Pancreas Flashcards
Where does the pancreas develop from?
Foregut derivative arising at the foregut-midgut juntion. Dorsal and ventral buds, ventral bud is part of hepatobiliary bud
How is the pancreas subdivided?
Head, neck, body, tail and uncinate (latin for hook like) process
Where is islet tissue most abundant?
Tail
What are the main posterior relations to the pancreas?
IV, abdominal aorta and left kidney
What arteries have close relations with and supply the pancreas?
Coeliac and superior mesenteric arteries
Define endocrine?
Secretion into blood stream to have an effect on distant target organs (autocrine/paracrine) - ductless glands
Define exocrine?
Secretion into a duct to have a direct local effect
What are the main endocrine secretions of the pancreas?
Insulin, glucagon, somatostatin
What does insulin do?
Anabolic hormone that promotes glucose transport into cells and storage as glycogen. Reduces blood glucose, promotes protein synthesis and lipogenesis
What does glucagon do?
Increase gluconeogenesis and glycogenolysis (to increase blood glucose)
What does somatostatin do?
Endocrine cyanide
What is the endocrine part of the pancreas? What percentage of the pancreas is it?
Islets of langerhans. 2%
What does the endocrine part of the pancreas do?
Secretes hormones into blood - insulin and glucagon and regulates blood glucose, metabolism and growth effects
What does the exocrine part of the pancreas do?
Secretes pancreatic juice into duodenum via pancreatic duct/common bile duct
Digestive function
What percentage of the pancreas does exocrine actions?
98%
What kinds of pancreatic cells are involved in exocrine action?
Ducts and acini
What do acini look like?
Grape like clusters of secretory units
What do acinar cells secrete?
Pro-enzymes into ducts
What do endocrine cells become in pancreas?
Alpha and beta islets of langerhans
More in tails than head
Where do the endocrine pancreatic cells derive from?
Branching duct system
What are the composition of islets of langerhans (how much of there of each type of cell)
15-20% alpha cells
60-70% beta cells
5-10% delta cells
What do delta cells produce in islets of langerhans?
Somatostatin
Why must the islets of langerhans be highly vascular?
Ensure all endocrine cells have close access to a site for secretion
What are the two components of pancreatic juice?
Low volume of viscous, enzyme rich acinar cells
High volume of HCO3 rich duct and centroacinar cells
What is the point of the bicarbonate secretion in the pancreas?
Neutralises acid chyme from the stomach, preventing damage to duodenal mucosa and raises pH to optimum range for pancreatic enzymes to work
Where is the bicarbonate secreted from in the pancreas?
Duct and centroacinar cells
What else does the bicarb solution in the pancreas do other than neutralise?
Washes low vol enzyme secretion out of pancreas and into the duodenum
When does the pancreas secrete more bicarb?
When the pH is less than 5 but at less than 3 there is not much more increase in bicarb rate
Why does the bicarb secretion stop when the pH is still acid?
Bile also contains bicarb and helps neutralise the acid chyme in liver and brunners glands also secrete alkaline fluid in small intestine
What is the mechanism of bicarbonate secretion?
- Seperation H+ and HCO3- by carbonic anhydrase. Na+ down gradient via paracellular tight junctions and H2O follows
- exchange of Cl/HCO3 (lumen) and Na/H (basolateral memb) driven by electrochemical gradients
- Na gradient maintained using Na/K pump - atp primary active transport
- K returns to blood - K channel and Cl returns to lumen via Cl channel
What are zymogens
Pro-enzymes
Why are acinar cell enzymes secreted?
For digestion of fat (lipases), protein (proteases) and carbs (amylase)
Where are acinar cell enzyme secretions synthesised and stored?
In zymogen granules
What might be the problem for an organ making a cocktail of digestive enzymes
????????
What are proteases released as in pancreas? Why?
Inactive proenzymes
Protects acini and ducts from autodigestion
Where do the acinar cell enzyme secretion enzymes become activated?
Duodenum
What can a blockage of pancreatic duct do?
Overload protection and result in autodigestion = acute pancreatitis
What does the pancreas contain to prevent trypsin activation?
Trypsin inhibitor
Where does the enterokinases cleave the trypsinogen?
Between valine and isoleucine
What starts protein digestion?
Pepsin in the stomach in acid conditions
What happens when chyme enters duodenum from stomach?
Pepsin mixed into it, but is soon inactivated as alkaline conditions
What enzyme is secreted from what to convert typsinogen to trypsin?
Duodenal mucosa secretes an enzyme - enterokinase (enteropeptidase)
What does trypsin do?
Converts all other proteolytic and some lipolytic enzymes
What is special about lipase?
Lipase is secreted in active form but requires colipase which is secreted as a precursor
What is an anti obesity drug that inhibits pancreatic lipases?
Orlistat
hense reduce intestinal fat absorption
What are side effects to orlistat?
A pancreatic lipase inhibitor cauess:
Steatorrhoea
When does steatorrhea occur?
When pancreatic lipase secretion is significantly reduced eg in CF, chronic pancreatitis, orlistat
How is pancreatic secretion regulated? What nerve and what does it do?
Vagus nerve
Cholinergic
Communicates info from gut to brain
What happens in the 3 stages of food digestion but in the pancreas?
- cephalic phase - enzyme rich component only. Low vol - mobilises enzymes
- stimulation of pancreatic secretion, same mech as cephalic
- hormone mediated, gastric chyme enter duodenum and both components of pancreatic juice stimulated - enzymes and HCO3
How is bicarbonate secretion controlled in pancreas?
Release of hormone Secretin (cAMP)
How is enzyme secretion controlled in pancreas?
Vagal reflex and
Hormone - cholecystokinin (CCK) (Ca2+/PLC) - CCK also stimulate bile secretion
How is CCK switched off in pancreas?
Cephalic phase ends when meal eaten, absorption of fats and peptides removes local luminal stimulus for CK release from mucosa
What effect does CCK alone have on bicarbonate secretion in pancreas?
no effect
What effect does CCK and secretin together have on bicarb secretion in pancreas?
Markedly increase bicarb release
What effect does vagus nerve have on bicarb secretion in pancreas?
Similar lack of effect as CCK
What effect does secretin have on enzyme secretion in pancreas?
NO EFFECT
What stimulates release of secretin in pancreas?
H+ ions in duodenum stimulate realse, and also stimulate release of pancreatic juice to raise the pH
What causes a sharp CCK rise in pancreas
Peptides and fat in duodenum
