Physiology 3120 Lecture Notes - Lecture 5: Cystic Fibrosis, Tandem Pore Domain Potassium Channel, Pancreatic Lipase Family
9 May 2018
School
Department
Course
Professor
Physiology 3120
Dr. Woods
GI Tract
Lecture 5
The Pancreas
- Both exocrine and endocrine function
o review endocrine secretions (insulin, glucagon and somatostatin)
- Exocrine secretions are secreted into the duodenum
- Acinar cells make the enzymatic secretions
o The enzymatic secretions are modified as they travel through the larger ducts of the
pancreas
o The larger ducts are surrounded by ductule cells
o The ductule cells secrete into the enzymatic solution made by the acinar cells
o They secrete things like water and bicarbonate to make the volume of the secretion
larger and to provide an alkaline environment for which the enzymes will enter into the
acidic duodenum
- Bicarbonate - from ductal cells
- Pancreatic Amylase
o Very similar to salivary amylase
o Digests starch (complex carbohydrates)
o Pancreatic amylase has a lot more time to interact with the starches in our diet bc its
acting within the duodenum and our small intestine can control how long the enzyme is
active (unlike the salivary amylase, which is inactivated by the acid in your stomach
when you swallow it)
- Other enzymes are secreted as zymogens – they are secreted as inactive proteins that must be
cut to become activated – all these are protein digesting enzymes once they have been
o Trypsinogen Trypsin
o Chymotrypsinogen Chymotrypsin
o Procarboxypeptidase —> Carboxypeptidase
o Proelastase —> Elastase
- Pancreatic Lipase
o Digests lipids
o Compared to the lingual lipase and gastric
lipase, pancreatic lipase is the most
important – it digests the most amount of fat
o This is bc it has help within the small
intestine
- Ribonuclease
o Breaks down RNA in our food
- Deoxyribonuclease
o Breaks down DNA in our food
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- When these pancreatic secretions come from the acinar cells, they travel down the ducts and
they enter into the small intestine
- The larger pancreatic duct joins and becomes part of the common bile duct
- The common bile duct, which is initially closed off by the sphincter of obii, when it is open,
secretions of the pancreas go into the small intestine
- When we have trypsinogen (one of the zymogens) come into the contact with enterocyte, we
have brush border enzymes
- One of the brush border enzymes on these absorptive cells is enterokinase
- Enterokinase is embedded in the microvilli of absorptive cells
- Enterokinase takes trypsinogen and cuts it into something smaller called trypsin (enzyme)
o So the activation of trypsinogen occurs bc of the action of enterokinase
- Trypsinogen goes on in a cascade fashion to digest all of the other zymogens produced by the
pancreas
o Ex: chymotrypsinogen is cut and formed into chymotrypsin due to the actions of trypsin
o Ex: procarboxypeptidase is converted into carboxypeptidase due to the actions of
trypsin
- The small intestine is a safe place bc all this is happening when food is also present in your small
intestine
o All these protein digesting enzymes are being activated in the presence of dietary
protein and not autodigesting the wall of the small intestine or going back and digesting
the pancreas
o So this is a specific event to prevent the pancreas from digesting itself
- Note: pancreatitis is a disease where you get inappropriate activation of trypsin within the ducts
of the pancreas this activation may occur within the acinar cells themselves where there are
proteases that may cleave trypsinogen into trypsin
o If this happens within the acinar cells or the ducts of the pancreas, we get activation of
all the other zymogens early on in the pancreas and the pancreas starts digesting itself
- There is also another coenzyme called procolipase which is also made by acinar cells and is
activated to colipase in this same cascade
o It’s a coenzyme for pancreatic lipase
Regulation of Pancreatic Secretions
- Acinar cell secretions from the pancreas are homogeneous
o The acinar cells make the same ratio of all those enzymes
o Every acinar cell will secrete packets of vesicles containing all of the zymogens
o So its not like the salivary glands which can have a mixed population (have some mucus
secreting cells, enzyme secreting cells) – these acinar cells all make the same thin g
- Ratio of zymogens and digestive enzymes will change with changing diets but each acini will still
secrete the same composition
o Ex: if you decide you are going to eat less animal protein, you start making less
proelastase (bc elastase is good at digesting animal proteins)
o So as you shift what you eat, the pancreas will shift which zymogens and enzymes it
makes
- Ductal cells modify secretions by adding bicarbonate and water
o We have the ability to trigger those ductal cells to secrete more bicarbonate and water if
necessary to the total secretion product that is coming from the pancreas
- Cholecystokinin will stimulate acinar secretions, Secretin will stimulate ductal secretions
o
Cystic Fibrosis and Pancreatic Insufficiency
- The pancreatic insufficiency that comes with CF is the reason why patients don’t survive
- Mutation in CF: mutation in the Cl- channel called CFTR
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Both exocrine and endocrine function: review endocrine secretions (insulin, glucagon and somatostatin) Exocrine secretions are secreted into the duodenum. Pancreatic lipase: this is bc it has help within the small intestine. Ribonuclease: breaks down rna in our food. Deoxyribonuclease: breaks down dna in our food. When these pancreatic secretions come from the acinar cells, they travel down the ducts and they enter into the small intestine. The larger pancreatic duct joins and becomes part of the common bile duct. The common bile duct, which is initially closed off by the sphincter of obii, when it is open, secretions of the pancreas go into the small intestine. When we have trypsinogen (one of the zymogens) come into the contact with enterocyte, we have brush border enzymes. One of the brush border enzymes on these absorptive cells is enterokinase. Enterokinase is embedded in the microvilli of absorptive cells.
