GI pharmacology

Question 1

Describe the layout of the enteric nervous system

Answer 1

Myenteric plexus
Submucosal plexus

Question 2

Describe the neuronal control of the GIT

Answer 2

Parasympathetic from vagus
- cholinergic and excitatory
Sympathetic fibres are post-ganglionic to:
- BVs
- smooth muscle
- glands
- inhibit acetyl choline release from plexuses

Question 3

Describe the hormonal control of the GIT

Answer 3

Endocrine - peptides from mucosa (gastrin, CCK)
Paracrine - local regulatory peptides (+ histamine)

Question 4

What is gastric secretion made up of?

Answer 4

acid
bicarbonate
mucous

Question 5

In what ways can gastric secretion be modified?

Answer 5

Neutralisation
Mucosal protection
Absorbents
Histamine antagonists
Proton pump inhibitors
Misoprostol

Question 6

What can be used to neutralise stomach acid?

Answer 6

Weak bases:
- Magnesium hydroxide and trisilicate
- Aluminium hydroxide gel
- Alginates and simeticone

Question 7

What conditions can be managed by neutralising gastric secretion?

Answer 7

• ruminal acidosis
• gastritis
• oesophagitis

Question 8

What can be used for mucosal protection in gastric secretion modification - what is the clinical relevance of this?

Answer 8

Sucralfate (disaccharide)
- may prevent uptake of other drugs

Question 9

What is the function of adding absorbents to gastric secretion?

Answer 9

Coating actions
Bind bacteria and toxins

Question 10

What absorbents can be added to gastric secretion?

Answer 10

Activated charcoal
Bismuth
Kaolin (aluminium silicate)/pectin

Question 11

What is the action of adding histamine antagonists in gastric secretion

Answer 11

Inhibits gastrin, histamine and acetylcholine stimulated secretion
Pepsin secretion falls (less volume of fluid)
Get a rebound increase on withdrawal

Question 12

What histamine antagonists can be added to gastric secretion?

Answer 12

Ranitidine
Cimetidine

Question 13

what is the action of adding proton pump inhibitors to gastric secretion?

Answer 13

irreversibly bind to ATPase
Inhibits basal and stimulated release

Question 14

What proton pump inhibitors can be added to gastric secretion?

Answer 14

omeprazole
lansprazole

Question 15

What is the action of misoprostol when added to gastric secretion?

Answer 15

inhibits acid secretion
increases mucosal blood flow
Increases uterine contraction (don’t use in pregnant animals)

Question 16

What are the 2 centres that control emetics?

Answer 16

chemo receptor trigger zone (CRTZ)
Vomiting centre in brainstem

Question 17

what is the function of the chemo receptor trigger zone (CRTZ)?

Answer 17

chemical stimuli
BBB is permeable in area of CRTZ
Gets input from vestibular apparatrus (motion sickness)
Sends impulses to vomiting centre in brainstem

Question 18

What is the function of the vomiting centre in the brainstem?

Answer 18

coordinates and integrates vomiting

Question 19

Describe the pathophysiology of vomiting

Answer 19

Impulse to vomiting centre via central, peripheral pathways or vestibular apparatus => substance P (neurotransmitter) binds to NK-1 receptors at cell membrane => signal travels via vagus nerve to abdominal muscles + diaphragm => vomiting

Question 20

What substances are emetics?

Answer 20

Apomorphine:
- dopamine agonist
Alpha-2 agonists:
- xylazine)
Syrup of Ipecac:
- direct irritant
- causes cardiotoxicity in high doses

Question 21

what are some dopamine antagonists?

Answer 21

Phenothiazine derivatives e.g., chloropromazine
Metaclopramid
Domperidone

Question 22

Describe the action of metaclopramide and domperidone

Answer 22

Dopamine antagonists
Short action so need to infuse IV
Metaclopramide - centrally acting (CRTZ)
Domperidone - peripherally acting
Increase gastric emptying and increased motility
Do not use if vomiting due to obstruction (sends obstruction further down GIT)

Question 23

what are some anti-emetics drugs?

Answer 23

Dopamine antagonists
Cerenia (maropitant)
Anti-histamines
Anticholinergics
Cannabinoids

Question 24

Describe the action of cerenia (maropitant)

Answer 24

NK-1 antagonist
Competes with substance P

Question 25

How is diarrhoea managed?

Answer 25

maintenance of fluid balance: - IV fluid therapy (Hartmann's solution) - oral fluids - anti-infectives e.g., zinc = immune stimulant

Question 26

why may you want to modify intestinal motility?

Answer 26

reduce pain increase transit time and re-absorption 'window'

Question 27

What are the 2 main classes of spasmolytics (antimotility) drugs?

Answer 27

Opiates e.g., morphine, codeine and loperamide (immodium) Muscarinic antagonists e.g., atropine, hyoscine (buscopan)

Question 28

What is the action of morphine as a spasmolytic drug?

Answer 28

increases intestinal contractions but decreases propulsion increased large intestinal tone => constipation

Question 29

What is the action of muscarinic antagonists as spasmolytic drugs?

Answer 29

neuronal control inhibit acetylcholine stimulatory effects from vagus nerve

Question 30

what classes of drugs improve GIT motility?

Answer 30

Prokinetics - cisapride Laxatives

Question 31

What are some laxatives?

Answer 31

Saline and hyperosmotic agents Bulk producing agents irritants

Question 32

What is bulk and how does it improve aid intestinal motility

Answer 32

Methylcellulose Polysaccharide polymers not easily digested => forms hydrated bulk in gut Holds water and promotes peristalsis

Question 33

How do osmotic laxatives aid intestinal motility?

Answer 33

Poorly absorbed solutes Lactulose - broken down to lactic acid => lower pH => traps ammonia and water in gut => softens faeces => eases motility

Question 34

What is the pharmacological intervention used in idiopathic inflammatory bowel disease?

Answer 34

Anti-inflammatory steroids e.g., prednisolone sulphasalazine

Question 35

what is a pro-drug?

Answer 35

drug that is broken down into the active substance in the liver

Question 36

What is the treatment for frothy bloat in ruminants?

Answer 36

antifoaming agents Surfactants/detergents cause bubbles to break down

Question 37

what causes frothy bloat in ruminants?

Answer 37

clover