Gastric Secretion Flashcards
What is the function of the fundus?
storage
Functions of the body of the stomach?
Storage
Produce and Secrete - mucous, gastric acid, pepsinogen, intrinsic factor
Functions of the antrum of the stomach?
Mixing/ginding
Release gastrin
Describe the anatomy of a gastric gland
Gastric pit is up the way, comprised of surface mucous cells
Gastric gland is below, composed of mucous neck cells, parietal cells and chief cells
What do chief cells secrete? Parietal cells?
Chief cells secrete pepsinogens
Parietal cells secrete gastric acid and intrinsic factor
Describe production of HCL in parietal cells of stomach
H2O and CO2 combine to carbonic acid (H2CO3) via the enzyme carbonic anhydrase
H2CO3 almost immediately dissociates to HCO3 and H
HCO3 out across basolateral membrane, switched for Cl by transporter
Cl into lumen via leaky channels
H into lumen via H/K exchanger
H2O spontaneously follows H + Cl due to osmotic gradient, hydrochloric acid forms in lumen of stomach
Effect of gastrin on parietal cells?
interacts with receptors on basolateral membrane, causes influx of Ca into the cell
Ca activates protein kinases that increase H/K pump activity (HCL production)
Effect of histamine on parietal cells? What type of hormone is it?
Paracrine hormone - released locally
Interacts with G-coupled histamine receptors on basolateral membrane - causes cAMP release - protein kinases - increased H/K pump activity
Effect of acetylcholine on parietal cells?
ACh released by parasympathetic system, binds muscarinic receptors - influx of Ca into cells
Increases H/K pump activity via protein kinases
Effect of prostaglandins on parietal cells?
Exogenous prostaglandins inhibit gastric acid secretion
Stimulate mucous and bicarbonate secretion
3 Mechanisms of promoting gastric acid secretion?
Neurocrine - vagus/local reflexes
Paracrine - histamine (ECL cells)
Endocrine - gastrin (G cells)
Where is gastrin released from?
G cells in the antrum of the stomach, duodenum and pancreas
Where is histamine released from?
ECL cells in the gastric mucosa
enterochromaffin-like cells
What stimulates the release of ACh and gastrin?
The sight, smell or taste of food increases vagal output causing ACh/gastrin release
What stimulates ECL cells to release histamine?
Gastrin and ACh
What stimuli cause a reduction in gastric acid secretion?
Stopping eating - reduces vagal activity
Drop in pH of stomach lumen - reduces gastrin activity
Secretin being released from duodenum
How does the small intestine inhibit gastric acid secretion
Acid in duodenum stimulates enterogastric reflex and secretin release (secretin stimulates secretion by liver and pancreas)
Fat/carbs in duodenum causes decrease in gastrin and gastric acid secretion via GIP (hormone) release
What is the enterogastric (splanchnic) reflex?
Reflex in response to a pH of 3-4 in the duodenum, inhibits the release of gastrin by G cells - inhibits gastric secretion
What are enterogastrones?
Hormones released from glands in duodenal mucosa
Secretin, cholecystokinin (CCK) and GIP
Act to reduce acid buildup in duodenum by inhibiting gastric acid secretion and reducing gastric emptying
Where is CCK released from? What is its function?
Released in duodenum
Functions:
- Activate secretion of pancreatic enzymes
- Reduce gastric emptying
- Promote bile secretion
- Relax sphincter of Oddi
What is a zymogen? Example?
It’s an inactive precursor.
Pepsinogen
Where is pepsinogen secreted from and what catalyzes it’s conversion to pepsin?
It is secreted from chief cells of the stomach wall Low pH (<3) converts it to pepsin
What causes the inactivation of pepsins?
Raises in pH (towards normal ~7)
Which cells produce gastric mucus and what is its function?
Produced by surface mucus cells and neck mucus cells
Has a cytoprotective role - protects mucosal surface from mechanical injury. Keeps a neutral pH due to bicarbonate presence - protects against acid corrosion
What is the only essential (non-compensatable) function of the stomach?
Intrinsic factor production by parietal cells
Allows for vit B12 uptake, RBC maturation. If absent - pernicious anaemia
