Phys: Pancreas Flashcards
What are the most plentiful cells in the pancreas?
Acinar cells (84%).
J: This refers to the condition in which the major and accessory pancreatic ducts do not fuse.
What is pancreas divisum?
What are ways in which the endocrine pancreas influences the exocrine?
Venous blood from the islets perfuse neighboring acini before entering the portal vein, exposing them to hormones:
(1) insulin stimulates enzyme synthesis and secretion
(2) somatostatin and glucagon inhibit enzyme secretion
What is the major stimulus for water and bicarbonate secretion by pancreatic duct epithelial cells?
Secretin.
What is the MoA of secretin?
It activates adenylate cyclase in pancreatic duct cells, which opens apical chloride channels (CFTR). Bicarbonate is exchanged for luminal chloride.
What disease impairs the secretion of water and bicarbonate by pancreatic duct cells?
Cystic fibrosis.
What are the functions of secretin?
(1) Retards gastric emptying
(2) Promote mesenteric blood flow
(3) Stimulates secretion of bicarbonate from the pancreas
What stimulates secretin release?
Presence of acid in the intestine.
How does the storage and release of amylases, lipases and proteases differ?
Amylases and lipases are stored and secreted in their active form, whereas proteases are kept as inactive proenzymes.
How is trypsin activated?
The trypsinogen released by the pancreas is activated to trypsin by enterokinases on the intestinal brush border.
What is PSTI?
Also called SPINK1, it is a peptide inhibitor of trypsin in the cytoplasm of pancreatic acinar cells.
Where is most amylase produced?
Pancreas (though salivary glands do as well).
What does amylase do?
It cleaves 1,4-glycoside linkages.
What are the products of amylase digestion?
(1) maltose
(2) maltotriose
(3) limits dextrin containing 1,6-linkages
What are causes of maldigestion?
(1) excess gastric acid
(2) inadequate enzyme or bicarbonate excretion
(3) poor bile flow
(4) intestinal dysmotility
What are causes of malabsorption?
Mucosal disease.
Can a change in diet affect the proportions of enzymes synthesized by the pancreas?
Yes.
What hormones increase the free cytoplasmic calcium in pancreatic acinar cells?
(1) CCK
(2) ACh
(3) GRP
(4) substance P
What hormones increase cAMP in pancreatic acinar cells?
(1) VIP
(2) secretin
What is the major stimulus for the secretion of pancreatic enzymes?
Cholecystokinin (CCK).
What does CCK do?
(1) Contracts gallbladder
(2) Relaxes the hepatopancreatic sphincter of Oddi
(3) Delays gastric emptying
Where is CCK primarily produced?
Discrete upper intestinal cells (though also in CNS and peripheral nerves of the intestine).
What stimulates the release of CCK?
Presence of peptides, amino acids, fatty acids in intestine.
What are the stimulatory phases of pancreatic secretion?
(1) cephalic
(2) gastric
(3) intestinal
By what is the cephalic phase of pancreatic secretion mediated?
The vagus nerve.
J: This refers to the act of chewing and expectorating.
What is sham feeding?
J: This substance inhibits the cephalic phase of pancreatic secretion.
What is atropine?
What occurs in the gastric phase of pancreatic secretion?
Distention of the stomach sends a vagovagal response to the pancreas, triggering release of pancreatic enzymes.
What can inhibit the release of CCK?
(1) intraluminal trypsin that isn’t complexed to meal protein
(2) IV amino acids and glucose
J: The presence of this substance in the terminal ileum and colon can inhibit gastric emptying and pancreatic secretion.
What is oleic acid?
What are some tests for pancreatic function?
(1) 72 hr fecal fat
(2) Sudan stain of stool (for fat)
(3) analysis of duodenal secretion after meal, CCK, or secretin stimulation
(4) endoscopic ultrasound
(5) MRI
(6) CT
What percentage of lipase output must be lost in order to see a noticeable increase in fecal fat?
90%.
What are the functions of bile?
(1) Excretion of metabolites of lipid waste, like bilirubin
(2) Fat and fat-soluble vitamin absorption
(3) Excretion of cholesterol
(4) Secretion of IgA
What is a bile salt that increases canalicular flow? Decreases?
(1) ursodeoxycholic acid
(2) lithocholic acid
What is the rate-limiting step in the secretion of bile?
Secretion into the canaliculus, as its against a concentration gradient.
How is the intracellular bile salt concentration controlled?
A nuclear receptor, farnesoid X factor (FXR), senses intracellular bile salt. Its stimulation suppresses bile salt synthesis and increases canalicular secretion.
What is the rate-limiting step in bile salt synthesis?
Cholesterol synthesis from acetate by HMGCoA reductase.
What is the difference between primary and secondary bile salts?
Primary bile salts are synthesized in the liver, whereas secondary salts are later manipulated by bacteria in the colon.
What is the purpose of the conjugation of bile salts?
It makes stronger acids which ionizes the upper small intestine, preventing back diffusion into bile ducts. Also, ileal receptors only bind conjugated bile salts.
What does it mean for a bile salt to be conjugated?
Its carboxyl side chain is conjugated with taurine or glycine.
What is the role of lecithin in micelles?
It increases the ability to solubilize cholesterol.
What value is equal to the amount of bile synthesized by the liver?
The amount of fecal bile.
What are 3 causes of bacterial overgrowth in the small bowel?
(1) motility disorders
(2) surgical blind loops
(3) small bowel diverticuli
Why is bacterial overgrowth in the small bowel a concern?
It causes premature deconjugation of bile salts leading to precipitation of bile acids and inadequate micelle formation.
What is a possible role of cholesterol and phospholipids in a mixed micelle?
To protect the GI mucosa from the toxic effects of the bile salts.
