GI:Acid secretion Flashcards
What are functions of the GI tract?
- Digestion
- Absorption
- Excretion
- Hollow organs
- Supporting organs (Liver, gall bladder and pancreas)
How is the GI tract controlled?
-
Neuronal
* Myenteric plexus
* Meissners Plexus
* Parasympathetic
* Sympathetic (ACh)
2.Hormonal
* Gastrin
* Histamine (Prostoglandins E2 & I2 inhib acid secre)
What are Oxyntic glands?
- Enterochromaffin-like cell walls (ECL) and chief cells and parietal cells that have a unique folds that face lumen whcih secretes acid
What are the cells of the Stomach?
- Goblet cells - Mucus (protects stomach lining)
- Parietal cells - Gastric acid (HCL)
- Chief cells - Pepsinogen (protease precursor)
- D cells - Somatostatin
- G cells - Gastrin (stim acid secr)
What do parietal cells respond to?
- Gastrin
- Histamine
- Acetylcholine
- Prostoglandins (E2, I2) are inhibitory
What are Parietal cells?
- Unique folds with protein pumps to secrete acid, and the other side is bicarbonate excretion to produce safety barrier
- Connected to blood supply
What is the H/K/ATPase proton pump?
- 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
What stimulates acid secretion?
- Gastrin:
* Peptide hormone
* Stimulate acid secretion from parietal cells - ACh
* Released from neurons and stimulated muscarinic receptors - Histamine:
* Paracrine (local ECL cells)
What is the ‘one-cell’ hypothesis?
- (Direct pathway) - ACh, Gastrin, Histamine involved
- Stimulate the parietal cell directly, triggering secretion of H+ into lumen
What is the ‘two-cell’ hypothesis?
- (Indirect)
- ACh and Gastrin also stimulate ECL cell, resulting in secretion of histamine.
- The histamine then acts of parietal cell.
What causes Dyspepsia? (Gastric acid secretion)
- 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
What are ulcers and common sites of them?
- Can lead to erosion of mucous lining
- Damage protective layers
- Leads to excessive bleeding
- Esophageal ulcer (Cardiac sphincter)
- Gastic ulcer
- Duodenal ulcer (Pyoloric sphincter)
What are treatments for Dyspepsia?
- Antibiotics for erradication
- Symptom relief:
1. Antacids and Alginates
2. Proton pump inhib
3. H2 receptor antagonists
How do Proton pump inhibitors work and what are the side effects?
Mechanism
* Inhibit gastic H+, K+, ATPase enzyme system
Side effects
* Headaches
* Abdominal pain
* Diarrhoea
* Nausea/Vomiting
* Constipation
* Osteoporosis
E.g.
* Omeprazole
* Lanosprazole
How do H2 receptor antagonists work and what are the side effects?
Mechanism
* Block action of histamine at H2 receptors of parietal cells
Side effects
* Headache
* Anxiety
* Depression
* Cardio effects
E.g.
* Ranitidine, Cimetidine
