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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