Gastric Secretion Flashcards
What is function of the fundus of the stomach?
Storage
What is the function of the body of the stomach?
Storage
Production of:
Mucus, HCl, Pepsinogen, Intrinsic Factor
What is the function of the antrum of the stomach?
Mixing and grinding
Production of gastrin
How is the antrum equipped for grinding of food?
Thicker/more powerful muscularis
How is gastrin produced?
G-cells
What is the function of mucus in the stomach?
Prevent autodigestion of the stomach by HCl
What is the cellular composition of gastric glands?
Mucus neck cells
Chief Cells
Parietal cells
What do neck cells produce?
Precursors to surface mucous cells
Where is pepsinogen produced?
Chief cells
What do parietal cells produce?
HCl
Intrinsic factor
How is H2CO3 produced in the parietal cells of the stomach?
CO2 pulled from blood
Combined with water and Carbionic Anhydrase to form H2CO3
What is the fate of H2CO3?
Very unstable
Dissociates to:
HCO3
H
What is the fate of dissociated protons?
Active loading from the parietal cell into the lumen via proton pumps
How do Proton pumps work?
One H exchanged for 1 K using H-K ATPase
What is the fate of dissociated carbonate?
Pumped out of the parietal cells into the blood in exchange for Cl
What is the effect of the Cl entering the cell from the blood?
Cl passively flows from the parietal cell into the lumen, creating an osmotic gradient which water follows into the lumen
What is the source of CO2 for the production of protons?
Metabolic waste
How does Gastrin effect protein pumps?
Gastrin -> Ca release -> Stimulation of protein kinase -> increased protein pump activity
How does acetylcholine effect protein pumps?
Gastrin -> Ca release -> Stimulation of protein kinase -> increased protein pump activity
How does Histamine effect protein pumps?
Gs coupled reactor converts ATP –> cAMP which triggers protein kinase and increases PP activity
How do prostaglandins effect protein pumps?
Activate G-inhibitory proteins and stop the conversion of ATP –> cAMP, reducing protein kinase activity .’. reducing PP activity
Which gastric acid secretion mechanism is neurocrine?
Vagus/local reflexes
Which gastric acid secretion mechanism is endocrine?
gastrin
Which gastric acid secretion mechanism is paracrine?
Histamine
What is the cephalic phase of Gastric acid secretion?
Seeing/smelling/tasting food causing vagal stimulation
How does vagus stimulation effect gastric acid secretion?
Increased ACh
Stimulation of G-cells: increase of gastrin
What is the effect of Gastrin and ACh on ECL cells?
Triggers histamine release
How does the distension of the stomach stimulate gastric acid production?
Distension of the stomach stimulates Vagal/Enteric reflexes - triggering ACh release
How do peptides in the lumen stimulate gastric acid production?
Stimulation of G-cells to release gastrin
How do gastrin and ACh stimulate gastric acid production?
Stimulation of ECL cells which release Histamine
How does stopping eating effect gastric acid secretion?
Inhibition due to reduced vagal activity
What is the effect of pH falling on gastric acid secretion?
Inhibitory - Gastrin secretion is reduced
Acid in the duodenum triggers what?
Enterogastric reflex
Secretin release
The Enterogastric reflex and Secretin release trigger what?
Decreased Gastrin secretion
Decreased gastrin effect on parietal cells
Fat or CHO in duodenum trigger what?
GIP release
GIP triggers what?
Reduced gastrin secretion
Reduced parietal HCl secretion
What are enterogastrones?
Hormones released from gland cells in duodenal mucosa
Secretin
CCK
GIP
When are enterogastrones released?
Response to acid, hypertonic sltn, FAs or CHOs in the duodenum
What is the role of enterogastrones?
Prevent further acid build up in the duodenum
How do enterogastrones slow acid build up?
Inhibit gastric abit
Contract pyloric sphincter (slow emptying)
Pepsinogen is converted into pepsin when?
pH < 3
Presense of other pepsin
How is pepsin neutralised?
Neutral pH
What is the role of pepsin?
Cleaves peptide bonds (endopeptidase)
