Pharmacology Of The Lower GI Tract Flashcards Preview

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Flashcards in Pharmacology Of The Lower GI Tract Deck (23):
0

Emesis definition and causes

Appropriate or inappropriate gastric emptying
Stimulated by:
Toxins
Motion sickness
Smells
Migraines
Oregnancy

1

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

2

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

3

Motion sickness neurology

Motion detected by labyrinth
Stimulates vestibular nuclei H1 and M receptors
Stimulates chemoreceptors that trigger zone D2 and5Ht3 receptors
Etc

4

H1 receptor antagonists

Anti emetic
Promethazine, cyclizine
Act on vestibular nuclei-> effective in motion sickness
Also have anti muscarinic effects
Used in pregnancy

5

Anti muscarinic agents

Anti emetic
Hyoscine
Effective in motion sickness and stomach irritation
Anti muscarinic side effects

6

Dopamine antagonists

Anti emetic
Mentocloperamide
Acts in CT 2 but has unwanted side effects in CNS
effective against anti cancer drug induced Emesis

7

5-hyroxytryptamide antagonists

Anti emetic
Ondansetron,Metocloperamide
Block 5-HT3 receptors in gut and CNS
Particularly effective against anti cancer drugs
Post pop nausea

8

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


9

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

10

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

11

Antimotilty agents, antimuscarinics

Dicylorerine
Tricyclic antidepressants->anti muscarinic side effect
Act on muscarinic receptors in gut

12

Constipation

Less than 3 poos per week
Try balanced diet with lots of roughage first
May be drug induced

13

Osmotic laxatives

Lactulose->enters colon unchanged-> converted by bacteria-lactic and acetic acid-> increase fluid volume through osmosis
Macrogls

14

Magnesium

Laxative
Osmotic effect to increase fluid volume
Also realises CCK-> stimulates gut motility

15

Bulking agents

Laxative
Speed up small intestines and colon transit time
Ispaghulla
Methyl cellulose

16

Stimulant laxatives

Senna extracts
Enter colon-> metabolised-> anthracem derivatives-> stimulate gut motility
Danton, irritant

17

Irritable bowl syndrome

Present for at least 3 days pert month in the last 3 months
Abdo pain
Bloating-> relieved by defection
Changes in bowl habit
Episodes of diarrhoea and or consitpation

18

IBS treatments

Lactulose or loperamide for symptoms
Antispasmodic agents:
antimuscarinics
mebervine (OCT)-> direct relaxant of GI smooth muscle
Amitriptyline:
Low dose
Provides some pain relief
Antimuscarinic effects
Alters sensitivity of nerves in low GI

19

Inflammatory bowel disease

Chrons-> mouth to anus
Pain and bloody diarrhea
Ulcerative colitis->rectum to colon

20

IBS treatment
5-ASA's

5-amionosalicylates:
Mainly for UL
Sulphosalazine-> metabolised in colon by gut flora-> 5-amionosalicylates and sulphapyridine
5-ASA-> inhibits leukotriens and prostanoid formation-> scavenge free radicals-> decrease neutrophil chemo taxis

21

IBD treatment,corticosteroids

Induce remission of IBD
Prednisone-> glucocorticoid with anti inflammatory immunosuppressive actions
Budesonide-> poorly absorbed-> less side effects

22

Other IBS treatment

Bowel rest
Probiotics
Fish oils
Immunosuppressants->azathicprine, cyclosporine
Methotrexate for severe chrome