Nausea, vomiting and pain Flashcards
(21 cards)
Explain characteristics of nausea and vomiting
Nausea:
-personal, self reported
-associated with physiological changes
-unpleasant
-triggers aversion
Vomiting:
-expels contents of upper GI tract via mouth
-forceful
-complex, co-ordinated reflexive events
-associated with sensation of relief
What is the relationship between nausea and vomiting
-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?
-food poisoning
-GI infection
-excessive alcohol
-pregnancy
-excessive eating
-travel sickness
-metabolic disturbance
-emotional upset
-GI disease
-drugs
-other people being sick
Explain protection against ingested toxins
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
Explain Gastric and upper GI afferents
-can potentially expel harmful agents before they have much chance to be absorbed
-associated with chemoreceptive cells that respond to:
-naturally occurring toxins
-damaging chemicals
-inflammatory mediators
*but non ingested toxins will have the same effect (e.g chemotherapy, systemic infection, metabolic disturbance)
Explain the chemoreceptor trigger zone
-the area postrema in the brainstem
-blood-brain barrier is leaky
-chemoreceptors that can detect toxins in the blood
Explain the vestibular system and the prevention of ingestion (learning and aversion)
Vestibular system:
-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 unnatural motion
Prevention of ingestion- learning and aversion:
-if we survive a mistake we avoid repeating it.
-aversion may hard-wire avoidance
-but we can create incorrect associations
Explain the mechanisms of nausea and vomiting
-our anti poison defences are coordinated by the nucleus tractus solitarius (NTS)
-found in the medulla of the brainstem
-it also integrates cardiac, respiratory and GI functions
Explain how it receives 4 different types of warning inputs
1) Visceral afferents (N & V):
Something happens in your gut: Maybe you ate something that caused irritation, or your stomach is stretched.
Sensory nerves notice: Special nerves in your gut, called “visceral afferents” (specifically the vagus nerve for the upper gut and other nerves for the lower gut), detect these changes like toxins, irritants, stretching, or inflammation.
Signals to the brain: These nerves then send signals up to your brainstem (specifically to an area called the NTS).
Brain processes: Your brain then processes these signals. This can lead to various responses, like feeling full, nauseous, or having pain.
2) Area postrema:
-This area is located in your brainstem (the lower part of your brain).
It’s special because it doesn’t have a strong barrier like other parts of your brain (this is labeled “no blood-brain barrier”).
Because of this, it can directly sense things in your blood, like toxins.
If it detects something harmful in your blood, it can trigger a response, often vomiting, to get rid of the toxins.
3) Vestibular system:
-Your inner ear has structures that sense movement and help you stay balanced.
Sometimes, problems in the inner ear or confusing signals it sends to the brain can lead to feelings of dizziness and nausea (motion sickness is an example of this).
-The diagram shows that if there are “toxins from the blood” affecting this area (though this is less common for typical motion sickness), it can also disrupt the signals sent through a nerve called CN8 (vestibulocochlear nerve).
These disrupted signals can then contribute to the sensation of being sick.
4) Higher centres:
-things that your social group find disgusting
-other people in your group being sick
-things that have made you sick in the past
Explain inputs to the NTS
Think of the NTS as a central processing station that receives different kinds of “sick signals”:
From your gut (abdominal afferents via the vagus nerve): things like toxins, irritants, inflammation, or your stomach being too full (distension).
From the area postrema: this detects toxins directly in your blood.
From your balance system (vestibular system): if it’s disrupted, like with motion sickness.
From higher brain areas: things like bad memories, sights, or smells (prior experience, aversive stimuli) can also trigger it.
Explain how NTS triggers nausea and vomiting
Once the NTS is activated:
-It can send signals to other parts of the -brain, leading to the feeling of nausea and also influencing future avoidance of whatever made you sick.
-It can talk to the hypothalamus, which can release a hormone called ADH/vasopressin.
It sends signals through autonomic nerves, which can cause things like:
Changes in how your gut moves (reduced mixing and peristalsis).
Increased salivation and blood vessel changes (vasoconstriction) in your gut.
Explain more about how NTS triggers nausea and vomiting
1) Reduced mixing and peristalsis:
-prevents toxins from being carried further through the system
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
Explain mechanisms of nausea and vomiting
1) 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
2) Vomiting (emesis):
-oesophageal sphincters and crural diaphragm relax
-further waves of contraction expel stomach contents
Explain visceral afferents (pain)
Something damaging happens: Inside your body, like in your stomach or intestines, there might be a “damaging event”.
Pain nerves are activated: Special pain-sensing nerves called “visceral afferents” detect this damage.
Signals to the spinal cord and brain: These nerves send pain signals along different pathways up to your spinal cord and eventually to your brain.
You feel pain: Your brain interprets these signals as pain coming from that specific area of your body.
Explain receptors for visceral pain
-‘pain’ receptors respond to ‘noxious’ stimuli —> are called ‘nociceptors’
They respond to:
-distension
-inflammation
-muscle spasm
Explain nociceptors
-Nociceptors respond to inflammatory mediators as well as stretching of the gut wall:
-injury
-irritants
-toxins
-infection
-autoimmunity
Explain chronic sensitisation of visceral pain pathways is thought to occur in GI disease
-inflammation depolarises these nociceptors
-when depolarised they release pro-inflammatory chemicals
-this positive feedback increases responses which can in turn potentiate synapses
-leading to potentially self sustaining activity that persists beyond the original cause
Explain somatic pain
somatic pain is precisely located
Explain viscero-somatic convergence
-The diagram shows a signal coming from a pain receptor in your esophagus (an internal organ - “oesophageal nociceptor”).
It also shows a signal coming from a pain receptor in your skin or muscle (“somatic nociceptor”).
These two different pain signals can sometimes converge or meet up at the same place in your spinal cord on their way to your brain’s somatosensory cortex (the area that processes touch and pain).
Because these signals meet up, your brain can sometimes get confused and think the pain is coming from the skin or muscle area instead of the internal organ.
Describe how each organ has a characteristic pattern of referral
-afferents synapse in segments matching the embryonic origin of each organ
-infections in the gall bladder often spread to the parietal peritoneum and diaphragm
explain characteristics of visceral pain
-generally referred to regions of the body wall due to viscera-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
