Gut Motility

Question 1

Describe the physiology and pharmacology of acid secretion by the parietal cells

Answer 1

Secrete HCl, intrinsic factor
Histamine –> H2 receptor –> cAMP dependent (blocked by H2 receptor antagonist)
ACh –> M3 receptor –> Ca2+ dependent (blocked by muscarinic antagonist)
Gastrin –> CCK2 receptor –> Ca2+ dependent
H+/K+/ATPase –> acid (blocked by PPI)

Question 2

Understand the mechanism of action of the major drug groups used to control acid secretion and provide gastric protection

Answer 2

H2 antagonists - block H2 receptor, short half life (BD dosage), take as required
PPI - target ATPase, binds covalently to cysteines, acid activated, delayed response (max efficacy is 2-3 days later)

Question 3

Describe use of drugs within general management of GORD/oesophagitis

Answer 3

Symptom control - lifestyle, antacids/alginates, H2RA, PPI

Oesophagitis complications = Barrett’s oesophagus, cancer, peptic stricture, lifelong PPI

Question 4

Understand the role of helicobacter pylori in development of peptic ulcer disease

Answer 4

Infects antrum of stomach
Causes gastritis (often asymptomatic)
Gastritis may lead to gastric or duodenal ulcers due to increased acid production –> perforation

Question 5

Describe the treatment of H. pylori infection

Answer 5

Triple therapy:
Antibiotics x2 (clarithromycin, amoxicillin)
PPI (lansoprazole)

Question 6

List common drugs used to treat GORD

Answer 6

Antacids e.g. Rennie, Gaviscon
Alginates e.g. Sucralfate
H2RA e.g. Cimetidine, Ranitidine
PPI e.g. Omeprazole, Lansoprazole 
*ADR - diarrhoea

Question 7

Name three methods of controlling gut motility

Answer 7

Myogenic - rhythmic contraction, pacemaker from interstitial cells of Cajal
Neural - contraction, post ganglionic cholinergic
Hormonal - neurotransmitters, peptide hormones (e.g. gastrin, secretin, CCK, motilin, PGs)

Question 8

Describe the physiology of emesis

Answer 8

Pyloric (and nasopharynx) sphincters close while cardia and oesophagus relax
Contraction of abdominal wall and diaphragm propels gastric contents
Glottis closes with elevation of soft palate

Question 9

Describe the process of nausea

Answer 9

Causes - pregnancy, medications, toxins, pain, irradiation, smells, high ICP, rotational movement
–> vomiting centre in medulla (chemosensory trigger zone) –> priliminary signs (salivation, retching, dilated pupils) –> vomiting

Question 10

Describe the mechanisms of action of anti-emetics including ADRs

Answer 10

D2 antagonist e.g. Domperidone acts on postrema on floor of 4th ventricle
Used in acute nausea/vomiting
ADR - prolactin release
5-HT antagonist e.g. Ondansteron inhibits vagal stimulation
Used in high dose radiation sickness, given with corticosteroid
ADRs - headaches, constipation, flushing

Question 11

Understand the effects of laxatives on the GIT and their ADRs

Answer 11

Bulk forming e.g. Isphagula, Fybogel - distend gut, stimulate motility
Vegetable fibre - enzyme resistant
Faecal softeners e.g. Arachis oil, Glycerol
Osmotic e.g. Lactulose, Mg, Na salts - cause water retention in small bowel –> peristalsis
Macrogels - powder form
Irritant/Stimulative e.g. Castor Oil, Senna, Phenylmathane - excitation of sensory nerve endings –> water and electrolyte retention –> peristalsis

Question 12

Understand the effects of antidiarrhoeals on the GIT and their ADRs

Answer 12

Loperamide (Imodium), Codeine - decrease motility, increase anal tone
Bulk forming e.g. Isphaghula
Fluid adsorbents e.g. Kaolin
Bile acid sequestrants

Question 13

Recognise the main features of IBS

Answer 13

Bouts of stomach cramps, bloating, diarrhoea, constipation, flatulence

Question 14

List the defensive and aggressive factors affecting the integrity of the gastric mucosa

Answer 14

Defensive - epithelial integrity, cell replication, mucous membrane, vascular supply
Attack - acid (pH 1/2), H. pylori, drugs e.g. NSAIDs