The pancreas

Question 1

describe the pancreatic development?

Answer 1

The dorsal and ventral buds arise from the foregut-midgut
junction with the ventral bud being part of the Hepatobiliary
bud

• The duodenum rotates into a c-shape and the ventral bud
  swings round adjacent to the dorsal bud and buds fuse.
• ventral bud duct then becomes the main pancreatic duct

-

Question 2

what is the pancreas split into?

Answer 2

uncinate, head, neck, body, tail.

Question 3

where is the islet tissue most abundant?

Answer 3

in the tail

the tail then extends to the hilum of the spleen

Question 4

what is the pancreas supplied by?

Answer 4

coeliac and superior

mesenteric arteries.

Question 5

define endocrine

define exocrine

Answer 5

Endocrine = secretion into blood stream, distant effect (2%)

Exocrine = secretion into duct, local effect [98%].(pancreatic juices)

Question 6

what does pancreatic disease involve?

Answer 6

exocrine AND endocrine effects

Question 7

what are the endocrine pancreatic cells?

Answer 7

• derived from duct system
• become islets
• differentiate into alpha, beta, delta cells
  alpha : glucagon
  beta : insulin
  delta: somatostatin

Question 8

what are the exocrine pancreatic cells?

Answer 8

• Arranged in ducts.
• Acini are grape-like clusters
  of secretory units
• they secrete pro enzymes into ducts

PANCREATIC JUICE

Question 9

what are the two components of the exocrine cells?

Answer 9

• acinar cells :LOW volume, VISCOUS,
  enzyme-RICH
• Duct and Centroacinar cells
  – HIGH
  volume, WATERY, HCO3
• RICH.

Question 10

what are the functions of pancreatic juice?

Answer 10

• Neutralise acidic chyme from stomach
• Prevents damage to duodenal mucosa.
• Raises pH so pancreatic enzymes can function.
• Wash low volume enzyme secretion out of pancreas.

Question 11

how does the rate of bicarbonate secretion change?

Answer 11

when the PH of the duodenum decreased the rate of bicarbonate increases

Question 12

why does it stop when PH is still acidic at PH 5?

Answer 12

Bicarbonate secretion ODDLY plateaus when pH is still acidic but
this is OK as: bicarbonate bile helps neutralise AND Brunner’s
glands found in sub-mucosa secrete alkaline still.

Question 13

what is the mechanism of bicarbonate secretion?

what antiporters are involved?

Answer 13

• Sodium moves down gradient via paracellular ‘tight’ junctions
• Water is drawn into the lumen by sodium raising lumen osmolarity.

Na+/H+ antiporter = secondary active transport

Cl-/HCO3
-antiporter = secondary active transport

‘Leak channels’ exist to allow chloride and potassium ions to
return back into the cell and blood respectively.

• This enables the pumping of bicarbonate to continue

Question 14

where are enzymes secreted in the acinar cells stored?

examples?

Answer 14

stored in zymogen granules

e.g lipases, proteases and amylases.

Question 15

what prevents the organ from auto digestion?

Answer 15

Proteases are released as inactive pro-enzymes (zymogens) which protects
the organ from auto-digestion

Question 16

what happens in acute pancreatitis ?

Answer 16

• fat necrosis.
• Pancreatic duct becomes blocked which may overload protection
  and result in auto-digestion.

Question 17

how is trypsinogen activated?

Answer 17

• The duodenal mucosa has enterokinase (enteropeptidase) which activates trypsin from tyrpsinogen.
• the trypsin then converts a host of other proteases

Question 18

why are the enzymes needed?

Answer 18

• without them might result in malnutrition

- Pancreatic enzymes adapt to the diet

Question 19

what are the three stages of secretion?

Answer 19

• cephalic stage
  vagal response to sight or smell
• gastric phase
  hormonal stimulation
• intestinal phase
  hormonally stimulated when the chyme enters the dueodenum

Question 20

what is bicarbonate secretion controlled by?

Answer 20

release of HORMONE – Secretin

Question 21

what is enzyme secretion controlled by?

Answer 21

Enzyme secretion controlled by VAGAL REFLEX and by a HORMONE – Cholecystokinin

Question 22

how is the bicarbonate secretion controlled?

Answer 22

• high PH means protons bind to the secretin receptor and stimulate secretin release into the blood
• meaning more bicarbonate is released
• when there is a higher PH the feedback is switched off

Question 23

how is enzyme secretion controlled?

Answer 23

• Vagus stimulation directly to acinus stimulates zymogen release.
• high conc of peptides stimulates C receptor that stimulates CCK release into the blood that acts on the acinus in the same fashion.

Question 24

when is CCK release stopped?

Answer 24

• the end of the cephalic phase

- no local stimulus from fats / peptides

Question 25

what combination has an effect on bicarbonate secretion?

Answer 25

- CCK alone does not have an effect on bicarbonate - secretin has some effect - CCK and secretin has a great effect on bicarbonate secretion

Question 26

over all what happens during a meal?

Answer 26

- food is mixed and digested in stomach - chyme is squirted into duodenum - H + ions stimulate secretin release which stimulates release of pancreatic juices - peptides and fats cause a sharp rise in CCK and vagal nerve stimulation - meaning the pancreatic enzymes are released - bicarbonate is then released due to CCK and secretin