Pancreatic exocrine secretions and its control Flashcards
What forms the ductal tree and what does it empty into?
Acini form sacs → connect to the ductal tree → empty into the duodenum
Give a range of cells that are found within the exocrine ducts of the pancreas
- Microvilli
- Intercalated ducts- squamous epithelium
- Intralobular ducts-cuboidal or low columnar epithelium
- Interlobular ducts – columnar epithelium/goblet cells
- Pancreatic duct, which enters the duodenum at the common bile duct
What cells and ducts amalgamate to form the pancreatic duct?
Look and describe the pancreas under a microscope
Acini → microvilli→ intercalated duct → intralobular duct → interlobular duct →Pancreatic duct
How much fluid does the pancreas secrete a day?
Secretes 1.5L of fluid/day
What does the pancreas secrete?
What do the acinar cells secrete?
What are these enzymes secreted as?
Where are they activated?
- Sodium and HCO3–rich juice, albumin, globulin and digestive enzymes
- Acinar cells secrete digestive enzymes to breakdown carbohydrates, fats, proteins, and nucleic acids
- Enzymes secreted in inactive form (as zymogens) to prevent autodigestion
- Activation of enzymes occurs in the duodenum
Whar anions and cations does the pancreas secrete?
The anions that are secreted in the pancreatic juice:
HCO3-, Cl-, SO42-, HPO42-
The cations that are secreted in the pancreatic juice:
Na+, K+, Ca2+, Mg2+
Describe how the composition of pancreatic juice changes as it passes through the ducts
Composition of the juice is modified 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)
• ….more CO2 and HCO3- produced in the blood
• ….CO2 diffuses in and forms H2CO3 with H2O
Thus, [HCO3-]pancreatic juice and its rate of production proportional [HCO3-]blood
What happens to the concentrations of chloride ions and hydrogen carbonate ions after Secretin is secreted?
Cl- decreases and HCO3- increases - reciprocal effect
The reduced amylase and Cl- concentrations upon secretin infusion may be a dilution effect as the volume of pancreatic juice is increased
What are the 3 major enzymes secreted from the pancreas?
- Proteolytic enzymes (trypsin, chymotrypsin and carboxypeptidase)
- Amylase
- Lipase
Also
Ribonuclease
Deoxyribonuclease
Look at the table of enzymes, activators and substrates
On image
Digestive enzymes survive different lengths of time in the small intestine
What is the percentage of enzymes that reach the small intestine?
- Amylase: 75%
- Trypsin: 20%
- Lipase: 1%
Where does Chymotrypsinogen and amylase travel to 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 controls the release of pancreatic secretions?
- Neuroendocrine signals
- Vagal (parasympathetic) stimulation: enhances rate of secretion of enzymes and aqueous components of pancreatic juice
- Sympathetic stimulation: inhibits secretion (decreased blood flow?)
- Secretin and CCK: stimulate secretion of pancreatic fluid (enzyme- and bicarbonate-rich secretions)
What does release of Secretin from mucosa of duodenal and jejunum induce?
- Induces pancreatic duct cells to secrete HCO3- -rich pancreatic juice, but ↓ enzyme content
- Secretin also stimulates production of bile by the liver
Describe the release of CCK from duodenal and jejunum in response to fatty acids (amino acids, and peptides)
• CCK stimulates pancreatic acinar cells to synthesise and release enzyme-rich pancreatic juice; and stimulates the secretion of concentrated bile from gallbladder for fat absorption
CCK contracts the gallbladder and relaxes the sphincter of Oddi → release of bile into duodenum
Note that NO and VIP also relax the sphincter of Oddi to release secretions from the pancreas and gallbladder (pancreatic juice)
• CCK potentiates the effects of secretin, which is a weak agonist of acinar cells
