L21: The Exocrine Pancreas Flashcards
the pancreas consists of what 2 types of glandular tissue
- islets within parenchyma of glands (endocrine fxn)
- exocrine glands (digestive enzymes)
pancreatic juice is rich in _____ and ______ and is secreted into the lumen of acini and modified on its way through the ducts
digestive enzymes and bicarbonate
pancreatic fluids drain where
into SI
what are the functions of pancreatic juice
- neutralize acids from stomach when food enters duodenum pH changes dramatically
- provide enzymes for the digestion of food (amylases, lipases, proteases)
what enzymes break down glucose polymers
amylases
what enzymes digest triglycerides, phospholipids and cholesterols
lipases
what enzymes break down proteins into amino acids, di/tri and oligopeptides
proteases
what is ecbolic secretion
protein secretion by acinar cells
what cells secrete the aqeous portion of pancreatic juice (electrolytes, bicarbonate, water)
centroacinar and ductal cells
= hydroelatic secretion
hydroelatic secretion
alkaline and watery secretion by duct cells
what is pancreatic bicarbonte secretion into the SI necessary for
neutralization of gastric acid emptied into SI
Bicarbonate is released via a chloride bicarbonate exchanger that is driven by…
the gradient for bicarbonate
the composition of pancreatic juice depends on ?
rate of secretion (flow rate)
at low flow - Cl- is main anion
at high flow, HCO3 concentration increases
elevated levels of _____ stimulate flow rate of pancreatic juice, causing a change in the composition of the fluid
secretin
what things regulate pancreatic secretion
- CCK and gastrinstimulate acinar cells to secrete proenzymes
- Secretin stimulates duct cells to secrete water and bicarbonate
- vagal input stimulates acinar and duct cells
2 ____ and one _____ control mechanisms stimulate pancreatic secretion
hormonal
neural
vagal input (Ach) stimulates what cells
acinar and duct cells
CCK and gastrin stimulate what cells
acinar, to secrete proenzymes
secretin stimulates what cells
duct cells, to secrete water and bicarbonate
pancreatic secretion occurs in what 3 phases
- cephalic
- gastric
- intestinal
what is the most important phase of pancreatic secretion and why
intestinal phase; it controls 80% of pancreatic secretion
during the intestinal phase of pancreatic secretion, _____ is released from ___ cells in response to fats and amino acids in the duodenum
CCK, I-cells
CCK enters circulation and stimulates acinar cells
during the intestinal phase of pancreatic secretion, _____ is released from ____cells in response to peptides and AA in stomach
gastrin
during the intestinal phase of pancreatic secretion, in response to a low pH in the duodenum, ______ is released from ____ cells and stimulates duct cell secretion
secretin
S cells
peptide hormone synthesized and relased by entero-endocrine I cells
CCK
where are I cells present
dudoenum, jejunum, ileum
what are the stimulators for I-cells (CCK) ; what do I cells target
released when fatty acids and amino acids enter duodenum
target: acinar cells
what organs does CCK act on
- gallbladder –> contractions
- pancreas –> acinar secretion
- stomach –> reduced emptying
- sphincter of bile/pancreatic duct –> relaxation
peptide hormone synthesized & released by entero-endocrine ‘S cells’
secretin
where can S cells be found
duodenum
what is the stimulator for S cells and what do S cells target
low pH (<4.5) in the duodenum
target: Duct cells
what phases of pancreatic secretion share regulation by the vagal pathway
cephalic and gastric
pancreatitis occurs when…
digestive enzymes are activated upon release into the pancreatic duct system which causes autophagy and inflammation
an inflammation of the pancreas with histological presence of edema, neutrophilic infiltrate and necrosis
pancreatitis
what can cause pancreatitis
- obstruction causing impaired flow in pancreatic ducts - zymogen granules and proenzymes get trapped in ducts and prematurally activate
- spontaneous trypsinogen cleavage overwhelming the trypsin inhibitor causing premature activation of trypsin
why does pancreatitis cause malabsorption and maldigestion causing anorexia, lethargy, exercise intolerance/weakness, V/D+, abdominal pain, dehydration, fever, arrythmia (caused by electrolyte imbalance)
due to a lack of enzymatic activity
what is the key factor in initiating pancreatic inflammation
activation of trypsin within the acinar cells
pancreatic lipases ______ lipids (triglycerides) which are used for long term energy storage
hydrolyze
triglycerides are apolar and have to be converted into _____ in order to be transported
glycerol, monoglycerides, diglycerides, fatty acids
what cells produce pancratic lipases
pancreatic acinar cells
what proteins maintain the bicarbonate gradient
- Na HCO3 cotransporter
- intracellular carboanhydrase (CA)
- Na-K ATPase
- Na-H exchanger
- proton pump
- chloride channel + exchanger
digestive enzymes are activated and work best in an ______ environment
alkaline
what are the 4 types of pancreatic digestive enzymes
proteases
amylolytic enzyme
lipases
nucleases
where are digestive enzymes activated
in the intestinal lumen of the duodenum
what enzyme converts inactive trypsinogen into active trypsin which is then able to activate other proenzymes
enterokinase
what is the function of protease inhibitors in the zymogen granule
blocks the action of prematurely activated enzymes
what is the function of nondigestive proteases
they degrade active enzymes
