Secretion in the Pancreas and Small Intestine Flashcards
(43 cards)
What is the overall function of the pancreas?
Important in digestion of nutrients, fat, proteins with huge reserve capacity resection (95%)
Providing the appropriate environment for enzymatic digestion in the small bowel
important in regulating the fed and fasted states (insulin and glucagon)
What does the pancreas bicarb rich fluid do?
The bicarb rich fluid is used by the pancreas to neutralise stomach acid (exocrine function)
How is the pancreas connected to the small intestine?
Via a series of ducts such as the intra/interlobular ducts and then the main ducts
What is the Ampulla of Vater?
The point at which the pancreatic duct merges with the common bile duct
(contents of gall bladder, liver and pancreas all go via the main pancreatic duct into the small intestine
What is the function of the pancreatic acinar cells?
are specialized/polarised for the production and export of large quantities of zymogens
Secretes isotonic NaCl rich fluid to hydrate the dense protein rich material
What is the function of the goblet cells?
Goblet cells produce mucus important for 1. Lubrication 2. Hydration, 3. Mechanical protection of surface epithelial cells. 4. Immunologic role -binding of pathogens and interacting with immune-competent cells ultimately preventing pancreatic infections
What is the function of the centroacinar cells?
are the very first cells of the intercalated duct and thus are located at the junction of the pancreatic acinar cells and duct cells, function questioned
What are the triggers for the protein secretion from the pancreatic acinar cell?
Ach and CCk both ultimately activate PKC and release of calcium leading to zymogen release.
VIP and secretin activate adenyl cyclase leading to cAMP production and PKA activation.
What is the function of the pancreatic duct cell
Secrete HCO3- rich fluid which hydrates and alkinizes the protein rich secretions of the acinar cell. (neutralise the acid)
How does the pancreatic duct cell carry of the chloride bicarbonate exchange?
- cl- and HCO3 exchanger brings Cl- into the pancreatic duct cell and HCO3- enters the duct lumen
- CFTR allows the diffusion of Cl- ions to leave the duct cell and return back to the duct lumen (chloride recycling)
- This process is triggered by ACh and secretin as they stimulate the PKC pathway.
What are S cells?
Found in the small bowel and secrete secretin when they recognise the acidic chyme to neutralise it.
What happens when CFTR is lost?
You wont get chloride recycling and therefore be unable to neutralise the acidic chyme from the stomach. You would also be unable to hydrate the thick proteinous fluid secreted by the acinar cells.
This would lead to thickening protein secretion and could lead to ductal obstruction or even pancreatic cell death (cystic fibrosis)
composition and function of pancreatic secretion
product of acinar, duct and goblet cells results in secretion of a pancreatic juice which is protein-rich embedded within an alkaline fluid.
the pancreas exhibits the highest rates of protein synthesis and secretion
Product is over 20 proteins which are mostly zymogens (inactive proproteins) which get activated when needed.
Why is the rate of pancreatic secretion dependent on being in the fed/fasted state?
Tightly interlinked with biliary/gastric secretions
Fasted state - post absorptive so low level release of pancreatic enzymes
Fed state - increased secretion
How are pancreatic secretions inhibited?
Somatostatin produced by D cells in the islets of Langerhans.
Inhibit the release of CCK and secretin as well as glucagon and insulin
What are the different phases of pancreatic secretion?
Cephalic phase
Gastric phase
Intestinal phase
What is the cephalic phase of pancreatic secretion?
Sight, taste, and smell of food. • Accounts for 25% Mediated by the stimulation of Ach receptors on the acinar cell and to a lesser extent duct cells. No involvement of CCK or secretin.
What is the gastric phase of pancreatic secretion?
Accounts for 10-20%
- release of hormones (gastrin) stimulated by amino acids in the G cells of the antrum. This signals through the CCk receptor on acinar cells
- stimulation of neural pathways, gastric distention stimulates low levels of pancreatic secretion through a vagovagal gastropancreatic reflex
What is the intestinal phase of pancreatic secretion?
Accounts for 50-80%
chyme entering the proximal small intestine stimulates a pancreatic secretion by 3 main mechanisms:
1. Gastric acid stimulates duodenal S cells to release secretin, which stimulates duct cells to secrete HC03 and fluid. 2. Lipids (monoglycerides/FFA) predominantly stimulate duodenal I cells to release CCK, which stimulates acinar cells to release digestive enzymes. 3. Lipids also activate a vagovagal enteropancreatic reflex that predominantly stimulates acinar cells.
Pattern of pancreatic enzymatic secretion is going to depend on the relative composition of the chyme (eg. High carb vs fats!)
How does the pancreas prevent autodigestion?
By preventing enzyme activity in the pancreas as the enzymes are produced in the inactive form initially.
Eg. Trypsinogen (inactive zymogen) when converted to trypsin will activate all the other zymogen enzymes.. Therefore we only want trypsinogen to become activate in the small intestine.
How is trypsinogen activate in the small intestine?
Enterokinase on the boarder of the small intestine cleaves trypsinogen into trypsin which activates the rest of the zymogen enzymes
What is SPINK1?
A pancreatic trypsin inhibitor
How is autodigestion prevented?
- Zymogens produced in inactive form
- secretory vesicles are impermeable preventing automatic release
- enzyme inhibitors (SPINK1)
- Low pH and ionic conditions in secretory pathway limiting enzyme activity.
what are the causes of acute pancreatitis?
GET SMASHED
Gallstones, Ethanol, Trauma
Steroids, Mumps, Autoimmune, Scorpion sting, Hypercalcaemia, ERCP, Drugs
