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52 Cards in this Set

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