Physiology-Pancreas Flashcards
What cells are contained in the region indicated below?
The lighter staining region in the pancreatic parenchyma are Islets of Langerhans, which contain the endocrine cells of the pancreas.
What is the function of the different cell types found in the region of the pancreas indicated below?
In the Islet of Langerhans you have 1) Beta Cells: interior of islet, secrete alcohol-soluble insulin granules. 2) Alpha Cells: periphery of islet, secrete alcohol-insoluble glucagon granules. 3) Delta cells: paracrine secretion of somatostatin. 4) F (or PP) cells: make pancreatic polypeptide.
What structures are found in the interlobular connective tissue of the pancreas?
Large excretory ducts, blood vessels and nerves.
What kind of capillaries run through the Islets of Langerhans?
Fenestrated capillaries
How does the pancreatic acinus differ from that in the submandibular gland?
No striated ducts in the pancreas, only serous cells in pancreas, no myoepithelial cells in the pancreas, and centroacinar cells mark the beginning of the intercalated ducts in the pancreas.
Where are the granules located on the exocrine cells of the pancreas?
Zymogen granules are located on the apical side of the cells
Identify the different structures labeled below.
1) Pancreatic acinus, note eosinophilic at base b/c nucleus is on basal side of cell and granules are at apical side 2) Intercalated duct 3) Centroacinar cell
What role do centroacinar cells play in pancreatic secretions?
They express high levels of carbonic anhydrase and play a role in secretion of bicarbonate.
What cells are critical in determining the ionic composition of the fluid that leaves the pancreas?
Intercalated duct epithelium. They are the main secreters of fluid in the pancreas.
Proteolytic enzymes secreted by the pancreas
Endopeptidases (Trypsinogen, chymotrypsinogen, proelastase) and exopeptidases (procarboxypeptidase A/B, proaminopeptidase)
Nucleolytic enzymes secreted by the pancreas
Ribonuclease and deoxyribonuclease
Lipolytic enzymes secreted by the pancreas
Procolipase, lipase, prophospholipase A2 and carboxyl ester hydrolase
Amylolytic enzyme secreted by the pancreas
Alpha-amylase
In addition to secretion of hydrolytic enzymes, what else do acinar cells produce to protect the pancreas?
Trypsin inhibitor. It prevents the conversion of trypsinogen to trypsin before secretions reach the duodenum.
What triggers secretion of hydrolytic enzymes from the acinar cells?
CCK and ACh -> PKC signaling.
What triggers secretion of Na, K, HCO3 and Cl from the acinar cells? From the interlobular ducts?
Acinar cells = spontaneous. Interlobular ducts = secretin or VIP -> cAMP signaling, note that these secretions are more rich in bicarbonate.
What happens to fluid Cl levels are secretory rate increases?
It decreases. HCO3 is let out and HCO3 concentration increases by taking Cl back into the cell via the CFTR.
What cells secrete secretin?
Enteroendocrine (S) cells when the chyme enters the small intestine.
Where do duct cells get all that bicarb from?
CO2 + H2O + Carbonic anhydrase. Na/HCO3 basal cotransporter.
Where does VIP come from?
Vasoactive intestinal peptide is a hormone release by the vagus nerve.
What cells secrete CCK?
Enteroendocrine (I) cells when the fatty acids and peptides in the chyme enter the small intestine
How does sympathetic stimulation affect pancreatic secretions?
Inhibits vagal and secretion induced secretions.
4 phases of pancreatic secretion
1) Resting phase: vagal stimulation -> ACh (zymogen release) and VIP (fluid release) 3) Gastric phase: stomach distention -> vagal stimulation and gastrin release -> additional secretion of alkaline fluid 4) Intestinal phase: chyme enters duodenum -> secretin release -> 70-80% of pancreatic secretion into duodenum occurs
What do activated proteases in the duodenum do besides break down food?
Inhibit acinar cell zymogen release
What substance suppresses vagal stimulation of acinar cell zymogen release?
Pancreatic polypeptide (PP)
What hormone is released in presence of fat in lower intestine that also inhibits pancreatic secretions?
NPY
What hormones are present after food has been absorbed into circulation that inhibit pancreatic secretions?
Glucagon, somatostatin and PP
Why does pancreatic fluid need to be alkaline?
Hydrolytic enzymes are only activated at higher pH
Common causes of acute pancreatitis?
Alcohol or blockage of common bile duct. Consquence is pancreatic enzymes digestion pancreatic tissue.
Pancreatitis without pain.
Cystic fibrosis, pancreatitis due to decreased HCO3 secretion from loss of CFTR.
