes nausea and vomiting

Answer 24

Reduced mixing & peristalsis due to decreased Parasympathetic activity
Prevents toxins from being carried further through the system
Stop processing food and stop pushing it down

Question 25

Explain how relaxation of the stomach causes nausea and vomiting

Answer 25

Proximal stomach relaxes
Prepares stomach to receive additional contents
Relaxed muscle = very distensible

Question 26

How does giant retrograde contraction cause vomiting and nausea?

Answer 26

Giant retrograde contraction
(reverse of peristalsis) squeezing mechanism to bring food back up
Sweeps up mid-small intestine
Returns upper intestinal contents to stomach

Question 27

How do the phrenic nerves cause vomiting and nausea?

Answer 27

4. retching (dry heaves)

5. Vomiting (emesis)

Question 28

Explain how retching causes nausea and vomiting

Answer 28

Retching (dry heaves)
coordinated contractions of abdominal muscles and diaphragm
waves of high pressure in abdomen
compresses stomach but anti-reflux barriers intact so no expulsion

Question 29

Explain how the phrenic nerves cause vomiting

Answer 29

Vomiting (emesis)
oesophageal sphincters and crural diaphragm relax
further waves of contraction expel stomach contents

Question 30

How is visceral pain detected?

Answer 30

“Pain” receptors respond to “noxious” stimuli, and are called nociceptors
They respond to:
distension
inflammation
muscle spasm
resulting in pain

Question 31

Describe the innervation resulting in pain

Answer 31

Nociceptor receptors associated with axons running through sympathetic nerves into thoracic segments

Question 32

Describe the normal gut distension

Answer 32

these are the normal levels of distension seen during peristalsis / mixing movements. We are unaware of this occurring

Question 33

Explain pathological distension

Answer 33

← Pathological distention will stretch the gut wall to a potentially damaging degree, producing pain.

Question 34

How is pain produced during pathological gut distension?

Answer 34

Nociceptive fibres are present in the gut wall that respond to the stretching of the gut wall. The more stretched the gut wall = the more action potentials produced by the nociceptive fibres per second
The brain only produces visceral pain sensation in response to high frequency of action potentials firing

Question 35

What induces inflammation in the gut?

Answer 35

Nociceptors respond to inflammatory mediators, as well as stretching of the gut wall:
Injury 
Toxins 
Irritants 
Infection 
Autoimmunity

Question 36

How do inflammatory mediators affect nociceptive fibres?

Answer 36

Inflammatory mediators will depolarise nociceptors, make them fire action potentials, sensitising them to being stretched to produce a higher level of firing

Question 37

When does chronic sensitisation of visceral pain pathways occur?

Answer 37

In GI disease

Question 38

Explain how inflammatory bowel disease is contributed towards by nociceptor fibres

Answer 38

Nociceptors respond to inflammatory mediators but also release pro-inflammatory chemicals when depolarised (e.g substance P)
Causes Positive feedback loop between inflammation and the release of pro-inflammatory chemicals from nociceptors which may contribute to inflammatory bowel disease

Question 39

How is chronic pain caused by nociceptive fibres?

Answer 39

The pain pathways can become potentiated so that normal signals from nociceptors are magnified, and can become self sustaining leading to chronic pain with no obvious cause.

Question 40

What is somatic pain?

Answer 40

precisely localised (somatosensory cortex → T3 somatic nociceptor activated to specific area) e.g. if stabbed with pin in chest: 
Nociceptive fibre fires axon to T3
T3 somatic pathway leads to somatosensory cortex, where pain is specified on map

Question 41

What is visceral pain?

Answer 41

is diffuse & variable, (viscerosomatic convergence, C2 - T4 somatosensory → oesophagul & somatic nociceptive receptors)

Question 42

Describe how visceral pain is felt

Answer 42

location of pain reported following activation of oesophagul nociceptors to T3 which also follows somatic pathway to produce pain in chest wall despite initiating in oesophagus as oesophagus not represented on somatosensory cortex

Question 43

Explain why visceral pain is poorly localised?

Answer 43

Often diffuse and poorly localised
relatively small number of afferents
imprecise wiring

Question 44

Why is visceral pain referred to regions rather than precisely located?

Answer 44

Generally “referred” to regions of the body wall due to viscerosomatic convergence (C2 - T4)

Question 45

Explain how visceral pain is referred to different areas of the body

Answer 45

Each organ has a characteristic pattern of referral
Afferents synapse in segments matching the embryonic origin of each organ
May evolve as other tissues are affected

Pain is felt in the dermatome belonging to the segment of origin of the organ

Question 46

What are dermatomes?

Answer 46

Regions of the body sending somatic afferents to each spinal cord segments
Each visceral organ sends input to spinal cord segment correlating with the somite the organ developed from in the embryonic state