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52 Cards in this Set
- Front
- Back
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What is the structure of the pancreas like?
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Compound - consisting of 2 parts
-Acinus -Pancreatic duct |
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What is secreted by the
-Acinus -Pancreatic duct |
Acinus: pancreatic enzymes
Duct/ductules: Sodium bicarb |
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How do the combined pancreatic enzymes and sodium bicarb enter the small intestine?
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They flow together through the pancreatic duct, join the hepatic duct, empty into the duodenum via the papilla of Vater
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What surrounds the papilla of Vater?
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The sphincter of Oddi
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What stimulates pancreatic secretion?
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Presence of chyme in the duodenum
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What determines the content of pancreatic juices?
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The food that is in the duodenal chyme at the time ;)
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What types of enzymes are in pancreatic secretions?
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Enzymes for digesting all three major food types in diet:
-Protein -Carb -Fats |
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What are the most important protein-digesting enzymes in pancreatic juice?
Which is most abundant? |
-Trypsin (most abundant)
-Chymotrypsin -Carboxypolypeptidase |
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What sets carboxypolypeptidase apart from the other two protein enzymes?
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Its the only one that can break down proteins all the way to the amino acid state.
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Which pancreatic enzyme digests carbs?
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Pancreatic amylase
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What is the starch that can't be hydrolyzed by amylase?
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Cellulose
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3 main enzymes for fat digestion in pancreatic juice:
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1. Pancreatic lipase
2. Cholesterol esterase 3. Phospholipase |
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How are the protein digestive enzymes secreted?
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As inactive precursors
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When do protein enzymes become active?
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Only when they get into the small intestine through the ampulla of vater
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What activates Trypsinogen?
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The enzyme enterokinase or by itself
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What activates Chymotrypsinogen?
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Trypsin
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What keeps Trypsin from being activated before getting to the duodenum?
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Trypsin Inhibitor
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What happens if trypsin inhibitor is not working?
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Trypsin would digest the pancreatic duct and Acute Pancreatitis would ensue
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What structural part of the pancreas secretes enzymes?
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Acinus
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What else can cause Acute Pancreatis, other than just inhibiting Trypsin inhibitor?
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Duct blockage
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What are the 3 important constituents of pancreatic secretions? Where is each from?
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1. Enzymes -> Acini
2. Water 3. Bicarbonate 2/3 are from ducts/ductules epithelial cells |
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What does the bicarb concentration reach when pancreas enzyme secretion is stimulated copiously?
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145 mEq/L
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How does that bicarb concentration compare to that in plasma?
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It is 5X higher
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Why does the pancreas add bicarbonate to its secretion?
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To neutralize the acidity of the chyme entering the duodenum from stomach.
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Steps in Sodium bicarb secretion by pancreatic ductules:
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1. CO2 diffuses from blood into ductule epithelial cell
2. CA converts CO2+H2O into H2CO3; splits into H+ / HCO3- 3. HCO3- diffuses into lumen as H+ exchanges via active transport for sodium; sodium diffuses out to form Sodium Bicarbonate in ductule lumen! |
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Why is sodium secreted along with bicarbonate?
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To provide electroneutrality
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What results from the overall movement of sodium and bicarb into the duct lumen of pancreas?
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Osmotic pressure gradient so water comes along with it.
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What do we call the resulting sodium bicarb solution in the ductule lumen?
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Isosmotic
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What are the 3 stimulating factors for pancreatic secretion?
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1. ACh from PNS vagus nerves and other cholinergic nerves in ENS
2. CCK 3. Secretin |
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Where is CCK secreted from and in response to what?
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From dupdenal and upper jejunal mucosa; when food enters the small intestine
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Where is Secretin secreted, and in response to what?
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Same as CCK; duodenum and upper jejunum; except this is in response to highly acid food in small intestine.
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ACh and CCK STIMULATE WHAT PART OF PANCREATIC SECRETION?
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THE ACINI - Increased ENZYMES but not water and ions
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What usually happens to the enzymes secreted in response to ACh and CCK stimulation?
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They get stored in Acini and ductules until more water is stimulated to be secreted and wash them out.
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What is stimulated by Secretin?
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Release of more water and ions, not pancreatic enzymes - opposite to ACh/CCK stimulation.
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How do the stimulatory factors for pancreatic secretion relate?
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MULTIPLICATIVE - together they elicit MUCH HIGHER pancreatic secretion than if added together.
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Three phases of pancreatic secretion:
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1. Cephalic
2. Gastric 3. Intestinal |
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What happens during the cephalic and gastric phases of pancreatic secretion?
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20% of pancreatic secretions; stimulated by ACh release from vagal nerve endings -> mostly enzymes, little H2O/electrolytes
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What happens to the enzymes stimulated for secretion during the gastric/cephalic phases?
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Mostly just stay in the pancreatic acinus b/c need more water to wash them out.
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What happens to pancreatic secretions during the intestinal phase?
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Copious amts of bicarb and water are stimulated for secretion by the hormone Secretin.
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Why is so much bicarb released during the intestinal phase?
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To neutralize the stomach acid in chyme entering the duodenum.
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Where is Secretin made / released? What is its initial structure like?
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Made in S-cells of the duodenal and jejunal mucosa; starts out inactive as Prosecretin
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What stimulates release and activation of Prosecretin?
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Acid chyme with pH less than 4.5-5 entering duodenum
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How does Secretin get from the jejunal / duodenal cells to the pancreas?
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Via the bloodstream
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Changing what factor changes the amt of secretin released?
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pH in chyme -> due to hydrochloric acid
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What is the result of the intestinal phase of pancreatic secretion?
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A neutral solution of chyme with NaCl and water is created; CO2 goes to the lungs via the bloodstream for expiration
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Why is it important that Secretin cause neutralization of duodenal chyme?
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Because pancreatic enzymes require a slightly alkaline or neutral medium in order to be active.
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pH of resulting duodenal chyme:
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8
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Where is cholecystokinin made?
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In I cells in the duodenal and jejunal mucosa
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What stimulates release of CCK?
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Presence of food in upper small intestine --> proteoses, peptones, and longchain FAs
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Effect of CCK on pancreatic secretions:
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Secretion of ENZYMES
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How does the effect of CCK compare to that of ACh?
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Same nature but more pronounced
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how much pancreatic secretion is stimulated by CCK after a meal?
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80%
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