GI:Acid secretion

Question 1

What are functions of the GI tract?

Answer 1

• Digestion
• Absorption
• Excretion
• Hollow organs
• Supporting organs (Liver, gall bladder and pancreas)

Question 2

How is the GI tract controlled?

Answer 2

1. Neuronal
   * Myenteric plexus
   * Meissners Plexus
   * Parasympathetic
   * Sympathetic (ACh)

2.Hormonal
* Gastrin
* Histamine (Prostoglandins E2 & I2 inhib acid secre)

Question 3

What are Oxyntic glands?

Answer 3

• Enterochromaffin-like cell walls (ECL) and chief cells and parietal cells that have a unique folds that face lumen whcih secretes acid

Question 4

What are the cells of the Stomach?

Answer 4

1. Goblet cells - Mucus (protects stomach lining)
2. Parietal cells - Gastric acid (HCL)
3. Chief cells - Pepsinogen (protease precursor)
4. D cells - Somatostatin
5. G cells - Gastrin (stim acid secr)

Question 5

What do parietal cells respond to?

Answer 5

• Gastrin
• Histamine
• Acetylcholine
• Prostoglandins (E2, I2) are inhibitory

Question 6

What are Parietal cells?

Answer 6

• Unique folds with protein pumps to secrete acid, and the other side is bicarbonate excretion to produce safety barrier
• Connected to blood supply

Question 7

What is the H/K/ATPase proton pump?

Answer 7

• H ions gen in cell
• Actively pumped out in exchange for K
• Bicarb ions transported out of basolateral and maintain mucus layer
• Cl+K maintain movt of ions

Question 8

What stimulates acid secretion?

Answer 8

1. Gastrin:
   * Peptide hormone
   * Stimulate acid secretion from parietal cells
2. ACh
   * Released from neurons and stimulated muscarinic receptors
3. Histamine:
   * Paracrine (local ECL cells)

Question 9

What is the ‘one-cell’ hypothesis?

Answer 9

• (Direct pathway) - ACh, Gastrin, Histamine involved
• Stimulate the parietal cell directly, triggering secretion of H+ into lumen

Question 10

What is the ‘two-cell’ hypothesis?

Answer 10

• (Indirect)
• ACh and Gastrin also stimulate ECL cell, resulting in secretion of histamine.
• The histamine then acts of parietal cell.

Question 11

What causes Dyspepsia? (Gastric acid secretion)

Answer 11

• Peptic ulceration, (heliobacter pylori infection–long term anti-inf)
• Gastro-oesohpageal reflux disease - Bile secretion into stomach
• Zollinger Ellison syndrome (gastrin sec tumour)
• Gastritis - Spicy food, alcohol etc

Question 12

What are ulcers and common sites of them?

Answer 12

• Can lead to erosion of mucous lining
• Damage protective layers
• Leads to excessive bleeding
• Esophageal ulcer (Cardiac sphincter)
• Gastic ulcer
• Duodenal ulcer (Pyoloric sphincter)

Question 13

What are treatments for Dyspepsia?

Answer 13

• Antibiotics for erradication
• Symptom relief:
  1. Antacids and Alginates
  2. Proton pump inhib
  3. H2 receptor antagonists

Question 14

How do Proton pump inhibitors work and what are the side effects?

Answer 14

Mechanism
* Inhibit gastic H+, K+, ATPase enzyme system

Side effects
* Headaches
* Abdominal pain
* Diarrhoea
* Nausea/Vomiting
* Constipation
* Osteoporosis

E.g.
* Omeprazole
* Lanosprazole

Question 15

How do H2 receptor antagonists work and what are the side effects?

Answer 15

Mechanism
* Block action of histamine at H2 receptors of parietal cells

Side effects
* Headache
* Anxiety
* Depression
* Cardio effects

E.g.
* Ranitidine, Cimetidine

Question 16

How do Antacids work and what are the side effects?

Answer 16

Mechanism
* Inc gastric pH > 4 and inhibits action of pepsin
* Osmotic retention of fluid

Side effects
* N+V
* Hypophophatemia
* Chalky taste
* All the normal
* Electrolyte imbalance

E.g.
* Magnesium hydroxide

Question 17

How do K competitive acid blockers work and what are the side effects?

Answer 17

Mechanism
* Inhib H/K/ATPase in gastric parietal cells at final stage of acid secretary pathway

Side effects
* Naopharyngitis
* Falls
* Confusion
* Upper respiratory tract infection
* Eczma
* Normal

E.g.
* Vanoprazan

Question 18

How do Cytoprotective agents work and what are the side effects?

Answer 18

Mechanism
* Stim mucous production and enhance blood flow throughout lining of GI tract

Side effects
* Normal: Diarrhoea, Abdominal pain, Headache, Constipation

E.g.
* Misoprostol sucralfate

Question 19

What do NSAIDs do in the gut?

Answer 19

• Oral NSAIDs are causes of peptic ulceration and/or damage
• Most common adverse drug reaction
• NSAIDs inhib cyclo-oxygenase
  1. COX1-Gastric protection
  2. COX2-Role in inf
• NSAIDs given in combo with Misoprostol
  1. PGE1 analogue binds to prostanoid receptors to block gastric H+ secretion

Question 20

What is the triple therapy method?

Answer 20

• 2 antibiotics and/or PPI or H2 antagonist
• For H-pylori eradication (Peptic ulceration)