DRS - pancreas Flashcards
Exocrine functions of the pancreas
To release zymogens which are inactive enzymes to allow digestion and absorption of nutrients
What is the ampulla of Vater?
Where the pancreatic duct merges with the common bile duct forming a swelling in the duodenal wall
What is the sphincter of Oddi?
Where the wall is thickened
The Oddi regulates and prevents reflux and controls flow of bile and pancreatic juices into the duodenum
What is the funciton of acinar cells?
Secrete zymogens, digestive enzymes and an isotonic fluid which hydrates the dense, protein-rich material that acinar cells secrete
How are acinar cells stimulated?
CCK (released from I cells) and ACh (binds to M3R) activates PKC pathway to release calcium
VIP and secretin activate PKA pathwat via adenylyl cyclase
What is the function of pancreatic duct cells?
secrete a HCO3- rich fluid to neutralise and hydrate the secretions from the acinar cells. It is also important for maintaining an optimal pH for enzymes, micelle formation and neutralising the intestine
How are pancreatic duct cells stimulated and how do they work?
The most powerful stimulus is secretin for HCO3- as it induces CFTR (a chloride channel) and Na-HCO3-
CFTR allows Cl- to diffuse from the cytoplasm into the lumen and then back into the cell via the Cl-HCO3- exchanger
How does secretin stimulate duct cells?
Secretin is produced from S cells and it stimulates HCO3- and fluid secretion in response to duodenal acidification
Activation of the secretin receptor activates a PKA pathway via adenylyl cyclase
This stimulates the apical CFTR cl- channel and the basolateral Na-HCO3- cotransporter
What does loss of CFTR expression cause?
In cystic fibrosis
Disrupts apical transport of duct cells and results in decreased secretion of HCO3-
Acinar cells make zymogens but thick secretions block thin ducts which can cause obstruction and damage pancreas
What inhibits pancreatic secretions?
Somatostatin made by D cells which inhibits CCK and secretin
What are the phases of pancreatic secretions?
- Cephalic phase - sight, taste, smell of food, mediated by ACh receptors
- Gastric phase - release of gastrin stimulated by peptides in the antrum, signals through CCK receptors on acinar cells
- Intestinal phase - chyme enters proximal small intestine stimulates pancreatic secretion
How does gastric distension stimulate pancreatic secretion?
Neural pathways - vagovagal enteropancreatic reflex
What are the 3 mechanisms by which chyme entering the small intestine stimulates pancreatic secretion?
- gastric acid stimulates S cells to release secretin which stimulates duct cells to secrete HCO3- and fluid
- lipids stimulate duodenal cells to release CCK which stimulates acinar cells to release digestive enzymes
- lipids activate vagovagal enteropancreatic reflex to stimulate acinar cells
How does the pancreas prevent autodigestion?
The pancreas produces inactive enzymes because if they were activated then they would start to digest the pancreas.
How are zymogens activated?
Zymogens flow through ducts to the lumen of the intestine. They can only be activated when they come in contact with enterokinase which is in the intestine. Enterokinase cleaves trypsinogen to trypsin and trypsin will cleave all the other zymogens.
