Pancreas Flashcards
Pancreas development
Where does it arise?
What does it start as?
What happens during development?
Foregut-Midgut junction
Dorsal+ ventral buds (ventral= part of hepatobiliary bud)
Duodenum rotates to form a C shape, ventral bud swings round to lie adjacent to dorsal bud+ both buds fuse
Ventral bud duct becomes main pancreatic duct
Subdivisions of pancreas
Head (main duct comes out to go to duodenum) Neck Body Tail Uncinate (hook-like part)
Exocrine/ endocrine functions?
Both tissues throughout pancreas
More endocrine tissue in tail
How does pancreatic juice reach the duodenum?
By main+ accessory pancreatic duct
Anatomy
Where does it lie?
Posterior relations?
Blood supply from?
Posterior abdominal wall extending from C-shaped duodenum to hilum side of spleen
Inferior vena cava, abdominal aorta, left kidney
Coeliac+ superior mesenteric arteries
Endocrine secretion
Secretion into bloodstream to have effect on distant target organ (Autocrine/Paracrine) (acts as a ductless gland)
Exocrine secretion
Secretion into a duct to have a direct local effect
Endocrine secretions of pancreas+ actions
% of gland?
Parts of pancreas with this function?
Insulin= anabolic hormone (building up), promotes glucose transport into cells+ storage as glycogen, leads to reduce blood glucose+ promotes protein syntheis+ lipogenesis
Glucagon= Increases gluconeogenesis+ glycogenolysis= increase blood glucose
Somatostatin= Suppresses lots of things
2% of gland
Islets of Langerhans
Exocrine secretions of pancreas
% of gland?
What does it secrete? Via what?
98%
Pancreatic juice into duodenum via pancreatic duct/ common bile duct
Digestive function
Pancreatic disease affects?
Both exocrine+ endocrine functions
E.g. anyone with type 2 diabetes might also have exocrine problems
Pancreatic cell differentiation:
Exocrine?
Endocrine? Derived from? Which part of pancreas is it more common in?
Ducts, Acini (grape-like clusters of secretory units) that have acinar cells that secrete pro-enzymes into ducts
Derived from branching duct system, lose contact with ducts+ become islets, differentiate into α+ β cells secreting into blood
More common in tail than head
Exocrine secretion: Islets composition
Cells?
Secrete?
Property?
α cells- secrete glucagon
β cells- secrete insulin
δ cells- secrete somatostatin
Highly vascular= all endocrine cells have close access to a site for secretion
Acinar function
Acinar cells- secretory granules containing enzymes ready to be released
Duct cells- line the duct+ don’t have granules (don’t release enzymes)
Pancreatic juice components
Made which cells?
Purpose?
Low vol, viscous, enzyme rich fluid- acinar cells
High vol, watery, HCO3- rich alkaline fluid- Duct+ centroacinar cells
Neutralises acid chyme from stomach= prevents damage to duodenal mucosa+ raises pH optimum for pancreatic enzymes+ washes low volume enzyme secretion out of pancreas into duodenum (high vol.)
Effect of duodenal pH on bicarbonate secretion rate
Why does bicarbonate secretion stop when pH= still acidic?
As duodenal pH decreases, rate of bicarbonate secretion increases
Bile also contains bicarbonate+ helps neutralise acid chyme too (liver)+ Brunner’s glands secrete alkaline fluid (small intestine)
Mechanism of bicarbonate secretion Where is this occuring? Catalysed by? 4 steps Exchange driven by? Cystic fibrosis?
Duct cells
Carbonic anhydrase
1. Seperation of H+ and HCO3-
2. Na moves down gradient via tight junctions from blood to lumen= H20 follows
3. Cl-/HCO3 exchange at lumen (Cl- in, HCO3- out into lumen)
4. Na+/ H+ exchange at basolateral membrane into bloodstream (H+ out into blood, Na+ into cell)
5. Na gradient into cell from blood maintained by Na/K exchange pump using ATP (primary active transport)
6. K returns to blood via K+ channels
7. Cl returns to lumen via Cl- channels
Exchange driven by electrochemical gradients (Na+ Cl go along gradients)
Cystic fibrosis= Cl- channels dysfunctional= pancreatic cells can’t move Cl- into lumen= viscous enzyme rich secretion in ducts= trypsin activates+ cascade of protease activation= autodigestion of pancreatic cells= inflammation+ pancreatitis
H2CO3 in stomach vs pancreas
In stomach, H+ goes into gastric juice, HCO3- in blood therefore gastric venous blood= alkaline
In pancreas, HCO3- secreted into juice, H+ into blood therefore pancreatic venous blood is acidic
Therefore by intestine, neutralise each other
Enzyme secretion Cell type? Pro-enzymes name? Stored? Protease example? Pancreas blockage?
Acinar cells
Zymogens stored in zymogen granules
Proteases= inactive pro-enzymes= protection from auto-digestion
Trypsin inhibitor to prevent trypsin activation
Auto-digestion= acute pancreatitis in cystic fibrosis
Altered pancreatic enzyme function
Lack of enzymes=?
Adapt to diet (proteases+ amylases)
Lack= malnutrition
Olistat drug function
Side effects?
Used as?
Inhibits pancreatic lipases= inhbits intestinal fat absorption
Steatorrhoea- increased faecal fat
Weight loss agent
Control of secretion process
Nerve?
3 phases?
Vagus nerve- cholinergic via parasympathetic pathways to regulate gut function
Cephalic phase- reflex response to sensory innervation, enzyme rich component only, pancreas ‘mobilised’ more but not much else because food is still a long way. Phase ends when food= eaten
Gastric phase- stimulation of pacreatic secretion from food entering stomach, same mechanism as cephalic
Intestinal phase= most of pacreatic secretion, HORMONALLY mediated when gastric chyme enters duodenum, both components of pancreatic juice stimulated
Control of bicarbonate secretion
Occurs in which phase/s?
- Chyme comes into duodenum (acidic so contains H+)
- H+ in contact with S cells= enteroendocrine epithelial cell which secretes secretin when pH= under a certain level.
- Secretin travels around blood+ reaches pancreas
- Secretin binds to duct cells= increase cAMP= increased bicarbonate
- Increase pH= -ve feedback
Ocurrs in intestinal phase
Control of enzyme secretion
Occurs in which phase/s?
How is hormone switched off?
- Peptides+ fat in duodenum come into contact with C cells (enteroendocrine cells)= release Cholecystokinin (CCK) into blood
- CCK travels around circulation+ reaches acinus
- Acinus also stimulated by vagus reflex (ACh)
- Inctracellular cascade involving release of intracellular Ca2+ and Phospholipase C= granules fuse with membranes+ release contents into duct
- Acinus releases pro-enzymes+ trypsin inhibitor
CCK also stimulates bile secretion (liver)
Occurs in all phases
Absorption of fats+ peptides removes local stimulus for CCK release+ unknown mechanisms
CCK+ Secretin interaction CCK effect on bicarbonate? Vagus effect on bicarbonate? Secretin effect on enzyme? Reason?
No effect alone but bicarbonate secretion stimulated by secretin increases with CCK
Vagus nerve= no effect alone but bicarbonate secretion stimulated by secretin increases with CCK
Secretin= NO effect on enzyme secretion (CCK does it all)
Difference in arrangement of exocrine cells in liver and pancreas?
Liver= cells arranged linearly, secrete in canaliculi Pancreas= cells arranged in curved acini, secrete in ducts
