Pancreas Flashcards
Pancreas anatomy: describe the anatomical regions and functional acini of the pancreas Pancreas function: summarise the endocrine and exocrine functions of the pancreas Pancreatic regulation: explain how pancreatic function is controlled by nervous stimulation and hormonal regulation Pancreatitis: define acute and chronic pancreatitis; recall causes, symptoms and signs, investigations and complications
Describe the embryonic development of the pancreas.
Yellow blobs are the beginnings of the pancreas and create the ventral and dorsal bud, which become the ventral and dorsal parts of the pancreas. (Ventral bud is part of the original hepatobiliary bud, which buds out separately into the liver, ventral pancreas and gall bladder.)
During development, duodenum rotates, creating a C-shape below the stomach, moving the ventral and dorsal regions of the pancreas close together where they fuse. Ventral pancreas is the major pancreatic duct, and the dorsal region is the accessory pancreatic duct.
What are the five regions of the pancreas?
Islet (endocrine) tissue is most abundant in the tail.
What is the relative position of the pancreas?
Lies mainly posterior abdominal wall, extending from the C-shaped duodenum to hilum of the spleen.
The common bile duct runs anteriorly to It, at the head of the pancreas.
Posterior to the pancreas there is the IVC, abdominal aorta and left kidney.
What are the arteries that supply the pancreas? (x2)
Coeliac and superior mesenteric arteries.
What does endocrine and exocrine mean?
Endocrine: secretion into blood stream to have an effect on distant target organ.
Exocrine: secreting into a duct to have direct local effect – tends not to be something that goes around the body like endocrine.
What are the main endocrine secretions of the pancreas? (x3)
Insulin, glucagon, somatostatin.
What does insulin do?
ANABOLIC hormone that promotes glucose transport into cells, storage as glycogen, reduces blood glucose, promotes protein synthesis and lipogenesis.
What does glucagon do?
Increases gluconeogenesis and glycogenolysis – increases blood glucose.
What does somatostatin do?
‘Endocrine cyanide’ because it tends to suppress various processes depending on the tissue it affects, and suppresses secretion of other pancreatic hormones.
What are the relative proportions of exocrine and endocrine tissue in the pancreas?
Endocrine = 2% of the gland.
Exocrine = 98% of the gland.
How do the exocrine and endocrine regions of the pancreas develop?
Yellow regions turn into exocrine, and pink bits into islets – all originate from the same duct system. Over time, the endocrine regions lose their connections with the duct system, and sit independently as Islets (islands of endocrine tissue in the exocrine pancreatic tissue). Islets differentiate into their respective alpha and beta cells.
What are pancreatic acinar?
Functional unit of the EXOCRINE pancreas – grape-like clusters of secretory units which secrete pro-enzymes into the same duct.
What is the composition of Islets?
ALPHA CELLS (red): form about 20% of islet tissue and secrete GLUCAGON.
BETA CELLS (orange): form about 70% of islet tissue and secrete INSULIN.
DELTA CELLS: form about 10% of islet tissue and secrete SOMATOSTATIN.
Islets are highly vascular, ensuring that ALL endocrine cells have close access to site for secretion.
What does pancreas look like histologically? (x4 parts)
Paler regions are Islets. Dark regions are acini.
4 = small pancreatic duct which leads to main pancreatic duct.
What are the two components of pancreatic juice and where are they produced in the exocrine tissue?
ACINAR CELLS secrete enzymes – low volume, but viscous. Centroacinar cells to an extent also.
DUCT CELLS and CENTROACINAR CELLS secrete second component of pancreatic juice – do not have secretory granules, because they do not secrete enzymes. High volume, but watery. It is HCO3- rich.
What are the two functions of bicarbonate secretion?
Bicarbonate secretion – bicarbonate has high concentration and is alkaline (obviously).
It therefore NEUTRALISES acid chyme from stomach which prevents duodenal mucosa damage, and RAISES PH for optimum pH for pancreatic enzymes. It also WASHES low volume enzyme secretion our of the pancreas and into the duodenum.
How does rate of bicarbonate secretion respond to pH of incoming chyme from the stomach?
Levels below pH 3.
Mechanism of bicarbonate secretion? How are concentration gradients maintained?
- CO2 moves into the duct cells from the blood and reacts with water to produce HCO3- (and H+). Enzyme involved is carbonic anhydrase. HCO3- moves into duct lumen.
- HCO3- are pumped out AGAINST their concentration gradient and are exchanged with Cl- ions which move into duct cells DOWN their concentration gradient. This maintains electric gradients – important because if you did not maintain electric gradients, the processes would require more energy. Cl- gradients are maintained by Cl- channels which allows leakage of Cl- back into lumen.
- H+ are pumped out of the cell AGAINST their concentration gradient, by allowing exchange with Na+ which moves into cell DOWN concentration gradient. Na+ gradient is maintained by the Na+/K+ ATPase (found in every cell), and K+ gradient for ATPase pumping mechanism is maintained by leakage of K+ out of the duct cells into the blood using K+-channels.
- Duct tight junctions allow paracellular movement of Na+: Na+ moves into lumen down concentration gradient. This increases osmotic potential of the juice. This explains why the HCO3- secretion is low concentration and watery.
Describe the interaction between secretin and CCK (/vagus stimulation).
CCK alone has no effect on bicarbonate secretion.
Secretin increases bicarbonate secretion.
CCK and secretin together induces a HUGE increase in bicarbonate secretion. This means that CCK has a potentiating effect on secretin. The same occurs when secretin is complemented with vagus stimulation.
