Alimentary Systems 4 - Pancreas Flashcards
Briefly describe pancreatic development
- Develops as a foregut derivative, involving dorsal and ventral buds. Ventral is part of the hepatobiliary bud.
- Duodenum rotates to form a C shape - ventral bud swings round and both fuse
- Ventral bud becomes the main pancreatic duct
- Acini grow first then the fleshy islets
List the components of the pancreas moving outwards
- Head
- Uncinate (ventral bud)
- Neck
- Body
- Tail
How does pancreatic juice reach the duodenum?
Through the main and pancreatic ducts
Describe the location of the pancreas
On the posterior abdominal wall extending from the C shaped duodenum to the hilum of the spleen
List the relations of the pancreas
- Posterior relations include IVC, abdominal aorta and left kidney
- Close relations with the coeliac and superior mesenteric arteries
List the three endocrine secretions of the pancreas.
- Insulin promotes glucose transport, reduces blood glucose, and promotes protein synthesis
- Glucagon increases gluconeogenesis and glycogenolysis
- Somatostatin inhibits production of many hormones
What are the two functional parts of the pancreas?
- 2% endocrine, islets of Langerhans
- 98% exocrine secretes pancreatic juice into the duodenum
Describe the appearance of the acini
- Grape like clusters
- Secrete pro-enzymes into ducts
How are the islets composed?
- 15-20% a-cells which secrete glucagon
- 60-70% b-cells which secrete insulin
- 5-10% somatostatin
What are the two components of pancreatic juice?
- Low volume, viscous enzyme rich (produced by acinar cells)
- High volume, watery, HCO3-rich produced by duct and centroacinar cells
Why is bicarbonate secretion in the pancreas important?
- Produced by duct and centroacinar cells
- Neutralises chyme from the stomach raising pH and preventing damage
- Washes low volume enzyme secretion out of the pancreas
Describe the effect of duodenal pH on bicarbonate secretion rate
- pH < 3 causes little increase in bicarbonate secretion, as bile also contains bicarbonate and neutralises chyme, and brunners glands also secrete alkaline
- pH <5 causes a significant increase in pancreatic bicarbonate secretion
Describe the mechanism of pancreatic bicarbonate secretion
- Catalysed by carbonic acid, separation of hydrogen bicarbonate
- Na+ is moved down its gradient through paracellular tight junctions
- Water follows
- At the lumen, there is Cl/HCO3 exchange, with Na/H exchange at the basolateral membrane
- Na gradient maintained by sodium potassium pump
- Potassium is then returned to the blood by K channels
- Chloride is returned to the lumen via chloride channels
Where are enzymes for digestion of fat, proteins and carbohydrates synthesised and stored in the acinar cells?
Zymogen granules (proenzymes)
How are acinar cells protected from damage by enzymes it produces?
- Proteases released as proenzymes
- Trypsin inhibitor produced
- Enzymes are only activated in the duodenum
What happens when there is blockage of the pancreatic duct?
Blockage of the pancreatic duct results in auto-digestion (acute pancreatitis)
How are pancreatic enzyme functions controlled?
- Altered proportions due to diet
- Lack of enzymes and bile can result in malutrition even if diet is ok
How are pancreatic secretions controlled?
- Vagus nerve (cholinergic)
- Cephalic and gastric phase secretion due to ACth
- Intestinal phase (70-80% of pancreatic secretion) is hormonally controlled
- Bicarbonate controlled by secretin
- Enzyme secretion controlled by the vagal reflex and cholecystokinin
Compare the action in the cell of secretin and cholecystokinin
- Secretin uses cAMP
- Cholecystokinin controlled by Ca2+/PLC
How are CCK and secretin switched off?
- CCK swtiched off when the cepalic phase ends, and fats and peptides are removed
- Secretin is switched off when the pH increases
How do CCK and secretin act separately and interact?
- CCK alone has no effect on bicarbonate secretion, while it can increase bicarbonate secretion significantly once stimulated by secretin
- Secretin has no effect on enzyme secretion
