Pancreas Flashcards
What is the pancreas derived from?
a foregut derivative - arises at foregut-midgut junction with dorsal and ventral buds
duodenum rotates to form central bud and ventral pancreas moves to lie adjacent to dorsal bud and both fuse
ventral duct = main pancreatic duct, dorsal = accessory
What is the functional anatomy of the pancreas?
uncinate, head, neck , body, tail islet tissue (endocrine) most abundant in the tail but endocrine and exocrine throughout
pancreas lies on posterior abdominal wall extends from C shaped duodenum to hilum of spleen
How does pancreatic juice reach duodenum?
via main and accessory pancreatic ducts
What are the main posterior relations of the pancreas?
Close relations and blood supply?
IVC, abdominal aorta, left kidney
coeliac and SMA (blood supply carries away endocrine hormones and fuels activity of pancreas during digestion
What are endocrine and exocrine glands?
endocrine - secretion into blood to have effect on distant target organ, ductless
exocrine - secretion into duct to have direct local effect
What is gastrin?
an autocrine hormone
What are the 2 functional parts of the pancreas?
endocrine 2%
- islets of langerhans
- secrete insulin, glucagon, somatostatin and pancreatic polypeptide into blood
- regulate blood glucose, metabolism, and growth effects
exocrine
- secrete pancreatic juice into duodenum via pancreatic duct/common bile duct
How is the duct system developed?
islets - endocrine components that eventually lose contact with the duct system and sit independently in the exocrine pancreas
- differentiate into a and b cells
acini and ducts - exocrine components
- acini are clusters of secretory units
- acinar cells secrete pro enzymes into ducts
What is the composition of islets?
a cells - 15-20%, glucagon
b cells - 60-70%, insulin
d cells - 5-10%, somatostatin
highly vascular so all endocrine cells have access to secretion sites
What are 2 components of pancreatic juice?
acinar cells - make low volume, viscous and enzyme rich
= contain secretory granules of enzymes
duct and centroacinar cells - high volume, watery, HCO3- rich
= smaller and paler
What is the function of bicarbonate secretion by centroacinar and duct cells?
juice rich in HCO3- = 120mM (plasma is 25mM) pH 7.5-8
- neutralise acid from stomach chyme
- prevent damage to duodenal mucosa
- raise pH to op range for pancreatic enzymes
- wash low volume acinar secretion out of pancreas to duodenum
What is the effect of duodenal pH on bicarbonate secretion rate?
ph <3 - not much more increase in HCO3 secretion
ph<5 linear increase in pancreatic bicarbonate secretion
emptying more stomach contents into duodenum cause increase water and HCO3 release to neutralise acid
Why does bicarbonate secretion stop when pH still acid?
bile also contains bicarbonate and helps neutralise chyme
brunners glands secrete alkaline fluid
What are the steps in HCO3 secretion?
- carbonic anhydrase in duct cell catalyses formation of H and HCO3
- separated products
- Na moved down [] gradient paracellularly and H2O follows
- Cl and HCO3 exchange at lumen
- H and Na exchange at basolateral membrane into bloodstream
- Na/K ATPase pump maintains Na gradient into cell (primary active transport)
- K+ and Cl- return to lumen via ion channels
What is the pH of gastric venous blood and pancreatic venous blood?
same reaction in parietal and duct cells
stomach - H+ to lumen and HCO3 to blood so blood is alkaline
pancreas - HCO3 to juice and H+ into blood so blood is acidic
How are enzymes stored in acinar cells?
in zymogen granules
zymogen = pro-enzyme
- inactive precursor to protect ducts and acini from autodigestion
- pancreas also has trypsin inhibitor to prevent trypsin activation
- enzymes only activated in duodenum
- blockage of pancreatic duct may overload protection and result in autodigestion (ACUTE PANCREATITIS)
What do lipase require in addition to colipase for effective action?
bile salts
How are pancreatic enzyme functions altered?
diet - high protein, low carb increase proteases, decreases amylases
pancreatic enzymes and bile are ESSENTIAL to digest meal - malnutrition (unlike salivary, gastric enzymes)
anti-obesity drug Orlistat inhibit pancreatic lipase - steatorrhea
When is steatorrhea commonly seen?
orlistat
chronic pancreatitis
cystic fibrosis
How is gut innervated?
vagus nerve
- cholinergic
- parasympathetic
- stomach constriction, peristalsis, increase pancreatic enzyme secretion
What are 3 phases of pancreatic secretion?
cephalic
- reflex response to smell,taste,sight of food
- enzyme rich component, low volume, little pancreas secretion
- enzyme release triggered by vagus nerve
ENDS WHEN MEAL EATEN
gastric
- stimulate pancreatic secretion from food arriving in stomach
intestinal
- 70/80% pancreatic secretion
- hormonally mediated when chyme enters duodenum
- enzyme and HCO3 components of pancreatic juice stimulated
How is bicarbonate secretion controlled?
release of hormone SECRETIN (cAMP)
How is enzyme secretion controlled?
vagal reflex and hormone cholcystokinin (CCK)
- reflex in cephalic and gastric pahse
- CCK release intracellularly and causes zymogen granules to use with membrane and release enzymes into pancreatic duct
What is the function of CCK (2)
- enzyme secretion
- bile secretion (contraction of smooth muscle sphincter around gall bladder)
Describe SECRETIN action?
- H+ in gastric chyme stimulates enteroendocrine cell (s cell) to release secretin
- these travel to pancreatic duct cells and cause intracellular cascade
- HCO3 is release
- travels in duct to duodenum to neutralise protons
- negative feedback - rising pH of duodenum stops secretin release
Describe CCK action?
- chyme peptides and fat stimulate c/i cells to produce CCK in the duodenum
- CCK enter blood and travels to acinus cells
- stimulates proenzyme and trypsin inhibitor release to enter duodenum
- Vagus (ACh) also stimulated acinus cell to release enzymes
How is CCK switched off?
absorption of fats/proteins removes local luminal stimulus for CCK release from mucosal c/i cells
How do CCK and secretin interact?
CCK alone - no effect on HCO3
with secretin markedly increase HCO3 production compared to secretin alone
secretin alone - no effect on enzyme secretion
vagus nerve acts like CCK to potentiate effect of secretin on HCO3 as we do not want too much acid in duodenum
we need large coupled effect
