Pancreas And Small Bowel Flashcards
Describe the embryological development of the pancreas
1) Abdominal accessory organs arise as foregut outgrowths
2) Proximal duodenum rotates clockwise- all organs are in their place by 11 weeks
3) Ventral and dorsal pancreatic buds and ducts fuse- the ducts form the major papilla . Bile and pancreatic ducts join to drain together at major papilla
There’s also a minor papilla which has been degraded away in many adults
Pancreatic duct at major papilla joins with distal common bile duct to form the ampulla
What 2 ducts join at the major papilla?
pancreatic duct
Bile duct
What is the uncinate process of the pancreas originated from?
Ventral bud and duct
What do the ventral and dorsal ducts emerge as respectively?
Ventral - Main pancreatic duct at the major papilla
Dorsal - Accessory pancreatic duct at the minor papilla
the accessory pancreatic duct present in everyone?
No in most adults it has been degenerated
What does the fact the the pancreas is a retroperitoneal structure mean?
does not exist within the abdomen
It is behind the posterior to the peritoneum
MRCP imaging diagram and when is it used?
Magnetic Resonance CholangioPancreatography
Procedure can be used to determine whether gallstones are lodged in any of the ducts surrounding the gallbladder
Uses magnetic resonance imaging to visualise the biliary and pancreatic ducts non-invasively
Can’t see pancreatic duct
Angiography diagrams and when is it used?
Angiography - accessing femoral artery, put needle in and thread wire via femoral artery to aorta. Then put dye into the coeliac axis
When patients are bleeding
What is pancreas divisum and why does it cause the patient to have recurrent episodes of pancreatitis?
Ventral bud and dorsal buds fail to fuse and so the ventral duct which usually has a large enough capacity to cope with the flow of the pancreatic juice can no longer do so
The large flow has to therefore go through a minor duct and so they get recurrent episodes of pancreatits
Define endocrine vs exocrine secretion
Endocrine- secretion into bloodstream to have effect on distant target organ (ductless glands)
Exocrine- secretion into a duct to have direct local effect
What are the 3 main endocrine secretions of the pancreas and their actions?
- 2% of gland secretions are endocrine through islets of Langerhans
- Insulin- anabolic hormone that promotes glucose transport into cells and storage as glycogen, decreases blood glucose, promotes protein synthesis and lipogenesis
- Glucagon- increases gluconeogenesis and glycogenolysis (increases blood glucose)
- Somatostatin- inhibits everything- known as ‘endocrine cyanide’
What are the main exocrine secretions of the pancreas and their actions?
- Secretes pancreatic juice into duodenum via main pancreatic duct/sphincter of Oddi/ampulla
- Exocrine acinar cells
- Digestive function
- What is the composition of the islets?
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- Alpha cells (A) form 15-20% of islet tissue and secrete glucagon
- Beta cells (B) form 60-70% of islet tissue and secrete insulin
- Delta cells (D) form 5-10% of islet tissue and secrete somatostatin
Why are Islets highly vascular
so all endocrine cells have close access to site for secretion
What is the composition of acini
- Secretory acinar cells- large with apical secretion granules
- Duct cells- small and pale
- Acini secrete their enzymes into ducts
What are the 2 components of pancreatic juice and what are they produced by?
1) Acinar cell makes low volume, viscous, enzyme-rich part of the juice
2) Duct and centroacinar cells make high volume, watery, HCO3- rich part of juice
What are the (2) functions of the bicarbonate secretion in the pancreatic juice?
Increases pH of the juice to 7.5-8
- Neutralises acid chyme from stomach, what does this do (2)Prevents damage to duodenal mucosaRaises pH to optimum range for pancreatic enzymes to work
- Washes low volume enzyme secretion out of pancreas into duodenum
What is the effect of duodenal pH on HCO3- secretion rate?
When duodenal pH < 5 → there’s linear increase in pancreatic HCO3- secretion
Why does HCO3- secretion stop increasing when duodenal pH goes below 3 (2 reasons)?
- Bile also contains HCO3- and helps neutralise acid chyme
- Brunners glands secrete alkaline fluid
Describe the mechanism of bicarbonate release and action by pancreas
1) CO2 moves into pancreatic duct cell from blood and reacts with H2O (catalysed by carbonic anhydrase) to form H+ and HCO3- which are separated
2) Na+ and H2O move down gradient via paracellular ‘tight’ junctions, into lumen
3) Cl- and HCO3- are exchanged at pancreatic lumen through anion exchanger (AE1) → Cl- movement driven by electrochem grad
4) Na+/H+ exchange at basolateral membrane into bloodstream happening through sodium-hydrogen exchanger (antiporter) type 1 (NHE-1) → Na+ enters the cell down gradient
5) Na+ gradient into cell from blood maintained by Na+/K+ exchange pump → uses ATP to transport Na+ out of cell and K+ into cell
6) K+ returns to blood via K+ channel and Cl- returns to lumen via Cl- channel (CFTR), to maintain their electrochemical gradients.
How is the bicarbonate reaction used differently in stomach and pancreas? (i.e. state the difference in venous blood of the stomach and venous blood of the pancreas, and explain why)
- In stomach, H+ formed is secreted into gastric juice and HCO3- is secreted into blood so gastric venous blood is alkaline
- In pancreas, H+ formed is secreted into blood and HCO3- is secreted into pancreatic juice so pancreatic venous blood is acidic
Which 3 classes of digestive enzymes are present in the acinar cell enzyme secretion and in what form are they initially stored as?
- Lipases, proteases and amylase
- Synthesised and stored in zymogen (pro-enzyme) granules
Why are proteases released as inactive pro-enzymes?
Protects acini and ducts from auto-digestion
- Blockage of main pancreatic duct may overload protection leading to auto-digestion and acute pancreatitis
What other protective mechanisms against auto-digestion of the pancreas are there (2)
Pancreas contains trypsin inhibitor to prevent trypsin activation
Enzymes only activated in the duodenum - where they have to start digesting food
Trypsin converts all other proteolytic and some lipotyic enzymes into active form