Learning Objectives (NON-CLIC) Flashcards
What is the purpose of emesis?
Describe the physiological control of vomiting and gut motility
Defense mechanism
List different emetic stimuli.
Describe the physiological control of vomiting and gut motility
- Blood
- Intestine
- Neural input from GI tract, labyrinth, and CNS
What are the two units that are make up the central neural regulation system of vomiting? And where are they located?
▪ Located in the Medulla
▪ The Vomiting (emetic) centre
▪ The Chemoreceptor Trigger Zone, (CTZ)
A) Describe the vomiting centre.
B) Describe the chemoreceptor trigger zone.
A)
▪ Collection of multiple sensory, motor and control nuclei
▪ Mainly in the medullary and pontile reticular formation
▪ Receives impulses from both vagal and sympathetic afferent nerves
▪ Responds to the incoming signals to coordinate emesis
B)
▪ Sensitive to chemical stimuli
▪ Main site of action of many emetic and antiemetic drugs (because CTZ is in an area where the BBB is relatively permeable
▪ Mediates motion sickness (due to various movements with the stimuli being the vestibular apparatus)
List the various stimuli of nausea vomiting.
- Pain, repulsive sights and smells, and emotional factors travel from higher cortical centres to the vomiting centre
- Stimulation of the sensory nerve endings in the stomach and duodenum through vagal afferents straight to CTZ
- Or toxins/toxic chemicals which is sensed by enterochromaffin cells and released 5-HT up the vagal afferent nerves to CTZ then to vomiting centre
- Disturbance of the vestibular apparatus (e.g. motion sickness) where stimuli from labyrinth -> vestibular nuclei -> CTZ -> vomiting centre)
Describe the stages of vomiting.
- Nausea - feeling of wanting to vomit, associated with autonomic effects like salivation/pallor/sweating
- Retching - strong voluntary effort to vomit with no actual vomiting (unproductive)
- Vomiting - Expulsion of gastric contents thought the mouth
What type of vomiting do esophageal varices and peptic ulcer cause?
▪ Hematemesis - vomiting fresh blood or altered blood (altered = ‘ground coffee’ look as they are further down in the GI tract and hence the blood has gone some changes on the way, can be indicative of a serious bleed)
Other than hematemesis, name two other types of vomiting. Provide examples of underlying causes of each.
▪ Projectile vomiting - example: gastric outlet or upper GI obstruction
▪ Early-morning vomiting - examples: pregnancy, alcohol dependency, metabolic disorder (E.g. uremia)
What are two factors that need to be considered when prescribing anti-emetics?
▪ Cause of vomiting must be known to prescribe (better to treat the cause of the vomiting if possible)
▪ Drug must be chosen based on where it acts, and the source of the stimuli
A pregnant woman with hyperemesis gravidarum requires management. What are some of the considerations when using anti-emetics in pregnancy?
▪ Benefit: Risk ratio (to mother and fetus)
▪ Try and avoid giving any in the first trimester if possible
List 4 types of anti-emetic medications based on their mechanism of action. (Most commonly used in primary and secondary care)
▪ Antimuscarinics (M1)
▪ Antihistamines (H1)
▪ Dopamine antagonists (D2)
▪ 5HT3 Antagonists
One type of antiemetics is antimuscarinic drugs.
A) Name the location of muscarinic receptors where these drugs will act.
B) Name an example of an antimuscarinic anti-emetic drug.
C) Name a common presentation that the example in (B) usually used for in primary care.
D) Name 4 side effects of antimuscarinic drugs.
A) Vestibular nuclei which receives impulses from the inner ear
B) Hyoscine Hydrobromide (caution in epilepsy)
C) Motion sickness (available in tablets or patches)
D) Dry mouth, blurred vision, hot/flushed skin, bradycardia followed by tachycardia
Another type of antiemetics are antihistamines (H1 Receptors antagonists).
A) State the situations in which these are most useful.
