Gastric Secretion Flashcards
What is the role of the fundus, body, antrum of the stomach
Fundus (top part) = storage
Body (main part) = storage, secretion (mucus, HCl, Pepsinogen, intrinsic factor)
Antrum (bottom part) = mixing/grinding, gastrin secretion
What is intrinsic factor used for
Absorption of B12
What cells release gastrin
G-cells
How is HCl produced
Hydrogen + chloride in stomach lumen creates osmotic gradient —> water coming into stomach lumen
Which hormones increase activity of the hydrogen potassium pump, therefore increasing HCl production (3)
Gastrin
Histamine
Acetylcholine (parasympathetic nervous system)
What inhibits the hydrogen potassium pump
Prostaglandins
What is the cephalic phase of gastric acid secretion
Cephalic = in head (before any food has made it to the gut)
Vagus nerve innervates the G cells producing gastrin —> HCl production
Why is the cephalic mechanism important for gut health
Before swallowing stomach produces acid in advance which is a protective preemptive mechanism for things entering stomach
How does distension of stomach (arrival of food), peptides (protein) in lumen and gastrin/Ach stimulate parietal cells to produce HCl
Distension of stomach (by food) = vagal/enteric reflexes —> ACh acting on parietal cells
Peptides in lumen = G cells —> gastrin acting on parietal cells
Gastrin/ACh = ECL cells —> histamine acting on parietal cells
How does the cephalic phase inhibit gastric acid secretion
Stopping eating —> decreased vagal activity
How does the gastric phase inhibit gastric acid secretion
Decreasing stomach pH (due to increased HCl) —> decreased gastrin (negative feedback system)
How does the intestinal phase inhibit gastric acid secretion (which reflex is this and what is released)
(Intestinal phase = stomach starts to empty its contents)
Acid from stomach enters duodenum triggering splanchnic reflex + release of secretin
Both cause reduction in gastrin secretion and reduce stimulation of parietal cells in gastrin
How does fat/CHO in duodenum inhibit gastric acid secretion
Releases gastric inhibitory peptide (GIP)
Causes reduction in gastrin secretion + reduction in parietal HCl secretion
What are enterogastrones
Hormones released from gland cells in duodenal mucosa
(Secretin, cholecystokinin, GIP) that inhibit the forward motion (analward) of chyme
What stimulates enterogastrones release (4)
Acid
hypertonic solutions
fatty acids
monoglycerides in duodenum
What do enterogastrones do
Prevent further acid build up in duodenum:
- inhibit gastric acid secretion
- reduce gastric emptying (inhibit motility/contract pyloric sphincter)
Why is stomach acid build up in duodenum bad
Damaging to pancreatic enzymes and duodenum itself
What is pepsinogen
Active precursor of pepsin
Why is pepsin stored as pepsinogen
Prevents pepsin from digesting the cells containing it
In what pH conditions is pepsinogen turned into active pepsin
Acidic solution (pH < 3)
Only operates in very low pH environments
What is the role of gastric mucus
Cytoprotective (protects the cells)
- mechanical injury: makes surface slippery so abrasive materials glide off surface
- protection against corrosion (gastric acid - mucus has VERY high bicarbonate concentration) and digestion (pepsin)
What is the role of intrinsic factor (produced by what cells, what does it do, once in complex where is it absorbed)
Produced: parietal cells
Required for vitamin B12 absorption
The intrinsic factors/B12 complex absorbed from ileum
What condition arrises from intrinsic factor defect
Pernicious anaemia
What does somatostatin do
Reduce gastric secretions by limiting release of gastrointestinal hormones (including secretin and gastrin)
Reduces gut motility
