036 Drugs acting on the GI tract

Question 1

Which histamine receptor causes gastric acid secretion?

Answer 1

H2 (increases in cAMP)

Question 2

When does ulcer formation occur?

Answer 2

When gastric acid secretion > mucus secretion S

Question 3

How does H.pylori lead to formation of ulcers?

Answer 3

It is a gram negative bacteria that damages mucosal layer, allowing acid to pass through weakened mucos layer. It increases ammonia locally (neutralising acid and allowing it to survive).

Question 4

How would you treat H.pylori induced ulcer?

Answer 4

Proton pump inhibitors and amoxycillin or metranodizole

Question 5

How do NSAIDs produce ulcers?

Answer 5

NSAIDs inhibit prostaglandin E1 and E2. Prostaglandins are responsible for inhibiting HCl production by parietal cell and stimulating HCO3- release by mucous cells. By inhibiting prostaglandins, mucous cells are deactivated whilst parietal cells continue acid production, resulting in ulcers.

Question 6

What are some other causes of peptic ulcers other than H.pylori and NSAIDs?

Answer 6

Ischaemia, delayed gastric emptying,, gastric reflux, broken circadian rhythm (mucus production and bicarbonate release are not in sync).

Question 7

What are the 3 principal simulators of acid secretion?

Answer 7

ACh, Gastrin, Histamine

Question 8

Name some H2 antagonists

Answer 8

Cimetidine (reducing cAMP)
Ranitidine
Need to be given before sleeping because there is higher gastric acid secretion at 12am-3am.

Question 9

Why are proton pump inhibitors preferred to histamine inhibitors?

Answer 9

Proton pump inhibitors are stronger inhibitors than H2 antagonists and are longer lasting as they irreversibly bind to the H+/K+/ATPase pump.

Question 10

Name an example of a proton pump

Answer 10

omeprazole

Question 11

How do antacids work?

Answer 11

Neutralise gastric acid but not enough to reach ulcer healing. It is used to relieve pain from erosion and ulceration. MgOH2

Question 12

Name two mucosa protection drugs and their properties

Answer 12

Bismuth - barrier on epithelial cells and inhibits H.pylori

Sucralfate - complex with matrix, limiting proton diffusion

Question 13

3 types of diarrhoea

Answer 13

Secretion, osmotic, motility

Question 14

How do you treat diarrhoea?

Answer 14

Remove the cause, support fluid and electrolyte balance, give anti-diarrhoeal agents

Question 15

What are the 2 main types of antidiarrhoeal drugs?

Answer 15

Opiates e.g. codeine (anti-motility, antisecretory)
Muscarinic antagonists (many side effects)

Question 16

Treatment of constipation

Answer 16

Bulk and osmotic laxatives
Faecal softeners
Stimulate purgatives