Nausea, Vomiting and Pain Flashcards
What is vomiting?
Vomiting (emesis) is a physical act:
- 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 (premonitory symptom) of vomiting
Nausea may clear up w/o triggering vomitingAND vomiting can occur w/o prior nausea- eg sticking finger down throat
List some causes of nausea and vomiting
Why can obstruction cause vomiting?
Si hay obstruction in your intestines, hay que remove as much of the contents of your GI tract bc peristalsis will keep pushing that stuff down there.
Your intestine wont be able to pass contents down so it will expand
It will stretch its walls and be v painful- could do a lot of damage.
How does our taste and smell protect us from toxins?
How do our gastric and upper GI afferents protect us from toxins?
Gastric & upper GI afferents can expel harmful agents before they’re absorbed
They’re associated w chemoreceptive cells that respond to:
naturally occurring toxins
damaging chemicals
inflammatory mediators
why do some non ingested toxins, eg chemotherapy produce the vomiting reflex?
Chemoreceptor cells sit in the gut wall in tissue w good blood supply.
Substances mix from capillaries into the ECF that surrounds those key receptive cells.
So substances circulating in the blood can trigger responses from these cells which trigger responses from the efference. This produces the vomiting reflex.
How does the chemoreceptor trigger zone protect us from toxins?
Chemoreceptor Trigger Zone
Found in the area postrema in the brainstem. Here the blood-brain barrier is “leaky”, so toxins can enter
Hay chemoreceptors that can detect toxins in the blood
BUT again non-ingested toxins will have the same effect – eg chemotherapy, systemic infection, metabolic disturbance
How does the chemoreceptor trigger zone protect us from toxins?
Chemoreceptor Trigger Zone
Found in the area postrema in the brainstem. Here the blood-brain barrier is “leaky”, so toxins can enter
Hay chemoreceptors that can detect toxins in the blood
BUT again non-ingested toxins will have the same effect – eg chemotherapy, systemic infection, metabolic disturbance
How does the vestibular system protect against toxins?
Vestibular system is the organ of balance, but also a potent trigger for emesis
Poisoning produces aberrant activity in vestibular neural pathways:
Axons from the receptors are sent out through the 8th cranial nerve (vestibulocochlear nerve) and straight into the NTS
BUT also triggers nausea and vomiting in response to un-natural motion
How does learning and aversion protect us from toxins?
If we survive a mistake we avoid repeating it (unpleasantness reinforces learning)
Aversion may hard-wire avoidance
BUT can create incorrect associations
Describe visceral afferents
Visceral afferents are the sensory nerves that run up into the brainstem.
They get their input from chemoreceptor cells found in the walls of the stomach and the top of the small intestine.
Chemoreceptors respond to toxins, irritants, inflammatory mediators.
Also hay some afferent nerves that have endings that respond to abnormal distension of the GI tract.
How does increased intracranial Pa cause nausea and vomiting?
If intracranial Pa goes up, the brain swells. Extra volume gets squeezed out through the foramen magnum. The brain gets pressed down into area prostrema and the nucleus tractus solitarius.
Those areas cause aberrant signals that will trigger nausea and vomiting.
What is the mechanism of nausea and vomiting?
Our anti-poison defences are co-ordinated by the Nucleus Tractus Solitarius (NTS)
Found in the medulla of the brainstem, it also integrates cardiac, respiratory and gastrointestinal functions
Describe the higher centre input for n+v