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What makes the pancreas the main digestive organ
- Secretion of:
- Proteases
- Lipases
- Amylase
- HCO3
- 1.5L of secretions a day
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What path do pancreatic secretions follow to arrive in the duodenum
- Acinus
- Intralobular ducts
- Lubular ducts
- Main duct
- Common bile duct
- Duodenum
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What are the two stages of Pancreatic secretion
- Primary
- - Isotonic
- - NaCl (Acini)
- - Enzymes
- Ductal modification
- - HCO3 secreted
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Secretion of acinar fluid and the proteins that it contains is stimulated by
- Cholecystokinin (CCK)
- Acetylcholine
- Gastrin-releasing peptide
- (all act by mobilizing intracellular Ca++)
VIP and Secretin (act on cAMP)
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The hormone Secretin stimulates secretion of what in the pancreas
Water and electrolytes from the cells that line the extralobular ducts
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Where are the enzyme containing granules found on the acinar cells
Apical end
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Trypsinogen is activated to Trypsin by
Enterokinase found on the brush border cells of the intestines and in turn activates the rest of the enzymes released by the pancreas
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Enzymes secreted from acinar cells are in what form
Inactive
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I cells are found where and have what function
They are found on the epithelium of the intestines and they release CCK in to the blood stream
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I cells release Cholecystokinin (CCK) into the blood stream when triggered by
- CCK releasing peptide (paracrine messenger)
- Monitor peptide (from pancreas)
- Amino acids
- Fatty acids
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Presence of what inhibits the stimulation of I cells to release CCK into the blood stream
Trypsin
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What is the mechanism for keeping the pH of the intestines constant
- - low pH in Duodenu (below 4.5) causes S cells to release Secretin
- - Ductular cells (triggered by secretin) in the pancreas release bicarbonate
- - pH raises and inhibits further release from S cells
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In the un-stimulated state, the pancreatic flow is
- Low, and the electrolyte composition of
- pancreatic juice closely resembles that of blood plasma
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HCO3 release from the pancreas is done by what cells, under what direction
- Intralobular ducts
- Secretin & Acetylcholine
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What type of channel or pump is used in the Intralobular ducts and main ducts to excrete HCO3 into the lumen
HCO3/Cl- exchange
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The HCO3/Cl- exchange on the intralobular duct cells is dependent on
Secretion of CFTR protein and availability of Cl- in the lumen
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How does bicarbonate get into the interlobular cells of the pancreas
- Through a cotransport of Sodium and Bicarbonate on the basal end of the cell
- It is also made inside the cell via carbonic anhydrase
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How does carbon dioxide and water enter the cell for bicarbonate synthesis (carbonic anhydrase)
Passive diffusion across the membrane, no pump or channel are necessary
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What are the three phases of enzyme and bicarbonate secretion from the pancreas
- Cephalic
- Gastric
- Intestinal
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What triggers the cephalic phase in pancreatic secretion
- Sight, smell, and taste triggers the Vagus
- Vagus causes release enzymes directly
- Vagus causes indirect enzyme secretion through stimulation of gastrin releasing peptide which causes releases in gastrin, causing enzyme release
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How is the Gastric phase of pancreatic secretion triggered
- Distension of intestines
- Vago-vagal reflex
- Enzyme release
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In what three ways is the intestinal phase of pancreatic secretion triggered
- 1. H+ and fats trigger Secretin
- Secretin causes the release of Bicarbonate
- 2. Amino acids and fats cause CCK release
- CCK induces enzyme secretion
- 3. Vago-vagal response (distension of intestines)
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What is the comparative influence of pancreatic secretion between the 3 different stages
- Cephalic - 25%
- Gastric - 10-20%
- Intestinal - 50-80%
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What signals are most influential in increasing Secretin
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