Nausea, Vomiting & Pain Flashcards
What is nausea?
Nausea is a sensation of feeling sick
What does nausea trigger?
Triggers aversion
What does vomiting expel?
expels contents of upper GI tract via mouth
What is both nausea and vomiting produced by?
Nausea is produced by the same stimuli as vomiting
What is nausea in relation to vomiting?
Nausea is generally a prodrome (ie premonitory symptom) of
vomiting
What are the different protections against ingested toxins?
- Taste and smell
- Gastric and upper GI afferents
- Chemoreceptor trigger zones
- Vestibular system
- Experience
What are the chemoreceptor trigger zone to protect against ingested toxins?
- the area postrema in the brainstem
- chemoreceptors that can detect toxins in the
blood
What is the vestibular system?
the organ of balance, but also a potent
trigger for emesis
What does poisoning produce in the vestibular neural pathways?
poisoning is thought to produce aberrant
activity in vestibular neural pathways
What coordinates nausea and vomiting?
Nucleus tractus solitarius(NTS)
Where is the NTS found?
Found in the medulla of the brainstem
How many different types of warning does the NTS receive and what are they?
- Visceral afferents for nausea and vomiting(parasympathetic)
- Area postrema(chemoreceptive trigger zone)
- Vestibular system
- Higher brain centres
How does the visceral afferent for nausea and vomiting warn the NTS?
-Afferent signals like toxins and irritants stimulate vagus afferent nerves in stomach and duodenum which send signals to the NTS
How does the area postrema warn the NTS?
-Detects toxins in blood as there is no blood-brain barrier
How does the vestibular system warn the NTS?
Toxins from the blood, un-natural movement triggers cranial nerve 8 which alerts the NTS
How does higher brain centres alert NTS?
-Things that your social group find disgusting
-Other people in your group being sick
-Things that made you sick in the past
What does the outputs from the NTS do the hypothalamus do?
↑ antidiuretic hormone (ADH; vasopressin)
What does the outputs from the NTS do to the higher centres?
nausea,
future avoidance
What does the outputs from the NTS do to autonomic efferents?
-changes in gut motility
-↑ salivation, vasoconstriction in GIT
How does the NTS trigger nausea?
- Reduced mixing and peristalsis
* prevents toxins from being carried prevents toxins from being carried
further through the systemfurther through the system - Proximal stomach relaxes2. Proximal stomach relaxes
* prepares stomach to receive
additional contents - Giant retrograde contraction3. Giant retrograde contraction
* sweeps up from mid-small intestine
* returns upper intestinal contents to
stomach
How does the NTS trigger vomitting?
- Retching (dry heaves)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 - Vomiting (emesis)Vomiting (emesis)
* oesophageal sphincters and crural
diaphragm relax
* further waves of contraction expel
stomach contents
How do the visceral afferents work for pain sensation?
- Damaging events cause afferent signals
- Signals from the stomach and lower esophagus are transmitted via the sympathetic greater splanchnic nerve at T1-9
- Signals from the small intestine, descending colon and sigmoid colon via the lesser splanchnic nerves at T10-T12
What are nociceptors?
Receptors in the pain pathways respond to “noxious” stimuli, and
are therefore called “nociceptors”
What are examples of noxious stimuli?
- distension
- inflammation
- muscle spasm
What is the response of nociceptors to stretching of the gut wall?
As gut distention increases, pain increases
What do nociceptors respond to?
Nociceptors respond to inflammatory mediators, as well as
stretching of the gut wall:
-injury
-toxins
-infection
What do nociceptors release and what feedback loop does this create?
- Nociceptors also release chemicals that increase
inflammatory responses - This creates a positive feedback loop, that may become self-sustaining
What is thought to occur in GI disease in regards to visceral pain pathways?
Chronic sensitisation of visceral pain pathways is thought to
occur in GI disease
How are somatic pain pathways organised?
Somatic pain
pathways are precisely
organised
How are visceral pain pathways organised and what can this cause?
Visceral pain pathways piggy-back onto somatic
pathways. Hence why this can cause referred pain.
What is visceral pain referred to and what is this due to?
Generally “referred” to regions of the body wall
- due to viscero-somatic convergence
Why does visceral pain often diffuse and poorly localized?
- relatively small number of afferents
- imprecise wiring
What does each organ have a characteristic pattern of in visceral pain and what can this evolve to?
Each organ has a characteristic pattern of referral
- initially to dermatomes matching the embryonic origin of the organ
- but may evolve as neighbouring tissues are affected
