Acid production and regulation Flashcards
4 main types of cells in stomach
Mucous cells, parietal cells (HCl and intrinsic factor), chief cells and enterendocrine cells (hormones, G cells secrete gastrin)
Approx __ litres of acid produced per day
2
Hydrogen pump is…
energy requiring, as H+ pumped against gradient
Gastric acid secretion mechanism
H2O + CO2 –> H2CO3), catalysed by carbonic anhydrase. Spontaneously dissociates into a H+ and HCO3–.
The H+ is transported into stomach lumen via the H+– K+ ATPase ion pump, uses ATP to exchange K+ with H+.
HCO3– transported out of cell into blood via a transporter protein called anion exchanger in exchange for Cl–. This chloride ion is then transported into the stomach lumen via a chloride channel.
This results in both hydrogen and chloride ions being present within the stomach lumen. Their opposing charges leads to them associating with each other to form hydrochloric acid (HCl).
Gastric phase (2) of regulating gastric acid secretion
Gastric distension, presence of peptides and amino acids
Gastrin released
Acts directly on parietal cells.
Triggers release of hormone histamine.
Acts directly on parietal cells.
Increased acid production.
Proteins as regulator of acid production
Effect of pH
Low luminal pH directly inhibits gastrin secretion, indirectly inhibits histamine release. Stimulates somatastatin (turns parietal cells off, inhibits acid production)
Duodenum in regulation
duodenal distension, senses chyme is hypertonic, low pH and presence of amino acids and fatty acids so triggers release of enterogastrones.
2 Enterogastrones
Secretin - inhibits gastrin release, promotes somatostatin release
Cholecystokinin (CKK)
Cephalic phase (1) of acid production regulation
Parasympathetic nervous system
sight, smell, taste and chewing
Acetylcholine release
ACh acts directly on parietal cells
ACh triggers release of gastrin and histamine
Increased acid production.
What are paracrine factors
Cells signal to each other, acts on neighbouring cells eg. histamine and somatostatin.
What is a peptic ulcer?
An ulcer is a breach in a mucosal surface. (epithelium stripped away due to gastric acid)
Caused by:
helicobacter pylori infection
Drugs (NSAIDS - ibuprofen, aspirin)
Chemical irritants (alcohol, bile salts)
Gastrinoma (tumour, too much acid made and not regulated)
How does gastric mucosa defend against attacks leading to ulcers?
Alkaline mucus,
tight junctions between epithelial cells,
replacement of damaged cells,
feedback loops to prevent too much acid being produced (negative feedback loop).
How does helicobacter pylori work
Lives in gastric mucus. Secretes urease, splitting urea into CO2 and ammonia.
Ammonia + H+ –> ammonium
Damages gastric epithelium along with proteases, phospholipases and toxin known as vacuolating cytotoxin A.
How do NSAIDs attack epithelium?
Non-steroidal anti-inflammatory drugs
Inhibit cyclo-oxygenase 1 which is needed for prostaglandin synthesis which stimulates mucus secretion.