Pancreas

Question 1

What is the embryology of the pancreas?

Answer 1

1. Start as 2 separate ducts with buds (below duodenum):
   - Ventral —> connected to gall bladder and liver buds
   - Dorsal
2. Duodenum rotates clockwise and ducts fuse:
   - Major papilla = where ventral and dorsal duct fuse
   - Minor papilla = accessory pancreatic duct

Question 2

What are the 4 sections of the pancreas?

Answer 2

1. Head
2. Neck
3. Body
4. Tail

Question 3

Where is the pancreas?

Answer 3

Behind the stomach
In front of the kidneys, inferior vena cava and aorta

Question 4

How are images of the pancreas taken? (3)

Answer 4

1. CT scan with contrast
2. MRCP = Magnetic Resonance CholangioPancreatography
3. Angiograph —> in front of superior mesenteric artery

Question 5

What is endocrine secretion from the pancreas?

Answer 5

Secretion into the bloodstream —> 2%
- glands have no ducts —> islets
- effect on distant target organs
- regulate blood glucose, metabolism and growth

Question 6

What is exocrine secretion from the pancreas?

Answer 6

Secretion into a duct —> 98%
- glands have ducts —> acini
- direct local effect
- pancreatic juice —> digestive function

Question 7

What are the 3 main endocrine secretions of the pancreas?

Answer 7

1. Insulin
   - dec blood glucose
   - inc protein synthesis, inc lipogenesis
2. Glucagon
   - inc blood glucose
   - inc gluconeogenesis, inc glycogenolysis
3. Stomatostatin
   - inhibit GI and pancreatic secretions

Question 8

What are pancreatic acini? (2)

Answer 8

Endocrine secretory ducts
- Clusters of secretory units

1. Secretory acini - apical zymogen granules
   —> low vol, viscous, enzyme rich
2. Duct cells - small, pale cells around
   —> high vol, watery, HCO3- rich (also
   from centroacinar cells)

Question 9

What are pancreatic islets? (3)

Answer 9

Exocrine groups of cells —> highly vascular
- Derived from branching duct system —> lose contact with acini
- surrounded by acini

1. α-cells (15-20%) —> glucagon
2. β-cells (60-70%) —> insulin
3. δ-cells (5-10%) —> somatostatin

Question 10

What is the microanatomy of the pancreas?

Answer 10

1. Intralobular duct = main tubes
2. Intercalated duct = branches (ends —> centroacinar cells)
3. Acinus = cluster of pancreatic acinar cells
   - rER, golgi, zymogen granules (duct end)
   - intercellular canaliculi
   4 Islets of Langerhans - capillaries branch in

Question 11

What are the 2 functions of pancreatic juice?

Answer 11

Fluid from duct and centroacinar cells

1. Neuralises acid chyme —> high HCO3- (120mM, pH
   7.5-8.0)
2. Washes low volume enzyme secretion into
   duodenum

Question 12

How does duodenal pH affect pancreatic juice secretion?

Answer 12

pH < 5 —> linear inc in HCO3- secretion
pH < 3 —> plateau
- inc in HCO3- from bile
- Brunner’s glands secrete alkaline fluid

Question 13

How does pancreatic juice neutralise the acidic chyme? (5)

Answer 13

1. CO2 into pancreatic duct cell from blood —> reacts
   with H2O using carbonic anhydrase —> H+ + HCO3-
2. Na+ into lumen from blood via paracellular (tight)
   junctions + water follows —> low Na+ in blood
   (maintained by Na+/K+ ATPase)
3. HCO3- into lumen from cell via [AE] (HCO3-/Cl-
   anion exchanger) ∵ Cl- conc grad
4. H+ into blood from cell via [NHE-1] (H+/Na+
   exchanger)
5. K+ back to blood via K+ channel, Cl- back to lumen
   via [CFTR] (cystic fibrosis transmembrane
   conductance regulator)

Question 14

What is the difference in pH of gastric vs pancreatic venous blood and why?

Answer 14

Pancreatic —> acidic ∵ H+ pumped out
Stomach —> alkaline ∵ HCO3- pumped out

Question 15

When does acute pancreatitis occur?

Answer 15

MPD blockage —> overload protection of pancreas —> digestive enzymes leak out —> auto-digest pancreas

Question 16

Which 3 digestive enzymes are in pancreatic juice and what do they require?

Answer 16

1. Lipases - active when secreted but requires colipase
   (secreted as precursor) and bile salts
2. Proteases - trypsinogen to trypsin via enterokinase
   - all others activated by trypsin
3. 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

Question 17

What can alter pancreatic enzyme function? (2)

Answer 17

Physiological:
- contents of food
- drugs eg. Orlistat

Pathological:
- cystic fibrosis
- chronic pancreatitis

Question 18

What are the 3 phases of pancreatic juice secretion?

Answer 18

1. Cephalic Phase
   - reflex to sight/smell/taste of food
   - only enzyme rich component mobilised
2. Gastric Phase
   - when food enters stomach
   - only enzyme rich component mobilised
3. Intestinal Phase —> 70-80% secretion
   - when gastric chyme enters duodenum —> hormonal
   - both components of pancreatic juice secreted —>
   HCO3- + enough volume for enzymes out

Question 19

How is pancreatic juice enzyme secretion controlled? (2)

Answer 19

Acini:
- Vagus nerve —> ACh
- inhibits trypsin secretion —> inhibits
CCK secretion
- CCK = CholeCystoKinin
- from duodenal I cells
- amino acids and fatty acids stimulate CCK-RP

Question 20

How is pancreatic juice bicarbonate secretion controlled?

Answer 20

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)

Question 21

How do pancreatic secretions adapt to the food eaten?

Answer 21

1. low pH —> inc secretin
   - HCO3-
2. peptides + fats —> inc CCK and stimulate vagus n
   - enzymes (peak by 30mins —> till
   stomach empty)