Exocrine Pancreas Flashcards
The pancreas is _____
Bi-lobed
- body: pylorus
- right lobe: mesoduodenum, ventral to right kidney, apposition to duodenum
- left lobe: caudal to stomach and liver
Exocrine functions of pancreas
- enzymes secreted into a duct
- ducts lead to external environment
- digestive enzymes
Endocrine functions of pancreas
- hormones secreted into the blood
- function at distant sites, not on the cells that secreted them
- insulin
Exocrine histologic anatomy
- acini: digestive enzymes
- ducts: bicarbonate
Endocrine histologic anatomy
Islets of Langerhans
- alpha cells: glucagon
- beta cells: insulin
- delta cells: somatostatin/gastrin
- PP cell: pancreatic polypeptide
Acini are arranged as a ______
Cluster of grapes
- lead out to the pancreatic or accessory duct
- bicarb is made within the ducts
Sympathetic innervation
Inhibitory!!!
- celiac plexus
- mesenteric plexus
Parasympathetic innervation
Stimulatory!!
- branches of vagus or other cholinergic nerves in the enteric nervous system
- terminate in acini (exocrine) or islets (endocrine)
In dogs, the bile duct enters _______
Major duodenal papilla
Accessory pancreatic duct (dogs)
Most important
- enters minor duodenal papilla
- separate from bile duct
Pancreatic duct (dogs)
Less important
- may not be present
- empties into major duodenal papilla separate from bile duct
Most pancreatic secretions in the dog go into the _______
Accessory pancreatic duct
Pancreatic duct (cats)
Most important
- enters major duodenal papilla –> after joining with the common bile duct first
Accessory pancreatic duct (cats)
Only present in 20% of cats
Triaditis
Common in cats
- inflammation affects the liver, common bile duct, and the gallbladder = back up of bile flow
- pancreatitis can make cats yellow, liver complications are secondary
What are the 3 functions of the exocrine pancreas?
- release of mostly inactive digestive enzymes
- neutralization of gastric acid
- secretion of intrinsic factor
Intrinsic factor
Secreted by parietal cells in humans
- facilitates B12 absorption in the distal small intestine
Lack of B12
Pernicious anemia in people
- diarrhea in dogs and cats
Bicarbonate secretion
Released by ductal cells
- neutralizes gastric acid
- intestinal mucosa protection
- increased pH necessary for enzyme activity
- reaches 5 times the plasma bicarb concentration
Enzymes are only functional at a _______
Higher pH
What are the 3 functions of pancreatic enzymes?
- protein digestion
- carbohydrate digestion
- fat digestion
Protein digestion
Zymogens
- trypsinogen
- chymotrypsinogen
- procarboxypeptidase
Carbohydrate digestion
Pancreatic amylase
Fat digestion
- pancreatic amylase
- cholesterol esterase
- phospholipase
Proteolytic enzymes following activation
- trypsin
- chymotrypsin: both split whole proteins or partially-digested peptides into smaller peptides
- carboxypeptidase: splits some peptides into individual amino acids
Pancreatic amylase
Hydrolyzes starches
- glycogen and others
- into di- or trisaccharides
Pancreatic lipase
Neutral fat –> FA + monoglycerides
- cholesterol esterase: hydrolysis of cholesterol esters
- phospholipase: separates FAs from phospholipids
Protection from auto-digestion
- zymogen synthesis (proteases)
- segregation into vacuoles in acinar cell (separate from lysosomes)
- trypsin inhibitors in cytoplasm (and some are circulating)
- sphincter at pancreatic duct (inhibits reflux)
Zymogen
Prozymes (inactive enzyme)
- trypsinogen
- chymotrypsinogen
- activation required
Zymogens are synthesized by _______
Ribosomes
- formation and storage in vesicles
Zymogen stimulation of the cell
Fusion of granules to plasma membrane –> release of content into glandular lumen –> secretion into duodenum
Zymogens are activated in the ______
Duodenum
- enterokinase (brush border enzyme) –> activates trypsinogen into trypsin
Trypsin activates
- trypsinogen
- chymotrypsinogen
- others
Trypsin inhibitors
Prevents activation of trypsin
- formed and stored in acinar cytoplasm
- secreted by acinar cells (acini, ducts)
- alpha-2 macroglobulin –> helps remove proteases from plasma, tags digestive enyzmes for removal
Alpha-2 macroglobulin is synthesized in the
Liver
Pancreatic lipase immunoreactivity
Increased = pancreatitis
- enzymes are unchecked
- activation in pancreas
- released into the bloodstream
Vasoactive intestinal polypeptide/peptide
Enteric neurotransmitter released by vagal neurons
- stimulates ductal cells to secrete bicarb-rich fluid
- inhibitory to rest of GIT = relaxation of sphincters and descending relaxation in the intestine
Secretin
Hormone released by duodenal S cells
- response to acidification
- similar effect on ductal cells as VIP
- stimulates bicarb from liver
Acetylcholine
Released by postganglionic vagal neurons on or near acinar cells
- neurocrine stimulation
CCK
Cholecystokinin
- released by duodenal and jejunal cells into bloodstream to act as an endocrine hormone
- secreted in response to AAs, FAs, and HCl
Gastrin
In dogs:
- released by antral G cells into bloodstream, where it circulates to acinar cell
- endocrine stimulation
______ and _____ stimulates pancreatic enzyme secretion in the guinea pig, but not dog/cat
Secretin and VIP
Cephalic phase
Smelling, tasting, chewing
- minor (20%)
Gastric phase
When food enters the stomach
- gastric distention
Intestinal phase
Most important phase!!
- begins when food hits the small intestine
The cephalic phase of pancreatic secretions has ________
Neuronal regulation
- vagus stimulates parietal cell H secretion –> duodenal secretin release = pancreatic fluid and bicarb secretion
- vagus stimulates gastrin from antral G cells –> pancreatic enzyme secretion (dogs) –> also stimulates parietal cells to secreted H = secretin secretion
If a dog has pancreatitis, it may be painful for him to
Smell food
In the gastric phase of pancreatic secretion, protein digestion products stimulate
Gastrin release
- HCl from parietal cell (secretin release) and pancreatic enzymes (dog)
Gastric distension simulates the
Vagal reflex
- HCl release from parietal cells –> secretin secretion from S cells
Distension from food hitting the stomach causes
Vagal stimulation –> release of Ach and enzymes –> VIP and bicarb secretion
Intestinal phase of pancreatic secretion results in
- fats, peptides –> CCK release from I cells = enzymes
- decrease pH –> secretin release from S cells = bicarb secretion
- large volume of fluid
