Pancreas

Question 1

Pancreas development
Where does it arise?
What does it start as?
What happens during development?

Answer 1

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

Question 2

Subdivisions of pancreas

Answer 2

Head (main duct comes out to go to duodenum)
Neck
Body
Tail
Uncinate (hook-like part)

Question 3

Exocrine/ endocrine functions?

Answer 3

Both tissues throughout pancreas

More endocrine tissue in tail

Question 4

How does pancreatic juice reach the duodenum?

Answer 4

By main+ accessory pancreatic duct

Question 5

Anatomy
Where does it lie?
Posterior relations?
Blood supply from?

Answer 5

Posterior abdominal wall extending from C-shaped duodenum to hilum side of spleen
Inferior vena cava, abdominal aorta, left kidney
Coeliac+ superior mesenteric arteries

Question 6

Endocrine secretion

Answer 6

Secretion into bloodstream to have effect on distant target organ (Autocrine/Paracrine) (acts as a ductless gland)

Question 7

Exocrine secretion

Answer 7

Secretion into a duct to have a direct local effect

Question 8

Endocrine secretions of pancreas+ actions
% of gland?
Parts of pancreas with this function?

Answer 8

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

Question 9

Exocrine secretions of pancreas
% of gland?
What does it secrete? Via what?

Answer 9

98%
Pancreatic juice into duodenum via pancreatic duct/ common bile duct
Digestive function

Question 10

Pancreatic disease affects?

Answer 10

Both exocrine+ endocrine functions

E.g. anyone with type 2 diabetes might also have exocrine problems

Question 11

Pancreatic cell differentiation:
Exocrine?
Endocrine? Derived from? Which part of pancreas is it more common in?

Answer 11

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

Question 12

Exocrine secretion: Islets composition
Cells?
Secrete?
Property?

Answer 12

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

Question 13

Acinar function

Answer 13

Acinar cells- secretory granules containing enzymes ready to be released
Duct cells- line the duct+ don’t have granules (don’t release enzymes)

Question 14

Pancreatic juice components
Made which cells?
Purpose?

Answer 14

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.)

Question 15

Effect of duodenal pH on bicarbonate secretion rate

Why does bicarbonate secretion stop when pH= still acidic?

Answer 15

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)

Question 16

Mechanism of bicarbonate secretion
Where is this occuring?
Catalysed by?
4 steps
Exchange driven by?
Cystic fibrosis?

Answer 16

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

Question 17

H2CO3 in stomach vs pancreas

Answer 17

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

Question 18

Enzyme secretion
Cell type?
Pro-enzymes name? Stored?
Protease example?
Pancreas blockage?

Answer 18

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

Question 19

Altered pancreatic enzyme function

Lack of enzymes=?

Answer 19

Adapt to diet (proteases+ amylases)

Lack= malnutrition

Question 20

Olistat drug function
Side effects?
Used as?

Answer 20

Inhibits pancreatic lipases= inhbits intestinal fat absorption
Steatorrhoea- increased faecal fat
Weight loss agent

Question 21

Control of secretion process
Nerve?
3 phases?

Answer 21

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

Question 22

Control of bicarbonate secretion

Occurs in which phase/s?

Answer 22

1. Chyme comes into duodenum (acidic so contains H+)
2. H+ in contact with S cells= enteroendocrine epithelial cell which secretes secretin when pH= under a certain level.
3. Secretin travels around blood+ reaches pancreas
4. Secretin binds to duct cells= increase cAMP= increased bicarbonate
5. Increase pH= -ve feedback
   Ocurrs in intestinal phase

Question 23

Control of enzyme secretion
Occurs in which phase/s?
How is hormone switched off?

Answer 23

1. Peptides+ fat in duodenum come into contact with C cells (enteroendocrine cells)= release Cholecystokinin (CCK) into blood
2. CCK travels around circulation+ reaches acinus
3. Acinus also stimulated by vagus reflex (ACh)
4. Inctracellular cascade involving release of intracellular Ca2+ and Phospholipase C= granules fuse with membranes+ release contents into duct
5. 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

Question 24

CCK+ Secretin interaction
CCK effect on bicarbonate?
Vagus effect on bicarbonate?
Secretin effect on enzyme?
Reason?

Answer 24

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)

Question 25

Difference in arrangement of exocrine cells in liver and pancreas?

Answer 25

Liver= cells arranged linearly, secrete in canaliculi
Pancreas= cells arranged in curved acini, secrete in ducts