Pancreas

Question 1

Describe the embryology of the pancreas

Answer 1

There is a ventral and dorsal pancreatic bud, the bile duct enters the ventral bud

Proximal duodenum rotates clockwise

The ventral and dorsal pancreatic buds and ducts fuse

Bile and pancreatic ducts join to drain together at major papilla

Question 2

Where is the pancreas located

Answer 2

Behind the Duodenum and stomach

Question 3

How can you ‘image’ the pancreas?

Answer 3

CT and MRCP, angiography scan

Question 4

What are acini?

Answer 4

Ducts

Acini are grape-like clusters of secretory units

Acinar cells secrete pro-enzymes into ducts

Question 5

What are Islet cells?

Answer 5

Derived from the branching duct system

Lose contact with ducts – become islets

Differentiate into α- and β-cells secreting into blood
Tail > head

Question 6

What do the following Islet cells secrete?
Alpha
Beta
Delta

Answer 6

Glucagon
Insulin
Somatostatin

• The islets are highly vascular, ensuring that all endocrine cells have close access to a site for secretion

Question 7

What do Duct cells look like?

Answer 7

Small and pale

Question 8

What are the two componants of pancreatic juice?

Answer 8

Acinar cells - low volume, viscous, enzyme rich

Duct and centracinar cells : high volume, HCO3- rich, watery,

Question 9

What produces pancreatic juice?

Answer 9

Duct and centroacinar cells

• pancreatic juice increases bicarbonate

Question 10

What do pancreatic juices do?

Answer 10

Neutralises acid chyme from stomach
prevents damage to duodenal mucosa
Raises pH to optimum range for pancreatic enzymes to work

Washes low volume enzyme secretion out of pancreas into duodenum

Question 11

Why does HCO3- secretion stop when pH is still acid?

Answer 11

Bile also contains HCO3- and helps neutralise acid chyme (liver functions lecture).

Brunners glands in duodenum secrete alkaline fluid (Small intestine lecture).

Question 12

How is HCO3- secreted by the pancreas?

Answer 12

Catalysed by carbonic anhydrase

Separation of H+ & HCO3-:
HCO3- leaves the duct cell into lumen and CL- moves in
H+ ions leave as Na+ move in through transporter into blood

Na+ moves down gradient via paracellular (“tight”) junctions from blood to lumen by passing the cell
H2O follows

Question 13

How is the sodium ion gradient from the blood to pancreatic duct cell maintained?

Answer 13

by Na+/K+ exchange pump
Uses ATP - Primary active transport

Potassium then returns to blood and chloride returns to lumen through its own transporter

Question 14

How can the same reaction cause differing pH environments?

H2O + CO2 –> H2CO3 –> H+ + HCO3-

Answer 14

Same reaction in gastric parietal cells (acid) and pancreatic duct cells (alkaline)

Stomach: H+ –> gastric juice

HCO3- –> blood

Pancreas: H+ –> Blood

HCO3- –> juice

Question 15

What are zymogen granules?

Answer 15

Pro-enzymes.

Synthesises and stores enzymes for digestion

Question 16

How does the pancreas keep itself safe from the digestive enzymes?

Answer 16

Proteases are released as inactive pro-enzymes
protects acini & ducts from auto-digestion

Pancreas also contains a trypsin inhibitor to prevent trypsin activation

Enzymes only activated in duodenum

Question 17

What is acute pancreatitis?

Answer 17

Blockage of Main pancreatitic duct (gallstone) may overload protection → auto-digestion (= acute pancreatitis)

Question 18

What enzyme does dudenal mucosa secrete?

Answer 18

Enterokinase (enteropeptidase)
converts trypsinogen → trypsin.

• brush border enzyme

Question 19

What does trypsin do?

Answer 19

then converts all other proteolytic & some lipolytic enzymes

Lipase secreted in active form but requires colipase (i.e. secreted as precursor)

lipases require presence of bile salts for effective action - see liver sessions

• so will prevent auto-damage

Question 20

Anti-obesity drug Orlistat inhibits pancreatic lipases – what side effects might you expect?

Answer 20

↑ faecal fat
occurs when pancreatic lipase secretion ↓

e.g. cystic fibrosis, chronic pancreatitis, Orlistat (↓s intestinal fat absorption)

Stathorrhea

Question 21

How many phases are there to the control of pancreatic juice secretion?

Answer 21

3 :

Cephalic phase

Gastric phase

Intestinal phase

Question 22

What occurs during the Cephalic phase?

Answer 22

Reflex response to sight/smell/taste of food
Enzyme-rich component only.
Low volume - “mobilises” enzyme

Question 23

What occurs during the gastric phase?

Answer 23

Stimulation of pancreatic secretion originating from food arriving in the stomach
Same mechanisms involved as for cephalic phase

Question 24

What occurs during the Intestinal phase?

Answer 24

phase (= 70-80% of pancreatic secretion)

Hormonally mediated when gastric chyme enters duodenum.
BOTH components of pancreatic juice stimulated * both from acinar and duct cells
enzymes & HCO3- juice flows into duodenum

Question 25

What controls the release of pancreatic juice enzyme secretion in acini?

Answer 25

• Vagus nerve –
  Cholinergic
  Vagal stimulation of enzyme secretin (& communicates information from gut to brain)
• Cholecystokinin (CCK) (Ca2+/PLC)

Question 26

What controls the release of bicarbonate secretion in in duct and centroacinar cells?

Answer 26

Secretin (cAMP) hormone

Question 27

Why is secretin stimulated secretion of H2O and HCO3- richer in concentration than acinar secretion?

Answer 27

because of Cl−/HCO3−exchange

Question 28

Negative feedback for HCO3-?

Answer 28

Decreased pH –> stimulate Secretin cells –> secretin release –> increases secretion of pancreatic juice increasing pH

Question 29

Does CCK have an effect on HCO3-?

Answer 29

Not if it works alone

It can increase stimulation which has already been activated by secretin

Vagus nerve has similar effect to CCK

Secretin NO EFFECT on enzyme secretion