Pancreas Flashcards
(21 cards)
What is the embryology of the pancreas?
- Start as 2 separate ducts with buds (below duodenum):
- Ventral —> connected to gall bladder and liver buds
- Dorsal - Duodenum rotates clockwise and ducts fuse:
- Major papilla = where ventral and dorsal duct fuse
- Minor papilla = accessory pancreatic duct
What are the 4 sections of the pancreas?
- Head
- Neck
- Body
- Tail
Where is the pancreas?
Behind the stomach
In front of the kidneys, inferior vena cava and aorta
How are images of the pancreas taken? (3)
- CT scan with contrast
- MRCP = Magnetic Resonance CholangioPancreatography
- Angiograph —> in front of superior mesenteric artery
What is endocrine secretion from the pancreas?
Secretion into the bloodstream —> 2%
- glands have no ducts —> islets
- effect on distant target organs
- regulate blood glucose, metabolism and growth
What is exocrine secretion from the pancreas?
Secretion into a duct —> 98%
- glands have ducts —> acini
- direct local effect
- pancreatic juice —> digestive function
What are the 3 main endocrine secretions of the pancreas?
- Insulin
- dec blood glucose
- inc protein synthesis, inc lipogenesis - Glucagon
- inc blood glucose
- inc gluconeogenesis, inc glycogenolysis - Stomatostatin
- inhibit GI and pancreatic secretions
What are pancreatic acini? (2)
Endocrine secretory ducts
- Clusters of secretory units
- Secretory acini - apical zymogen granules
—> low vol, viscous, enzyme rich - Duct cells - small, pale cells around
—> high vol, watery, HCO3- rich (also
from centroacinar cells)
What are pancreatic islets? (3)
Exocrine groups of cells —> highly vascular
- Derived from branching duct system —> lose contact with acini
- surrounded by acini
- α-cells (15-20%) —> glucagon
- β-cells (60-70%) —> insulin
- δ-cells (5-10%) —> somatostatin
What is the microanatomy of the pancreas?
- Intralobular duct = main tubes
- Intercalated duct = branches (ends —> centroacinar cells)
- Acinus = cluster of pancreatic acinar cells
- rER, golgi, zymogen granules (duct end)
- intercellular canaliculi
4 Islets of Langerhans - capillaries branch in
What are the 2 functions of pancreatic juice?
Fluid from duct and centroacinar cells
- Neuralises acid chyme —> high HCO3- (120mM, pH
7.5-8.0) - Washes low volume enzyme secretion into
duodenum
How does duodenal pH affect pancreatic juice secretion?
pH < 5 —> linear inc in HCO3- secretion
pH < 3 —> plateau
- inc in HCO3- from bile
- Brunner’s glands secrete alkaline fluid
How does pancreatic juice neutralise the acidic chyme? (5)
- CO2 into pancreatic duct cell from blood —> reacts
with H2O using carbonic anhydrase —> H+ + HCO3- - Na+ into lumen from blood via paracellular (tight)
junctions + water follows —> low Na+ in blood
(maintained by Na+/K+ ATPase) - HCO3- into lumen from cell via [AE] (HCO3-/Cl-
anion exchanger) ∵ Cl- conc grad - H+ into blood from cell via [NHE-1] (H+/Na+
exchanger) - K+ back to blood via K+ channel, Cl- back to lumen
via [CFTR] (cystic fibrosis transmembrane
conductance regulator)
What is the difference in pH of gastric vs pancreatic venous blood and why?
Pancreatic —> acidic ∵ H+ pumped out
Stomach —> alkaline ∵ HCO3- pumped out
When does acute pancreatitis occur?
MPD blockage —> overload protection of pancreas —> digestive enzymes leak out —> auto-digest pancreas
Which 3 digestive enzymes are in pancreatic juice and what do they require?
- Lipases - active when secreted but requires colipase
(secreted as precursor) and bile salts - Proteases - trypsinogen to trypsin via enterokinase
- all others activated by trypsin - Amylase
To protect acini and ducts from enzymes:
- all synthesised and stored in zymogen (pro-enzyme) granules —> activated only in duodenum
- trypsin inhibitor in pancreas
What can alter pancreatic enzyme function? (2)
Physiological:
- contents of food
- drugs eg. Orlistat
Pathological:
- cystic fibrosis
- chronic pancreatitis
What are the 3 phases of pancreatic juice secretion?
- Cephalic Phase
- reflex to sight/smell/taste of food
- only enzyme rich component mobilised - Gastric Phase
- when food enters stomach
- only enzyme rich component mobilised - Intestinal Phase —> 70-80% secretion
- when gastric chyme enters duodenum —> hormonal
- both components of pancreatic juice secreted —>
HCO3- + enough volume for enzymes out
How is pancreatic juice enzyme secretion controlled? (2)
Acini:
- Vagus nerve —> ACh
- inhibits trypsin secretion —> inhibits
CCK secretion
- CCK = CholeCystoKinin
- from duodenal I cells
- amino acids and fatty acids stimulate CCK-RP
How is pancreatic juice bicarbonate secretion controlled?
Duct and centroacinar cells:
- Secretin —> stimulates H2O and HCO3- release
(HCO3-/Cl- exchanger) —> isotonic
acinar fluid picks up H2O and HCO3- on
way out
—> further HCO3- inc with CCK
- from S cells
- inhibited by higher pH in duodenum (-ve
feedback)
How do pancreatic secretions adapt to the food eaten?
- low pH —> inc secretin
- HCO3- - peptides + fats —> inc CCK and stimulate vagus n
- enzymes (peak by 30mins —> till
stomach empty)
