Symptoms of GI disease: nausea, vomiting and pain Flashcards

1
Q

Why is nausea a sensation?

A
  • personal, self-reported
  • associated with physiological changes - we can sometimes tell
  • unpleasant  avoidance/aversion
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2
Q

Describe the premise of vomiting (emesis)?

A
  • expels contents of upper GI tract via the mouth
  • forceful (cf regurgitation, reflux)
  • complex, co-ordinated reflexive events
  • associated with sensation of relief
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3
Q

What is the relationship between vomiting and nausea?

A
  • Nausea is produced by the same stimuli as vomiting
  • Nausea is generally a prodrome (ie premonitory symptom) of vomiting
  • Nausea may clear up without triggering vomiting
  • AND vomiting can occur without prior nausea
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4
Q

What causes nausea and vomiting?

A

On image

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5
Q

What is the advantage of vomiting and nausea?

A
  1. Poisoning
  2. Obstruction
  3. Excessive alcohol
  4. Excessive eating
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6
Q

How are taste and smell involved in protecting us against toxins?

This is the first line of defence

A
  • 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
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7
Q

How are gastric and upper GI afferents involved with protecting us against toxins?

This is the second line of defence

A

Gastric and upper GI afferents - This occurs in the stomach and upper intestine

• 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

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

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8
Q

How does the Chemoreceptor Trigger Zone protect us against toxins?

This occurs when the toxins are absorbed into the blood stream

A

Chemoreceptor Trigger Zone - in the brainstem, they respond to toxins.

  • the area postrema in the brainstem
  • blood-brain barrier is “leaky”
  • chemoreceptors that can detect toxins in the blood
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9
Q

How does the Vestibular system protect us against toxins?

Where are they found and what do they do?

A

Found in the inner ear - involved with motor control

They are sensitive to toxins - signals to the brain

  • 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 N & V in response to vestibular dysfunction

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10
Q

How is the premise of: Prevention of ingestion – learning and aversion involved with protection?

I.e Once we have eaten something bad - we don’t want to do it again

A

• if we survive a mistake we avoid repeating it (unpleasantness reinforces learning)
• aversion may hard-wire avoidance
BUT can create incorrect associations - what happens we have kidney therapy and cancer therapy - the brain can associated meals with experiences

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11
Q

What are our anti-poison defences are coordinated by?

A

Nucleus Tractus Solitarius (NTS)

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12
Q

Where is the Nucleus Tractus Solitarius (NTS) found?

A

Found in the medulla of the brainstem

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13
Q

What does the NTS integrate?

A

It also integrates cardiac, respiratory and gastrointestinal functions

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14
Q

What four different warning inputs activate the NTS?

First input

A
  1. Visceral afferents that run via parasympathetic nerves through the vagus into the brainstem - caused by toxins, irritants, inflammation and distension
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15
Q

What is the area postrema and what does it control?

What is the second input that activates the NTS?

A

Area postrema

Chemoreceptive zone (no blood-brain barrier) in medulla

It detects toxins in the blood, as well as pressure that can affect the brainstem

The area postrema is a medullary structure in the brain that controls vomiting. Its privileged location in the brain also allows the area postrema to play a vital role in the control of autonomic functions by the central nervous system.

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16
Q

What does the Vestibular system do?

The third input to the NTS

A

The organ of balance, inner ear

Detects toxins in the blood and motion sickness

17
Q

What do higher centres do?

The fourth input to the NTS?

A
  • things that have made you sick in the past
  • other people in your group being sick

Somone sick makes you sick

18
Q

Summarise the 4 inputs we have described and the outputs

A

On image

19
Q

Describe the mechanisms of nausea

A

Mediated by the parasympathetic nervous system

  1. Reduced mixing and peristalsis
    • prevents toxins from being carried further through the system
    Getting rid of stuff in the stomach and small intestine
  2. Proximal stomach relaxes
    • prepares stomach to receive additional contents
  3. Giant retrograde contraction
    • sweeps up from mid-small intestine
    • returns upper intestinal contents to stomach
20
Q

Describe the mechanisms of vomiting

What are they mediated by?

A
  1. 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

Mediated by the phrenic nerves

  1. Vomiting (emesis)

oesophageal sphincters and crural diaphragm relax

further waves of contraction expel stomach contents

Mediated by the somatic nerves

21
Q

What receptors mediate viseral pain?

what do they cause?

A

Nociceptor receptors - these run through the sympathetic nerves into the thoracic segments

They produce pain

22
Q

What do pain receptors respond to?

A

Respond to “noxious” stimuli, and are called “nociceptors”

They respond to:

  1. Distension - the receptors fire more with greater distention
  2. Inflammation - Nociceptors respond to inflammatory mediators, as well as stretching of the gut wall:
injury
irritants
toxins
infection
autoimmunity

3 Muscle spasm

23
Q

What does the release of pro-inflammatory chemicals from nociceptors cause?

A

This causes a positive feedback loop, that may contribute to inflammatory bowel disease

Abnormal activity can potentiate synapses, magnifying the nociceptor signals further

And can become self-sustaining, leading to chronic pain with no obvious cause.

Produces more inflammation producing more firing of receptors

24
Q

What causes pain to be felt in the correct regions of the body and not in the correct regions?

A
  1. Somatic nociceptive endings are found within the skin
  2. Activation of these receptors activates the somatosensory cortex (in the cerebral cortex) via the spinal cord
  3. Stimulation of this coordinates the pain to the correct region of the body
  4. Other pain receptors can link to this pathway so pain is felt somewhere else e.g oesophageal nociceptor, occurs in wide area
25
Q

Describe the characteristics of visceral pain

A

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

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

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

26
Q

What are Dermatomes?

A

“Dermatomes” are the regions of the body sending somatic afferents to each spinal cord segment