Pancreas Flashcards
How many parts of the pancreas are there?
- Tail, body, neck, head, uncinate process
The majority of the pancreas is?
Exocrine acini (secreting digestive enzymes)
What do duct cells of the pancreas secrete?
Watery bicarbonate fluid
Describe the commonality of the various types of cells in the pancreas
- Insulin secreting B cells (70%)
- Glucagon secreting a cells (20%)
- Somatostatin secreting Delta cells (10%)
At what end of the duct are acinar cells located?
At the terminal end.
They secrete low volume, viscous enzymes
What is special about centroacinar cells?
They have the properties of acinar cells and duct cells
What are the functions of the duct cells?
Modify enzymes released by acinar cells (mobilise/neutralise acid chyme).
What connects Duct cells?
Tight junctions
Explain the mechanism of duct secretion
- HCO3- production through carbonic anhydrase. Na moves down gradient via paracellular junction. H20 follows.
- HCO3- secretion into duct. Cl/HCO3- exchanger. There is a Na/H+ pump at the basolateral membrane to bloodstream.
- Na management. Na gradient into cell managed by Na/K ATPase pump.
Contrast the blood leaving the stomach vs blood leaving pancreas
Stomach = alkaline
Pancreas blood = acidic
What enzyme converts trypsinogen into trypsin?
Enterokinase, which is a duodenal brush border enzyme.
What does trypsin do?
- Activates protease zymogens
- Converts prolipase to lipase.
- Autocatalyses trypsinogen to trypsin
What do proteases (e.g. carboxypeptidase, chymotrypsin) and trypsin do?
Convert longer peptides into shorter peptides
How do fats become fatty acids and monoglycerides?
Bile converts fats to triglycerides. Colipase and lipase convert triglycerides into fatty acids and monoglycerides.
What can pancreatic autodigestion cause?
Acute pancreatitis
Explain hormonal control of bicarbonate secretion.
Decrease in duodenal pH, stimulates secretin from S cells, secretin travels via blood to pancreas, binds to receptors on duct cells, cAMP 2nd messenger increases, Cl channels activated in apical membrane, Cl efflux, increased activity of anion exchanger, HCO3- efflux.
Explain how enzyme secretion from acinar cells is controlled.
- Hormonal. Fats/peptides in duodenum - triggers CCK release (I cells) - CCK travels in blood to pancreas - binds to CCK1 receptors on Acinar cells - PLC/IP3 2nd messenger - increased cytosolic Ca - Zymogen/inhibitor/enzyme granule exocytosed
- Neural. Vagus nerve releases ACh - binds to muscarinic receptors on Acinar cells - activation of PLC/IP3 2nd messenger, etc
What are the 3 phases of pancreatic secretion?
- Cephalic phase (vagus nerve)
- Gastric phase - distension of stomach (vagus nerve)
- Intestinal phase - acid/nutrient detection in duodenum. S cells and I cells.
Intestinal phase is mainly mediated by?
HORMONES. Negative feedback loop also present.
Majority of secretion is in which phase?
Intestinal phase
Acinar cells are activated in all 3 phases of pancreatic secretion. In the intestinal phase, another cell is also activated, which is?
Acinar cells and duct cells
CCK and secretin both are the most powerful increasers of HCO3- secretion.
T
CCK affects duct cells, but does secretin affect acinar cells?
NO
