Lecture 21: The Exocrine Pancreas Flashcards
What are two types of pancreatic glandular tissue
- Endocrine (ex: islets)
- Exocrine (digestive enzymes)
Pancreatic juice is rich in ___ enzymes and ___
Digestive, bicarbonate
Pancreatic fluids drain into __
Small intestine
Obstruction or inflammation of the pancreatic duct causes ___
Pancreatitis
What is the function of the pancreatic juice
Neutralize acid from stomach
Describe the pH changes from stomach to duodenum
Stomach: 1.5-2
Duodenum: 5-7 (due to pancreatic juices)
How does the ion transport in pancreatic duct cells differ from that of gastric cells
Gastric cells producing HCl into stomach and HCO3- into blood resulting in alkaline tide
Pancreatic duct cells secreting HCO3- into lumen and H+ into interstitium
What is the function of amylase
Break down glucose polymers
What is the function of lipases
Digest triglycerides, phospholipids, and cholesterols
What is the function of proteases
Break down proteins to AA, di, tri and oligopeptides
___ cells secrete enzymatic components
Acinar cells
What is ecbolic secretion
Refers to protein secretion by Acinar cells
___ and ___ cells secrete electrolytes, bicarbonate and water
Centroacinar and ductal cells
What is hydroelatic secretion
Alkaline and watery secretion from duct cells
__cells modify the pancreatic juice
Ductal cells
Ductal cells modify pancreatic juice by removing __ and adding __ to render it more alkaline
Remove Cl- and add bicarbonate
Pancreatic secretion of bicarbonate into small intestine is essential for ___
Neutralizing gastric acid emptied into small intestine
How is bicarbonate secreted in the pancreatic juice
Via Cl/HCO3- exchanger
T or F: water follows bicarbonate in the secretion of pancreatic juice
True
*unlike salivary glands that have tight junctions impermeable to water
Composition of pancreatic juice depends on what
Rate of secretion/flow rate
At low flow rates __is the main anion ion in pancreatic juice
Cl-
At high flow rates __ concentration in pancreatic juice increases
Bicarbonate
Elevated levels of ___ stimulate secretory rate
Secretin
___ and ___ stimulate Acinar cells to secrete pro enzymes
CCK and gastrin
___ stimulates ductal cells to secrete water and bicarbonate
Secretin
___input stimulates both Acinar and ductal cells
Vagal
Describe the steps in stimulation of Acinar cells to production of pro enzymes
- Small peptides, FA act on I cells
- I cells release CCK
- CCK and ACH (PNS/vagal) stimulation increases intracellular Ca2+
- Phosphorylation of structural and regulatory proteins
Describe the steps in stimulation of ductal cells to secrete bicarbonate
- H+ ions act on S cells
- S cells secrete secretin
- Secretin drives chloride out of cell and ACh (PNS/vagal) drives HCO3- out and Cl- in (Cl-/HCO3- exchanger)
What are the two hormonal and one neural control to stimulate pancreatic secretion
Hormonal
1. CCK and gastrin stimulate Acinar cells
2. Secretin stimulates ductal cells
Neural
1. Vagal input stimulates Acinar and ductal cells
What % of pancreatic secretion does the intestinal phase control
80%
In response to __ and __ in the duodenum CCK is released from __ cells. CCK enters circulation and stimulates ___
Fat and amino acids, I cells, Acinar cells
In response to __ and __ in stomach gastrin in released from __ cells and stimulates ___
Peptides and AA, G cells, Acinar cells
ACh, CCK, and gastrin stimulate __ secretion
Enzyme
In response to low ___ in the duodenum secretin is released from __ cells. Secretin stimulates __ cell secretion
PH, S cells and ductal cells
What is the enteropancreatic reflex
Peptides and AA stimulating gastrin to act on Acinar cells and fats and amino acids stimulating CCK to act on Acinar cells- form digestive enzymes
Low pH stimulating secretin to secrete bicarbonate to neutralize acidic pH
Where are I cells found
Duodenum, jejunum and ileum
What stimulates I cells
Fatty acids and amino acids
What is the target for I cells
Acinar cells
What does CCK do to gallbladder
Contract
What does CCK do to pancreas
Acinar secretion
What does CCK do to stomach
Reduced gastric emptying
What does CCK do to sphincter on bile/pancreatic duct
Relaxes
CCK acting on gallbladder, pancreas, stomach and sphincter of bile/pancreatic duct ensures matching of ___
Ingesta delivery to digestive/absorptive capacity
Where do S cells exist
Duodenum
What stimulates S cells
Low pH <4.5
What is the target of S cells
Duct cells
Increasing levels of secretin ___secretory flow rate
Increases
Digestive enzymes are activated in the ___
Duodenum
Proenzyme, trypsinogen is cleaved by __
Enterokinase
Enterokinase cleaves trypinsogen to __ which then does what
Trypsin which then activates other pro enzymes
Why is proenzyme activation so complex in duodenum
Protective mechanism against autodigestion
What would be elevated on bloodwork that could indicate pancreatitis
Lipase levels
What is pancreatitis
Inflammation of the pancreas with histological presence of edema, neutrophilic infiltrate and necrosis
Describe the difference between normal function of pancreas and then what happens during pancreatitis
Normal: pancreatic enzymes activated once in duodenum
Pancreatitis: premature activation of enzymes in pancreatic duct resulting in autodigestion
What are two potential causes of pancreatitis
- Obstruction keep from pancreatic enzymes exiting pancreatic duct and they will eventually activate and autodigest
- Spontaneous trypsin cleavage
Pancreatitis causes __ and __ due to lack of enzymatic activity which can result in anorexia, lethargy, exercise intolerance/weakness, vomiting, diarrhea, abdominal pain, dehydration, fever, arrhythmia
Maldigestion and malabsorption
What is the key factor in intiating pancreatic inflammation
Activation of trypsin within Acinar cells
