Pancreatic Exocrine Secretions & Its Control Flashcards
What do acinar cells secrete?
Acinar cells secrete digestive enzymes
What do acini form, connect to and empty into?
Acini form sacs/lobule → connect to the ductal tree → empty into duodenum
What cells are intercalated ducts made up of?
squamous/cuboidal epithelial cells
What cells are intralobular ducts made up of?
cuboidal or low columnar epithelial cells
What cells are extralobular ducts made up of?
columnar epithelial cells
What cells are interlobular ducts made up of?
columnar epithelial/goblet cells
How many litres of fluid is secreted per day by the pancreas and what does it contain?
Secretes 1.5L of fluid/day (containing, e.g. sodium and HCO3–rich juice,
albumin, globulin and digestive enzymes)
What do acinar cells secrete and what does it breakdown?
Acinar cells secrete digestive enzymes which breakdown carbohydrates,
fats, proteins, and nucleic acids
What form are enzymes secreted in and what does it prevent?
Enzymes secreted in inactive form (as zymogens) to prevent auto-digestion
(of pancreas)
Where does activation of enzymes secreted from pancreas occur?
Activation of the enzymes occurs in the duodenum
What are the anions secreted in the pancreatic juice?
HCO3-, Cl-, SO42-, HPO42-
What are the cations secreted in the pancreatic juice?
Na+, K+, Ca2+, Mg2+
What does the HCO3- rich juice from the pancreas help to neutralise?
HCO3–rich juice from the pancreas (and gallbladder)
help to neutralise gastric acid (↑pH to 6 or 7)
What modifications occur to the pancreatic juice as it travels through the duct?
- Epithelial cells actively exchange Cl-/HCO3-
- H+ is actively eliminated by Na+/H+ exchanger
- H+ exchanged for K+ - driven by Na+/K+ ATPase
- H+ neutralises HCO3- (H2CO3 formed)
- …… CO2 and HCO3- produced in the blood
- ……. CO2 diffuses in and forms H2CO3 with H2O
What are the 3 major types of enzymes secreted from the pancreas?
-Proteolytic enzymes
-Amylase
-Lipase
What do proteolytic enzymes digest and what does this put the pancreas at risk at?
Digestion of proteins; so the pancreas is at risk of autodigestion
Where are enterokinase enzymes found?
In the brush border of duodenum
What is enterokinase secreted in response to?
Secreted in response to CCK
What does enterokinase do?
Converts trypsinogen to trypsin
What are enterokinase inhibitors of?
Inhibitors of autodigestion
What does trypsin activate in acute pancreatitis and what does this cause the formation of and from what substrate?
Trypsin activates phospholipase A2 (PLA2) in the
pancreatic duct
Lecithin–>Isolecithin
What does isolecithin so to pancreatic tissue?
disruption of pancreatic tissue, membrane damage &
necrosis
what is a good diagnostic test for acute pancreatitis?
↑ [pancreatic α-amylase]blood
What enzymes cross the basolateral membrane and what does this suggest?
- Chymotrypsinogen and amylase cross the basolateral membrane of
pancreas
Suggests bidirectional permeability of the basolateral membrane to
digestive enzymes
What type of signalling controls secretions of the pancreas?
Neuroendocrine signals
What does vagal stimulation do to secretions of the pancreas?
enhances rate of secretion of
enzymes and aqueous components of pancreatic juice
What does sympathetic stimulation of the pancreas do?
inhibits secretion
What does secretin and CCK stimulate secretion of in pancreas?
stimulate secretion of pancreatic fluid
What is the control of pancreatic secretions in the cephalic phase and what is stimulated and released?
vagal (ACh and VIP) stimulation of gastrin release from antrum → some enzyme-rich pancreatic juice
What is the control of pancreatic secretions in the gastric phase and what is secreted and released?
Distension (vago-vagal reflex on fundus or antrum), amino
acid- and peptide- (in antrum)-stimulated gastrin secretion → release of
enzyme-rich pancreatic juice
What does the vago-vagal reflex release in the gastric phase?
Vago-vagal reflex also causes ACh release
What does a vagotomy reduce the response to?
Vagotomy → 50%↓ in response to acidic chyme
What is the control of pancreatic secretions during the intestinal phase and what is secreted and released?
secretin and CCK; enteropancreatic reflexes - Acidic chyme
in duodenum and jejunum induces the secretion of pancreatic juice (HCO3
- and enzymes)
What does secretin from duodenal and jejunum induce?
Induces pancreatic duct cells to secrete HCO3- -rich pancreatic juice, but
↓ enzyme content
-Secretin also stimulates production of bile
What does CCK stimulate from the duodenal and jejunum?
CCK stimulates pancreatic acinar cells to synthesise and release enzyme-
rich pancreatic juice; and stimulates the secretion of concentrated bile
for fat absorption
What does CCK do the gallbladder and what does this release?
CCK contracts the gallbladder and relaxes the sphincter of Oddi →
release of bile and some HCO3- into duodenum
What does CCK potentiate and why?
CCK potentiates the effects of secretin, which is a weak agonist of acinar
cells
