AS Lecture 6 - The Pancreas Flashcards
What is the shape of pancreas?
Subdivided into head, neck, body, tail, and uncinate process
How does the pancreatic juice reach the duodenum?
Via main and accessory pancreatic ducts
What are the main posterior relations of the pancreas?
IVC, abdominal aorta and left kidney
How do you define endocrine and exocrine secretions?
Endo - to blood stream, carried by blood to distant target organs Exo - through duct, to nearby tissue
What are the main secretions of the pancreas and their actions?
Insulin - reduces BGL Glucagon - Increases BGL Somatostatin - Regulates alpha/beta cells in IoL
What is the endocrine functional part of the pancreas and what does it do?
Islets of Langherhans: secretes hormones into blood (insulin, glucagon, somatostatin and pancreatic polypeptide), regulation of blood glucose, metabolism and growth effects
What is the exocrine functional part of the pancreas and what does it do?
98% of gland - secretes pancreatic juice into duodenum via pancreatic duct/common bile duct, digestive function
How are the pancreatic cells differentiated?
Exo: ducts - acini (grape-like clusters of secretory units), acinar cells secrete proenzymes into ducts Endo: Derived from branching duct system, lose contact with ducts - becoming islets, differentiate into alpha and beta cells secreting into blood
What is the composition of the Islets of Langherhans?
Alpha cells-secrete glucagon > 15-20% Beta cells secrete insulin > 60-70% Delta cells secrete somatostatin > 5-10%
What are the 2 components of pancreatic juice?
Low vol, viscous, enzyme rich from acinar cells Duct and centroacinar cells release high vol, watery, HCO3 rich juice
What is the bicarbonate secretion made from?
Rich in bicarbonate, alkaline pH
Why does bicarbonate secretion stop when pH is still acid (pH 5)?
Bile also contains bicarbonate, and helps neutralise the acid chyme Brunner’s glands secrete alkaline fluid
What is the first step in bicarbonate secretion?
Catalysed by carbonic anhydride, separation of H+ and HCO3-, Na+ moves down gradient via para cellular junctions, then H2O follows.
What is the second step in bicarbonate secretion?
Cl/HCO3 exchange at lumen, Na/H exchange at basolateral membrane into bloodstream Exchange is driven by electrochemical gradient as high ec Na, high Cl in lumen compared to intracellular
What is the third step in bicarbonate secretion?
Na gradient into cell from blood maintained by Na/K pump, uses ATP so 1ry active transport
What is the fourth step in bicarbonate secretion?
K returns to blood via K channel and Cl returns to lumen via Cl channel
How are enzymes stored and released in acinar cells?
Enzymes for digestion of fat, proteins and carbs are synthesised and stored in zymogen granules
How is trypsin activated and what effect does that have on the other proteases released?
Enterokinase (duodenal brush border) breaks down trypsinogen into trypsin which then activates other proteins
How can pancreatic enzyme secretion change and what effect does this have?
Pancreatic secretion adapts to diet, but pancreatic enzymes are essential for normal digestion of a meal and lack of these can lead to malnutrition
What is steatorrhoea?
Increased faecal fat which occurs when pancreatic lipase secretion significantly reduced
How is pancreatic secretion controlled?
Vagus nerve - cholinergic, and communicates info from gut to brain
What are the phases of control of secretion and what happens in each phase?
Initial cephalic phase - reflex response to smell/thought of food, enzyme rich component only, low volumes so mobilises enzymes Gastric phase - Stimulation of pancreatic secretion originating from food arriving in the stomach (same as cephalic phase) Intestinal phase - hormonally mediated when gastric chyme enters duodenum, w/both components of pancreatic juice stimulated
How are the bicarbonate and enzymatic secretions controlled?
Both components separately controlled Bicarbonate controlled by Secretin (cAMP) Enzyme secretion controlled by vagal reflex and by Cholecystokinin (Ca2+/PLC)
What other functions does cholecystokinin have?
Also stimulates bile secretion
How is bicarbonate secretion controlled?
S cells have chemosensors in duodenum lining, which detect the pH of duodenum, and secrete secretin in blood, which travel to pancreatic duct, form HCO3 -> has a negative feedback component
How is enzyme secretion to the duodenum from the pancreas controlled?
C cells on duodenum wall, secrete CCK when they detect peptides and fats, which is carried to pancreas, attach to acinar cells and they secrete proenzymes and lipases Vagus nerve also sends signal to inhibit release of proenzymes
How is cholecystokinin switched off?
Turns off when meal eaten, absorption of fats and peptides removes local luminal stimulus for CCK release from mucosa
How do CCK, vagus nerve and secretin interact together to increase bicarbonate secretion?
CCK alone doesn’t affect bicarbonate secretion CCK can markedly increase bicarbonate secretion that has been stimulated by secretin Vagus nerve has the same effect as CCK Secretin has NO EFFECT on enzyme secretion
How is the pancreas developed in the embryo?
A foregut derivative arising at foregut-midgut junction Duodenum forms a c shape, ventral bud swings round to lie adj to the dorsal bud and both fuse together Ventral bud duct becomes the main pancreatic duct
Where is the islet tissue most abundant?
In the tail
Fill in the blanks of the pancreas divisions
Where does the pancreas lie in the body?
Mainly on posterior abdominal wall extending from C-shaped duodenum to hilum of spleen
What are the close relations of the pancreas?
Coeliac and superior mesenteric artery
What is an adapted feature of the islets of Langherhans for endocrine function?
Highly vascular ensuring that all endocrine cells have close access to a site for secretion
What is the function of the bicarbonate secretion?
Neutralises acidic chyme from stomach: preventing damage to duodenal mucosa, raises pH to optimum range for pan enzymes to work Washes low vol enzyme secretion out of pancreas into duodenum
Where is the bicarbonate secretion secreted from?
Duct and centroacinar cells
What would happen if the CFTR was defective when dealing with pancreatic HCO3 secretion?
Without CFTR, the pancreatic juices become less liquid, and can cause big problems, especially the breakdown of the pancreas
How are proteases and trypsin released from acinar cells?
Proteases released as inactive proenzymes, protects acini and ducts from auto digestion Trypsin inhibitor present to prevent trypsin activation Enzymes activated ONLY in duodenum
What happens if the pancreatic duct is blocked?
May overload protection resulting in auto-digestion, a.k.a. acute pancreatitis
