L06 - Secretions of the pancreas and intestines and control Flashcards
What is the overall function of the pancreas?
- Important in digestion of nutrients, fat, protein etc with huge reserve capacity resection (95%)
- Providing the appropriate enviro for enzymatic digestion in the SI
- Important in regulating the fed and fasted states (insulin, glucagon etc)
What is the ampulla of Vater formed from?
The major pancreatic duct merges with the common bile duct to form a swelling in the duodenal wall called the ampulla of Vater
- The muscular wall is thickened, forming the sphincter of Oddi
What is the function of the sphincter of Oddi?
- Regulate and prevent reflux
- Muscular valve that controls the flow of digestive juices (bile and pancreatic juice) through ducts from liver and pancreas into duodenum
- Regulate and prevent reflux
What is the function of acinar cells?
- Specialised/ polarised for the prod and export of large quantities of protein as predicted by cellular architecture
- RER, secretory granules, exocytosis at apical pole
What is the function of duct cells?
- Show a level of morphological heterogeneity along the ductal tree
- These are predominantly specialised for the transport of electrolytes
What is the function of centroacinar cells?
- The very first cells of the intercalated duct
- Thus are located at the junction of the pancreatic acinar cells and duct cells
- Function?
What is the function of goblet cells?
- Prod mucus which is important for:
- Lubrication
- Hydration
- Mechanical protection of surface epithelial cells
- Immunological role; binding of pathogens and interacting with immune-competent cells ultimately preventing pancreatic infections
Describe the exocrine pancreas structure
- Divided into lobules which drain into ductular networks (intralobular duct, interlobular ducts and then into a main duct)
- These ductular networks connect the entire gland to the lumen of the GIT
What is the acinus?
Represents a cluster of acinar cells that synthesise and secrete proteins into the lumen of the epithelial structure
What do pancreatic acinar cells secrete?
Plethora of zymogens (inactive enzyme precursors), digestive enzymes and an isotonic, plasma-like fluid that accompanies the secretory proteins
What is found within each pancreatic lobule?
Each lobule has a functional secretory unit of the gland
- Each secretory unit is composed of an acinus and a small intercalated duct
What is stimulation of the pancreas acinar cells mediated by?
Stimulation predom mediated through CCK-R and the muscarinic acetylcholine (ACh) receptors located on the basolateral cell memb
- These receptors signal through a common pathway - the phospholipase C signal transduction pathway, leading to increased enzyme secretion from the acinar cell
What are the two routes to activation for stimulation of protein secretion from the pancreatic acinar cell?
- ACh and CCK both ultimately activate PKC and release of calcium
- VIP and secretin both activate adenylyl cyclase, leading to the production of cAMP and the activation of PKA
What is the fluid secreted from acinar cells?
An isotonic, NaCl rich fluid which hydrates the dense, protein-rich material that the acinar cells secrete.
[Secretion of Cl- across the apical memb]
What stimulates the opening of the Cl- channels in the acinar cells?
The raised intracellular calcium which stimulates opening of apical membrane Cl- channels which ultimately stimulates NaCl secretion
- Same triggers as protein secretion (activation by neural/ humoral pathways such as muscarinic and CCK receptors)
