S1: Nausea, Vomiting and Pain Flashcards
What is nausea?
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
What is vomiting?
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
What is the medical name for vomiting?
Emesis
Is nausea produced by the same stimuli as vomiting?
Yes
Nausea is recognised as a prodrome. What does this mean?
Prodrome is a warning symptom
Nausea is therefore a warning symptom of vomiting
List some causes of nausea and vomiting
Poisoning Gastroenteritis Excessive alcohol Pregnancy Excessive eating Travel sickness Metabolic disturbances Drugs GI disease Emotional upset
What is the benefit to vomiting?
It acts as protection against ingested toxins
What is the first defence against ingested toxins?
Taste and smell
How does our body protect us from toxins - especially in children?
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
What happens when our body creates incorrect associations to stimulus?
People can feel nausea and vomit at normal stimuli e.g. seafood
Explain how our gastric and upper GI afferent fibres help prevent ingested toxins
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
Where is the chemoreceptors trigger zone?
The area postrema in the brain stem (medulla)
Explain the chemoreceptor trigger zone
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
What is the vestibular system?
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
What is the disadvantage with the vestibular system?
It triggers nausea and vomiting in response to unnatural motion e.g. on boat as it assumes that poison may have been ingested
Where is the nucleus tractus solitaries found and what’s its role?
It is located in the medulla of the brain stem and integrates cardiac, respiratory and gastrointestinal functions.
The NTS is the coordinator/regulator
Where do the abdominal afferents travel to?
The nucleus tractus solitaries by vagus nerve
Where are visceral afferent receptors found?
They are found in the fundus and duodenum
Examples of visceral afferents that can trigger nausea and vomiting
Toxins
Irritants
Distension
Briefly explain the pathway the visceral afferents take
The afferents take information via the vagus nerve (parasympathetic system)
Where do fibres from the vestibular system travel?
They travel to the NTS (nucleus tractus solitarius) after detecting toxins or disequilibrium
What do the fibres from the area postrema do?
They detect toxins in the blood
What reduces area postrema and abdominal afferent signalling to NTS?
5-HT3 antagonist
It reduces nausea and vomiting
Name 3 mechanisms of nausea
- Reduced gut motility (mixing and peristalsis) prevents toxins from being carried further through the system
- Proximal stomach relaxes to receive additional contents
- Giant retrograde contraction occurs, that sweeps up from the midsmall intestine and returns upper intestinal contents to stomach
Name the structure that the NTS signals to for nausea
Frontal cortex
What happens when NTS signals the hypothalamus?
The hypothalamus will release ADH which helps conserve water so less is lost during vomiting
What happens when NTS signals the the frontal cortex?
Nausea
What happens when NTS signals the autonomic efferents?
- Changes in gut motility
2. Salivation, vasoconstriction in GIT and skin, sweating
Name the 2 structures that the NTS signals to for vomiting
Autonomic efferents
Hypothalamus
Mechanism of vomiting
- 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
- Then is emesis. The oesophageal sphincters and crural diaphragm relax and further waves of contractions of the stomach expel stomach contents
How is the mechanism of vomiting different to nausea
In vomiting, NTS will use somatic and autonomic efferents to cause changes in gut motility and expulsion as well as salivation , vasoconstriction and sweating
What nerve innervates the abdominal muscle?
Somatic nerve
What nerve innervates the diaphragm?
Phrenic nerve
Name the 2 anti-reflux barriers
Oesophageal sphincters and crural diaphragm
What are sensory receptors for pain called?
Nociceptors
Name the 2 nociceptors in the GI
Arc stretch receptors
Chemoreceptors
Name some noxious stimuli
Distension Inflammation Ischaemia Traumatic injury Muscle spasm
Are most GI nociceptors afferent axons sympathetic or parasympathetic?
They mostly run in the sympathetic nerves (the greater and lesser splanchnic nerves)
Explain distension of the stomach
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.
Nociceptors respond to inflammatory mediators and produce some of their own.
What happens to the GI if cell receptors become hypersensitive due to inflammation?
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
Characteristics of visceral pain
- Diffuse and poorly localised
- Pain is generally referred to regions of the body wall
- Each organ has a characteristic pattern of referral
Explain how visceral pain is diffuse and poorly localised
There are relatively small number of afferents and there is diffuse innervation of organs.
The pathways are divergent
Explain how visceral pain is often referred to regions of the body wall
This is due to viscera-somatic convergence. This means that visceral afferents travel with somatic nerves which innervate a similar body wall
Explain how each organ has a characteristic pattern of referral for visceral pain
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
