Gastric Secretion Flashcards
What are the 3 parts of the stomach?
Fundus
Body
Antrum
What is the function of the fundus?
Storage
What is the function of the body of the stomach?
Storage
Mucus, HCl, Pepsinogen and intrinsic factor production
What is the function of the antrum of the stomach?
Mixing/ Grinding
Gastrin production
What does mucous neck cells secrete?
Mucus
What does chief cells secrete?
Pepsinogens - inactive precursor of pepsin
What does parietal cells secrete?
HCl and Intrinsic factor
What are the 3 main gastric glands?
Mucous neck cells
Chief cells
Parietal cells
Explain how HCl is produced and released out apical membrane into stomach lumen
CO2 from blood crosses basolateral membrane of cell - joins with water and carbonic anhydrase to make carbonic acid
This dissociates into H and bicarbonate
H uses HKATPase pump
H and Cl join with water to make HCl
What happens to bicarbonate when dissociated from carbonic acid?
Exchanges with Cl across basolateral membrane and leaves into blood to increase pH
What can stimulate the HKATPase pump ?
Gastrin (hormone) binding on basolateral membrane to release Ca - protein kinase C
Histamine binds to release Gs then AC to convert ATP to cAMP which releases protein kinase A
ACh binds to muscarinic receptor releasing Ca - protein kinase C
What can inhibit the HKATPase pump?
Prostaglandins
What 3 mechanisms control gastric acid secretion?
Neurocrine - vagus/ local reflexes
Endocrine - gastrin
Paracrine - histamine
Explain the cephalic phase - stimulating gastric acid secretion
Sight, smell and taste of food causes vagus nerve to release ACh and G cells to release gastrin - works on parietal cells
Gastrin/ACh works on ECL cells releasing histamine - parietal cells
What during the gastric phase stimulates gastric acid secretion?
Distention of stomach
Peptides in lumen
Gastrin/ ACh
How does distention of stomach stimulate gastric acid secretion?
Triggers vagal/ enteric reflexes releasing ACh which stimulates parietal cells
How does peptides in stomach stimulate gastric acid secretion?
Triggers G cells which release gastrin - stimulates parietal cells
How does gastrin/ ACh stimulate gastric acid secretion?
Triggers ECL cells to release histamine which stimulates parietal cells
What in the cephalic phase inhibits secretion of gastric acid?
Stopping eating decreases vagal activity
What in the gastric phase inhibits gastric acid secretion?
Decreased pH from increased HCl production then decreases gastrin
What in the intestinal phase inhibits gastric acid secretion?
Acid in the duodenum
Fat/ CHO in the duodenum
How does acid in the duodenum stop gastric acid secretion?
Enterogastric reflex and secretin release
These decrease gastric secretion and gastrin stimulation of parietal cells
How does fat and CHO in the duodenum stop gastric acid secretion?
Causes GIP release which decreases gastrin secretion and parietal HCl secretion
What are enterogastrones?
Hormones released from gland cells in the duodenal mucosa - secretin, CCK and GIP
Why are enterogastrones released?
In response to acid , hypertonic solutions, fatty acids or monoglycerides in duodenum
What is the function of enterogastrones?
Act collectively to prevent further acid build up in the duodenum
What are the 2 strategies that enterogastrones use to prevent build up of acid in duodenum?
Inhibit gastric acid secretion
Reduce gastric emptying so inhibit motility/ contract pyloric sphincter
When is pepsin active?
In low pH <3
What does zymogen storage prevent?
Zymogen is inactive precursor and prevents cellular digestion
When is pepsins inactivated?
Neutral pH
Where is gastric mucus produced?
By surface epithelial cells and mucus neck cells
Explain the cytoprotective role of gastric mucus
Protects mucosal surface from mechanical injury
Neutral pH from bicarbonate protects against gastric acid corrosion and pepsin digestion
What is required for vitamin B12 absorption?
Intrinsic factor
What is the only non-compensated/ essential function of the stomach?
Production of intrinsic factor
Where is intrinsic factor/B12 complex absorbed?
From ileum
What is the defect if low production of intrinsic factor?
Pernicious anaemia - failure of erythrocyte maturation
