GI Motility [2]

Question 1

4 components in gastric anatomy

Answer 1

Fundus
Main body
Atum
Sphincter

Question 2

What control frequency of gastric contractions

Answer 2

Pacemaker cells in upper fundus
- create electrical rhythm and partial depolarisation
- contraction when slow wave exceeds resting membrane potential

Question 3

What controls force of gastric contraction (2)

Answer 3

Neural
- increased by vagal activity
- decreased by adrenergic activity
Hormonal
- increased by Gastrin from amino acids in good
- decreased by secretin

Question 4

Process of ‘receptive relaxation’
- response to intake of food

Answer 4

Stretch receptors
Activation of vagal inhibitory neurones
Relaxation of smooth muscle
Little changes in pressure

Question 5

2 centres that control emesis

Answer 5

Vomiting centre
Chemoreceptor trigger zone (CTZ)

Question 6

What causes emetic effect

Answer 6

Irritant effects of alkaloids emetine & cephaeline

Question 7

4 anti emetics

Answer 7

H1 receptor antagonists
Muscarinic antagonists
D2 receptor antagonists
5 - HT3 receptor antagonists

Question 8

Describe H1 receptors antagonists and example

Answer 8

For motion sickness
Given before nausea
Act on vestibular nuclei
E.g cyclizine

Question 9

Describe Muscarinic antagonists and example

Answer 9

For motion sickness
Effective against vestibular & local gut stimuli
Less sedation that H1
May interact with physiological systems as it blocks sympathetic and parasympathetic pathways
Eg hyoscine

Question 10

Describe D2 receptors antagonists and example

Answer 10

For vomiting caused by renal failure and radiotherapy
Work on the CTZ
Has CNS effects - twitching
Prolactin stimulation - menstrual disorders
Eg metoclopramide

Question 11

Describe 5 - HT3 receptor antagonists and example

Answer 11

For chemotherapy and post surgery nausea
Act of CTZ
For very severe sickness
Eg ondansetron

Question 12

Causes of diarrhoea (4) + examples

Answer 12

Viral - rotavirus
Bacterial - campylobacter
Systemic disease - inflammatory bowel disease
Drug induced - antibiotic

Question 13

How do anti- diarrhoeals work (4)

Answer 13

1. Stimulate opiate receptors
2. Increase muscle tone - more rigid
3. Suppress propulsive peristalsis
4. Reduces sensitivity to rectal distension

Question 14

Example of anti- diarrhoeal and mechanism

Answer 14

Opioid agonists (analgesic - codeine)
- acts on mu receptors in myentric neurones
- hyperpolarisation
- inhibits Ach release
- reduces bowel motility

Question 15

4 drugs for constipation (laxatives)

Answer 15

Bulk forming agents
Osmotic laxatives
Stimulants
Faecal softeners

Question 16

Describe bulk forming agents and example

Answer 16

Contain polysaccharide and cellulose
- not digested so retain fluid
12-36 hour action
Cause flatulence & bloating
Bran and methylcellulose

Question 17

Describe osmotic laxatives and example

Answer 17

Let water into faecal matter by osmosis
Work quicker than bulk forming
Cause abdominal cramps and flatulence
Magnesium salts

Question 18

Describe stimulants and example

Answer 18

Stimulate colonic nerves
Reduces transit time
8-12 hour action
Cause colonic atony (unable to stimulate itself on its own)
Senna

Question 19

Describe faecal softeners and example

Answer 19

Coat stool in non-ionic surfactant
Reduces surface tension
Penetration of fluid into faecal mass
Docusatesodium

Question 20

2 inflammatory bowel diseases

Answer 20

Crohn’s disease (entire gut)
Ulcerative colitis (only large bowel)

Question 21

Treatment of inflammatory bowel disease

Answer 21

Glucocorticoids
Aminosalicylates