Pharmacology Of The Lower GI Tract Flashcards
Emesis physiology
Discomfort, dry mouth (salivary inhibition) Yawning (sympathetic distress) Reappearance of saliva Pyloris closes Tone of stomach increases Deep breath Contraction of abdominal muscles Forced expiration
Emesis neurology
Visceral afferent 5HT3 receptors detect stimulation of stomach/pharynx and toxins
Stimulate H1 and M receptors in nucleus of solitary tract
Stimulate vomiting centre M receptors
Nervous output
Toxins and 5HT3 receptors can also stimulate chemoreceptors
Trigger zone D2 and 5HT3 receptors-> vomiting centre
Motion sickness neurology
Motion detected by labyrinth
Stimulates vestibular nuclei H1 and M receptors
Stimulates chemoreceptors that trigger zone D2 and5Ht3 receptors
Etc
H1 receptor antagonists
Anti emetic Promethazine, cyclizine Act on vestibular nuclei-> effective in motion sickness Also have anti muscarinic effects Used in pregnancy
Anti muscarinic agents
Anti emetic
Hyoscine
Effective in motion sickness and stomach irritation
Anti muscarinic side effects
Dopamine antagonists
Anti emetic
Mentocloperamide
Acts in CT 2 but has unwanted side effects in CNS
effective against anti cancer drug induced Emesis
5-hyroxytryptamide antagonists
Anti emetic Ondansetron,Metocloperamide Block 5-HT3 receptors in gut and CNS Particularly effective against anti cancer drugs Post pop nausea
Diarrhoea
> 3 watery stools per day or 209g of stool per day, Bristol stool scale
Causes:
Rotavirus-> damages small bowel villi
Invasive bacteria->damage epithelium
Cytotoxins->damage mucosa
Adhesive enterotoxigenic bacteria-> adhere to brush border-> increase cAMP-> Cl and Na secretion followed by water
May be secondary to drugs
Antibiotics can cause super infection-> by increased chance of colonisation by pathogenic bacteria
Oralistat-> inhibits pancreatic lipase-> steatorrhea
Misoprostol->uncertain, inflammatory type response
PPI’s-> infection
Diarrhoea treatment
Oral rehydration therapy-> solution of electrolytes to replace loss! must be isotonic
Contains glucose for Na transport
Antibiotics-> of little value, normally viral
do a stool sample to identify bacteria first
Ciproflaxin for travellers diarrhoea
Probiotics-> reduce duration of diarrhoea infection
Anti motility agents, opioids
Codeine and loperamide
Reduce tone and peristaltic movement of GI muscle-> increased transit time-> promotes water reabsorption
Presynaptically inhibit release of ACH
Act on u receptors on presynaptic nerve->inhibit ACH
Cause K efflux-> hyper polarisation-> no Ca influx
Symptomatic relief but not cure
Loperamide doesn’t cross blood brain barrier and is enterhepaticly recycled so retained in gut
Antimotilty agents, antimuscarinics
Dicylorerine
Tricyclic antidepressants->anti muscarinic side effect
Act on muscarinic receptors in gut
Constipation
Less than 3 poos per week
Try balanced diet with lots of roughage first
May be drug induced
Osmotic laxatives
Lactulose->enters colon unchanged-> converted by bacteria-lactic and acetic acid-> increase fluid volume through osmosis
Macrogls
Magnesium
Laxative
Osmotic effect to increase fluid volume
Also realises CCK-> stimulates gut motility
Bulking agents
Laxative
Speed up small intestines and colon transit time
Ispaghulla
Methyl cellulose
