Secretion in the pancreas and intestines Flashcards
Describe some of the functions of the pancreas
Produces enzymes for digestion of nutrients
Achieving optimum pH in small intestine
Regulates fed and fasted states
What is the pancreas divided into?
Lobules
Describe the network of ducts in the pancreas
Lobules drain into intralobular ducts, into interlobular ducts and into a main duct
What does the pancreatic duct merge with?
The bile duct
Where do the pancreatic products enter the duodenum?
Duodenal papilla
What controls secretion into the duodenum?
The sphincter of Oddi
What is the functional secretory unit of the pancreas?
An acinus (and a small intercalated duct)
What makes up an acinus?
A cluster of acinar cells
What do acinar cells secrete?
Zymogens
Digestive enzymes
Isotonic plasma-like fluid
How are acinar cells specialised for their role?
Large number of RER and secretory vesicles
What is a centroacinar cell?
The cells at the junction of the duct cells and acinar cells
What do goblet cells do?
Produce mucus
What is the purpose of mucus?
Lubrication
Hydration
Mechanical protection
Immunological role
How are acinar cells stimulated?
Through CCK and muscarinic acetylcholine receptors
Located on the basolateral cell membrane
What pathway leads to secretion from an acinar cell?
Phospholipase C (PLC/PKC)/Ca2+ signal-transduction pathway
What is the second method of activating an acinar cell?
VIP and secretin activate adenylyl cyclase, leading to the production of cAMP and the activation of PKA
What is the primary function of the pancreatic duct cell?
Secrete HCO3- that alkalinises and hydrates the enzymes secreted by the acinar cells
What stimulates pancreatic duct cells?
Secretin (mainly)
Ach (a little)
By what method is HCO3- secreted?
A HCO3-/Cl- exchanger
Which anion channel allows Cl- to diffuse into the lumen?
The cystic fibrosis transmembrane conductance regulator (CFTR)
What produces secretin?
S cells
What is secretin produced in response to?
Duodenal acidification
What problems may someone with cystic fibrosis encounter in the pancreas?
Faulty CFTR channels
Decreased secretion of HCO3- and water by the pancreas
Ductal obstruction and pancreatic tissue destruction
What role does CCK play in pancreatic secretion?
CCK stimulates acinar cells to increase protein secretion
It is produced by duodenal I cells in response to fatty food
What inhibits pancreatic secretion?
Somatostatin
How does somatostatin inhibit pancreatic secretion?
Inhibits the release of CCK and secretin
Name the phases of pancreatic secretion
Cephalic phase
Gastric phase
Intestinal phase
Describe the cephalic phase of pancreatic secretion
Accounts for 25%
Mediated by Ach
Describe the gastric phase of pancreatic secretion
Accounts for 10-20%
Gastrin mediated (gastrin is a weak CCK agonist)
Neural pathways via gastric distension
Describe the intestinal phase of pancreatic secretion
Accounts for 50-80%
Chyme enters the duodenum
Gastric acid triggers secretin to be produced
Lipids stimulate CCK production
How does the pancreas prevent autodigestion?
Zymogens only become activated after coming in contact with the small bowel enzyme enterokinase
Secretory granule membrane is impermeable to proteins
Enzyme inhibitors are also present in the secretory granules
pH and ionic conditions limit activity
What may cause acute pancreatitis?
Gallstones Ethanol Trauma Steroids Mumps Autoimmune Scorpion sting Hypercalcaemia ERCP Drugs
What symptoms are characteristic of acute pancreatitis?
Abdominal pain (epigastrium and radiates to the back)
Serum amylase and/or lipase >3 times the upper limit of normal
CT scan
How many stages of acute pancreatitis are there?
3
Describe phase 1 of acute pancreatitis
Premature activation of trypsin within pancreatic acinar cells
Describe phase 2 of acute pancreatitis
Intra-pancreatic inflammation
Describe phase 3 of acute pancreatitis
Extra-pancreatic inflammation
Systemic sepsis
Multiple organ failure
How is acute pancreatitis treated?
Resting the pancreas with IV fluids
Pain relief
Therapeutic Endoscopic Retrograde Cholangiopancreatography
What is chronic pancreatitis?
Chronic pancreatitis is inflammation of the pancreas that does not heal or improve
What is the most common cause of chronic pancreatitis?
Chronic alcohol abuse