GI secretions: gastric, pancreatic and drugs for peptic ulcer disease Flashcards
What are the gastric secretory products?
HCl; intrinsic factor; pepsinogen; gastrin; mucus
What, where and stimulus of HCl secretion?
pareital cells;
body/fundus of stomach;
=>gastrin; ACh (from vagus); histamine
What, where and stimulus of intrinsic factor secretion?
pareital cells;
body/fundus of stomach;
=>gastrin; ACh (from vagus); histamine
What, where and stimulus of pepsinogen secretion?
chief cells;
body/fundus of stomach;
=> ACh (from vagus); gastrin; HCl
What, where and stimulus of gastrin secretion?
G cells;
Antrum;
=> small peptides/amino acids; vagus (via GRP); stomach distension
What, where and stimulus of mucus secretion?
mucous cells;
entire stomach;
ACh (from vagina)
inhibitors of HCl and intrinsic factor?
- Low pH inhibits (by inhibiting gastrin)
- prostaglandins
- chyme in duodenum (via GIP and secretin)
inhibitors of pepsinogen
H+ (via somatostatin)
inhibitors of gastrin
H+ (via somatostatin)
action of mucus
forms gel on mucosa to protect mucosa from HCl and pepsin;
traps HCO3 to helps neutralize acid
action of gastrin
- increase HCl secretion (parietal cells)
- increase pepsinogen secretion (chief cells)
- increase histamine secretion by ECL cells
action of pepsinogen
- Digests up to 20% of proteins
- converted to pepsin w/ low pH and pepsin (autocatalytic)
action of intrinsic factor
- necessary for VITAMIN B12 absorption by ileum;
- forms complex w/ vitamin B12
action of HCl
- kills pathogens
- activates pepsinogen to pepsin
What are the 3 primary triggers of H+ secretion?
- ACh (from vagus) => M3 muscarinic receptor
- Histamine => H2 histamine receptor
- Gastrin => unidentified receptor
Describe the 3 steps in gastric H+ secretion
1) parietal cell=> CO2, H2O converted to H+ and HCO3 via carbonic anhydrase
2) H+ secreted into lumen of stomach by H-K ATPase => Cl- is secreted w/ H+
3) HCO3 absorbed into bloodstream in exchange for Cl-
What is alkaline tide?
after meal=> enough H+ secreated to raise pH of systemic blood and turn urine alkaline => alkaline tide
3 phases of gastric secretion
cephalic, gastric, intestinal phases
how does cephalic phase of gastric secretion occur?
“senses” increase gastric secretion via PANS => 30% responsible for H+ secretion
how does gastric phase of gastric secretion occur?
-food in stomach increases secretion;
-proteins, peptides, alcohol, caffeine cause *gastrin release
-gastric distention initiates vagovagal reflexes
=>60% of acid secretion
how does intestinal phase of gastric secretion occur?
-protein digestion products in duodenum stimulate gastrin secretion;
-absorbed amino acids act to stimulate H+ by parietal cells
=>less than 10% of acid secretion due to meal
What are the drug classes for peptic ulcer disease?
antacids;
H2 antagonists; PPI;
mucosal protective agents; antibiotics
primary antacid agents
MgOH; AlOH; CaOH
What are the effects of antacids?
Mg=> laxative effect
AlOH=> constipating effect
Agents of H2 antagonists?
*cimetidine;
ranitidine; famotidine; nizatidine
How does cimetidine work and what type of physio effects are associated?
inhibits hepatic drug metabolizing enzymes
antiandrogen effects
Agents of PPI
*omeprazole
lansoprazole; esomeprazole; pantoprazole; rabeprazole
How do PPI work?
irreversibly inactivate H-K ATPase => block H+ secretion
What disease do PPI work well in?
PUD, ZE syndrome; GERD
mucosal protective agents
- Sucralfate
- misoprostol
action of sucralfate
polymerizes in stomach and forms protective coating over ulcer beds
when is misoprostol used?
PGE1 derivative used for peptic ulcers caused by NSAIDs
What and why are the antibiotics used in peptic ulcer disease?
macrolides; metronidazole; tetracyclines
=> treat H. pylori
What are the exocrine secretions of pancreas caused by?
acinar cells and ductal cells
How do acinar cells produce exocrine secretions?
contain numerous enzyme-containing granules in cytoplasm
how do ductal cells produce exocrine secretions?
secrete HCO3
How do exocrine secretions reach duodenum?
pancreatic duct
What is the fxn of HCO3 in duodenum?
- neutralizes HCl in chyme entering stoamch
- deactivates pepsin
What causes an increase in HCO3 production?
H+ entering duodenum
*=> S cells secrete secretin
=> secretin acts on pancreatic ductal cells to increase HCO3 production
What enzyme is responsible for HCO3 production? and where does this occur?
ductal cells contain *carbonic anhydrase
How does HCO3 get into the blood?
exchange for Cl-
If a person goes and eats a lot of Gus’s fried chicken, what is responsible for this digestion?
*CCK released by I cells in response to meals w/ small peptides, amino acids and fatty acids
=> stimulate pancreatic enzyme secretion
What is the role of ACh in pancreatic enzymes?
via vagovagal reflexes=> stimulates enzyme secretion; potentiates action of secretin
What provides protection of pancreatic acinar cells against self-digestion?
- proteolytic enzymes are secreted as inactive precursors
* produce enzyme inhibitors
What is the role of enzyme inhibitor production wrt protection of acinar cells?
inactivate trace amounts of active enzyme formed w/in
What is the role of proteolytic enzymes being secreted as inactive precursors for acinar cell protection?
these enzymes get activated in gut lumen
What are pancreatic enzymes that are not pro-enzymes so acinar cells are not protected?
ribonucleases; amylase; lipase
What are the proteases of pancreas and associated reaction catalyzed?
trypsin=> proteins to peptides;
chymotrypsin=> proteins to peptides;
carboxypeptidase => peptides to amino acids
What are the polysacchardases of pancreas and associated reaction catalyzed?
amylase => starch/glycogen to maltose, maltotriose, alpha-limit dextrins
What are the lipases of pancreas and associated reaction catalyzed?
- phospholipases A & B=> phospholipids to phosphoate, FA, glycerol
- esterases=> cholesterol esters to free cholesterol and FA
- TAG lipases=> Triglycerides to FA and monoglycerides
What are the nucleases of pancreas and associated reaction catalyzed?
- ribonuclease=> RNA to ribonucleotides
* deoxyribonuclease=> DNA to doxyribonucleotides
