The pancreas Flashcards
describe the pancreatic development?
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
-
what is the pancreas split into?
uncinate, head, neck, body, tail.
where is the islet tissue most abundant?
in the tail
the tail then extends to the hilum of the spleen
what is the pancreas supplied by?
coeliac and superior
mesenteric arteries.
define endocrine
define exocrine
Endocrine = secretion into blood stream, distant effect (2%)
Exocrine = secretion into duct, local effect [98%].(pancreatic juices)
what does pancreatic disease involve?
exocrine AND endocrine effects
what are the endocrine pancreatic cells?
- derived from duct system
- become islets
- differentiate into alpha, beta, delta cells
alpha : glucagon
beta : insulin
delta: somatostatin
what are the exocrine pancreatic cells?
- Arranged in ducts.
- Acini are grape-like clusters
of secretory units - they secrete pro enzymes into ducts
PANCREATIC JUICE
what are the two components of the exocrine cells?
- acinar cells :LOW volume, VISCOUS,
enzyme-RICH - Duct and Centroacinar cells
– HIGH
volume, WATERY, HCO3 - RICH.
what are the functions of pancreatic juice?
- 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.
how does the rate of bicarbonate secretion change?
when the PH of the duodenum decreased the rate of bicarbonate increases
why does it stop when PH is still acidic at PH 5?
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.
what is the mechanism of bicarbonate secretion?
what antiporters are involved?
- 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
where are enzymes secreted in the acinar cells stored?
examples?
stored in zymogen granules
e.g lipases, proteases and amylases.
what prevents the organ from auto digestion?
Proteases are released as inactive pro-enzymes (zymogens) which protects
the organ from auto-digestion
what happens in acute pancreatitis ?
- fat necrosis.
- Pancreatic duct becomes blocked which may overload protection
and result in auto-digestion.
how is trypsinogen activated?
- The duodenal mucosa has enterokinase (enteropeptidase) which activates trypsin from tyrpsinogen.
- the trypsin then converts a host of other proteases
why are the enzymes needed?
- without them might result in malnutrition
- Pancreatic enzymes adapt to the diet
what are the three stages of secretion?
- cephalic stage
vagal response to sight or smell - gastric phase
hormonal stimulation - intestinal phase
hormonally stimulated when the chyme enters the dueodenum
what is bicarbonate secretion controlled by?
release of HORMONE – Secretin
what is enzyme secretion controlled by?
Enzyme secretion controlled by VAGAL REFLEX and by a HORMONE – Cholecystokinin
how is the bicarbonate secretion controlled?
- 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
how is enzyme secretion controlled?
- 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.
when is CCK release stopped?
- the end of the cephalic phase
- no local stimulus from fats / peptides
what combination has an effect on bicarbonate secretion?
- CCK alone does not have an effect on bicarbonate
- secretin has some effect
- CCK and secretin has a great effect on bicarbonate secretion
over all what happens during a meal?
- 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
