Glossary of 3 - Intestinal and pancreatic enzymes

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Intestinal epithelia, like the skin, is regenerated from subsurface layers of cells.
False: intestinal epithelia is renewed from a population of stem cells found at the bottom of the crypts.
An intestinal epithelial cell can have varying functions through its lifespan.
This is true: as cells migrate from the bottom of the crypts to the top of the villi they assume different functions at different levels.
What is the average lifespan of intestinal epithelial cells?
3 days
What is the function of Paneth cells? Where are they found?
The have an antibacterial function through the secretion of lysozyme and a-defensins. They are found at the bottom of the crypts.
What are the five epithelial lineages in the small intestine?
1.Paneth cells: <1%
2.Columnar cells: 90%
3.Enteroendocrine cells: ~1%
4.Goblet cells: 6-10%
5.M cells: <1%
What percentage of the mass of the pancreas is made up of exocrine cells?
Describe the polarity of pancreatic epithelia.
There are secretory mechanisms on the apical surface and hormone receptors on the basolateral surface.
Describe the process of enzyme secretion in pancreatic cells.
1.ACh and CCK bind receptors and stimulate the conversion of PIP2 to IP3
2.IP3 increases [Ca++] in the cell
3.Ca++ stimulates the fusion of secretory granules with the apical membrane
How does intracellular Ca++ cause water to accumulate in the pancreatic acini?
Ca++ stimulates Cl- channels on the apical membrane causing movement of Cl- into the lumen. This creates an electrical gradient that draws Na+ through paracellular channels into the lumen. The presence of NaCl creates an osmotic gradient that draws water.
What is the function of pancreatic amylase?
It breaks starches into di- and trisaccharides.
What is the function of pancreatic lipase?
It breaks up lipids, cholesterol esters, and triglycerides.
Enterokinase catalyzes the conversion of trypsinogen to trypsin. What two reactions are catalyzed by trypsin?
1.procarboxypeptidase to carboxypeptidase
2.chymotrypsinogen to chymotrypsin
How is HCO3- moved from centroacinar cells into the lumen? What powers this transport mechanism? Somatostatin and secretin are known to play roles.
Secretin upregulates cAMP which activates Cl- channels in the apical membrane. Cl- moves into the lumen and powers a HCO3-/Cl- antiporter as it returns. Somatostatin inhibits this process by downregulating cAMP.
Describe the role of H+ in centroacinar cells.
It is generated when carbonic anhydrase catalyzes the reaction of water and CO2 to form H+ and HCO3-. It is transported across the basolateral membrane by H+/Na+ antiporters.
Centroacinar cells secrete HCO3- into the lumen - how is water provided to make this into a buffer solution?
The presence of HCO3- and Cl- in the lumen creates an elctrical gradient that draws Na+ through paracellular channels. This in turn creates an osmotic gradient that draws water.
Vagus nerve endings release ACh near the pancreas during the cephalic phase. What effects does this have?
*weak stimulation for release of pancreatic enzymes
*contraction of the gall bladder
*relaxation of the sphincter of Oddi
During the gastric phase, gastrin weakly stimulates CCK receptors in the pancreas - what effects does this have? What increases these effects in the early intestinal phase?
*secretion of pancreatic enzymes
*contraction of the gall bladder
*binding of CCK to CCK receptors greatly intensifies these effects and strongly relaxes the sphincter of Oddi
In the late intestinal phase the pH in the duodenum is quite low, stimulating the release of a hormone. What is this hormone and what are its effects on the pancreas?
Secretin is released and stimulates the pancreas to release a solution of electrolytes and water to buffer the lumen.
As the pancreas secretes an alkaline solution of electrolytes and water, H+ is released into the blood stream. Why doesn't the blood then become acidic?
It is neutralized by the alkaline tide generated by the parietal cells as they secrete acid during the gastric phase.
How is HCO3- produced inside of centroacinar cells of the pancreas?
The cells contain carbonic anhydrase which catalyzes the production of H+ and HCO3- from water and CO2.

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