Symptoms of GI disease: nausea, vomiting and pain Flashcards
Why is nausea a sensation?
- personal, self-reported
- associated with physiological changes - we can sometimes tell
- unpleasant avoidance/aversion
Describe the premise of vomiting (emesis)?
- expels contents of upper GI tract via the mouth
- forceful (cf regurgitation, reflux)
- complex, co-ordinated reflexive events
- associated with sensation of relief
What is the relationship between vomiting and nausea?
- 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
What causes nausea and vomiting?
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What is the advantage of vomiting and nausea?
- Poisoning
- Obstruction
- Excessive alcohol
- Excessive eating
How are taste and smell involved in protecting us against toxins?
This is the first line of defence
- 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
How are gastric and upper GI afferents involved with protecting us against toxins?
This is the second line of defence
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
How does the Chemoreceptor Trigger Zone protect us against toxins?
This occurs when the toxins are absorbed into the blood stream
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
How does the Vestibular system protect us against toxins?
Where are they found and what do they do?
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
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
• 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
What are our anti-poison defences are coordinated by?
Nucleus Tractus Solitarius (NTS)
Where is the Nucleus Tractus Solitarius (NTS) found?
Found in the medulla of the brainstem
What does the NTS integrate?
It also integrates cardiac, respiratory and gastrointestinal functions
What four different warning inputs activate the NTS?
First input
- Visceral afferents that run via parasympathetic nerves through the vagus into the brainstem - caused by toxins, irritants, inflammation and distension
What is the area postrema and what does it control?
What is the second input that activates the NTS?
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.
What does the Vestibular system do?
The third input to the NTS
The organ of balance, inner ear
Detects toxins in the blood and motion sickness
What do higher centres do?
The fourth input to the NTS?
- things that have made you sick in the past
- other people in your group being sick
Somone sick makes you sick
Summarise the 4 inputs we have described and the outputs
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Describe the mechanisms of nausea
Mediated by the parasympathetic nervous system
- Reduced mixing and peristalsis
• prevents toxins from being carried further through the system
Getting rid of stuff in the stomach and small intestine - Proximal stomach relaxes
• prepares stomach to receive additional contents - Giant retrograde contraction
• sweeps up from mid-small intestine
• returns upper intestinal contents to stomach
Describe the mechanisms of vomiting
What are they mediated by?
- 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
- Vomiting (emesis)
oesophageal sphincters and crural diaphragm relax
further waves of contraction expel stomach contents
Mediated by the somatic nerves
What receptors mediate viseral pain?
what do they cause?
Nociceptor receptors - these run through the sympathetic nerves into the thoracic segments
They produce pain
What do pain receptors respond to?
Respond to “noxious” stimuli, and are called “nociceptors”
They respond to:
- Distension - the receptors fire more with greater distention
- Inflammation - Nociceptors respond to inflammatory mediators, as well as stretching of the gut wall:
injury irritants toxins infection autoimmunity
3 Muscle spasm
What does the release of pro-inflammatory chemicals from nociceptors cause?
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
What causes pain to be felt in the correct regions of the body and not in the correct regions?
- Somatic nociceptive endings are found within the skin
- Activation of these receptors activates the somatosensory cortex (in the cerebral cortex) via the spinal cord
- Stimulation of this coordinates the pain to the correct region of the body
- Other pain receptors can link to this pathway so pain is felt somewhere else e.g oesophageal nociceptor, occurs in wide area
Describe the characteristics of visceral pain
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
What are Dermatomes?
“Dermatomes” are the regions of the body sending somatic afferents to each spinal cord segment
