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Lecture 65

Physiology 2130 Lecture Notes - Lecture 65: Common Bile Duct, Pancreatic Duct, Centroacinar Cell

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Anita Woods

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Lecture 065: Diseases of the GI Tract
The Pancreas
Have both exocrine and endocrine function
Exocrine secretion are secreted into the duodenum
Acinar cells
Ductal sectors
Make enzymatic secretion
Enzymatic secretion are modified as it travels down ducts
Ductal cells
Surrends larger ducts of the pancreas
Secretes into the enzymatic secretion made by the acinar cells
Secretes H2O and bicarbonate
Makes the volume of the secretion large
Makes the secretion alkaline to neutralize the acidic chyme in the
Exocrine secretion of the pancreas
Ductal cells
Pancreatic Amylase
Digest starch (complex carbohydrates)
Has a lot more time to interact with the starch (than salivary amylase)
Most important starch digesting enzyme
Inactive proteases (zymogens)
Trypsinogen -> Trypsin
Chymotrypsinogen -> Chymotrypsin
Procarboxypeptidase -> Carboxypeptidase
Proelastase -> Elastase
Pancreas makes pro-protease to prevent autodigestion
Pancreatic Lipase
Lipid digesting enzyme
Most important lipid digesting enzyme
Has help from the small intestine
Breaks down RNA and DNA
Common bile duct
Is closed by the sphincter of Oddi
Leads to the duodenum
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Activation of Pancreatic Zymogens
Trypsinogen is activated by enterokinase (brush-border enzyme)
Is cleaved it into trypsin when it comes into contact with an enterokinase
Trypsin in a cascade process, activates all the other zymogens and a coenzyme
Cleaves chymotrypsinogen, procarboxypeptidase, etc
Activation of protease in the small intestine is “safe” because it only occurs when there is
food in the small intestines
Protases will digest the dietary protein and not the wall of the GI tract
Protective to prevent autodigestion
Caused by inappropriate activation of trypsin within the ducts of the pancreas or
within the acinar cells
Causes the activation of all the other zymogens within the pancreas
Regulation of Pancreatic Secretion
Acinar cells secretion from the pancreas are homogenous
All make the same ratio of the same enzymes
Ratio of zymogens and digestive enzymes will change with changing diet but each acini
will still secrete the same composition
Bad for vegetarian to suddenly eat meat
Ductal cells
Modify acinar cell secretion
Adds bicarbonate and water
Hormone regulation
CCK (cholecystokinin)
Stimulate acinar secretion
Stimulate ductal secretion
Cystic fibrosis and pancreatic insufficiency
Lack of Cl- channel (CFTR) in the ductal cells
Modification to the secretion of the acinar cells are changed
Water and bicarbonate is secreted into the lumen of duct
Bicarbonate is secreted in exchange for the chloride (bicarbonate/Cl-
Cl- levels in the lumen is continuously maintained by the CFTR Cl- leak
How does mutations in the CFTR lead to pancreatic insufficiency
Lack of Cl- in the lumen leads to:
Less bicarbonate secreted
An increase in Cl- in the cell
Less water moving into the lumen by osmosis (following bicarbonate)
Results in:
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