B) List some of the side effects of antihistamine medications.
C) Provide 3 examples of antihistamine antiemetic medications.
A) Good for numerous causes of N/V. Especially if someone has a generic type not associated with a specific diagnosis: including motion sickness + stomach irritants
B) Drowsiness, antimuscarinic effects
C)
• Cinnarizine (Particularly good for vestibular disorders and motion sickness rather than generic N/V , contraindicated in acute prophyria, SE: drowsiness, Nausea, weight gain)
• Cyclizine (Generic N/V, motion sickness, vestibular disorders, and good for palliative care, contra in severe liver disease, SE’s: Angle closure glaucoma, depression, drowsiness)
• Promethazine (N+V, motion sickness, labyrinthine disorder and particularly goo din severe morning sickness, contra in under 2yo, SE’s: drowsiness, anxiety, dry mouth)
Another type of antiemetic medications are dopamine antagonists. List three examples of dopamine antagonists, with brief description of indications, contraindications and SE examples.
Examples:
- Phenothiazines - mainly with severe N+V related to cancer radiation therapy (E.g prochlorperazine)
- Domperidone - N + V associated with cytotoxic causes and GI causes
- Metoclopramide - N + V, N + V associated with migrane/ehcmo, radio t
(For details on the rest check lecture LO 1 Week 7)
One type of antiemetics is 5HT3 antagonists drugs.
A) Name the location of receptors where these drugs will act.
B) Name an example of 5HT3 anti-emetic drug.
C) Name a common presentation that the example in (B) usually used for in primary care.
D) Name side effects of these drugs.
A) Prime site of action is CTZ
B) Ondansetron (contraindicated in long qt syndrome) - drugs generally end with ansetron
C) Particularly useful in managing N/V in patients receiving cytotoxic, radiation therapy and in post operative N/V
D) Can get headaches and GI upsets but generally uncommon
A) Describe the neuronal control of GI tract.
B) Describe the hormonal control of the GI tract.
A)
▪ Parasympathetic nerves increase activity of enteric nervous system (increase smooth muscle tone, promote sphincter relaxation)
▪ Sympathetic Inhibits the activity
▪ There are two plexuses which are controlled by parasympathetic and sympathetic nerves:
○ Myenteric plexus (out plexus) - increased tone of gut wall, increase strength of contraction, increase rate of contractions, inhibits pyloric, ile1
○ Submucosal plexus (inner plexus)
B)
▪ GI hormones exert effects of target cells: secretin, gastrin, cholecystokinin, somatostatin
List the different types of laxatives.
- Bulk-forming laxatives (Bulk-fibre provides increased volume and promotes peristalsis by distention)
- Stimulant laxatives
- Faecal softeners (coats and breaks up particles)
- Osmotic laxatives (draw water out, liquid mixes with stool to soften)
Name a Bulk-forming laxative.
Ispaghula husk
Name a stimulant laxative.
Senna (not good if someone has cramps already)
Name a softner laxative.
Docusate (for chronic constipation)
Name a osmotic laxative.
Lactulose
What is the basic pathophysiology of diarrhoea.
Diarrhoea involves both an increase in the motility of the GI tract and a decrease in the absorption of fluid and thus a loss of electrolyte.
Describe the approach to the treatment of acute diarrhea.
- Maintenance of fluid and electrolyte balance e.g. oral rehydration preparation
- Antimotility drugs (Loperamide ie imodium)
- Antispasmodics (reduce smooth muscle tone) e.g. hyoscine butylbromide (buscopan), mebeverine
- Occasionally antibacterial agent is indicated e.g. systemic bacterial infection, campylobacter enteritis, shigellosis and salmonellosis
A) What is Buscopan?
B) What is it used for?
A) Anti-Muscarinic, relaxes intestinal spasm (its called hyoscine butyl-bromide)
B) GI/GU spasms, irritable bowel and acute diarrhoea, and acute spasms + palliative care for excess respiratory secretions)