Pancreatic Exocrine Function Flashcards
3 parts of the pancreas, main ducts
Tail, head, body
Main pancreatic duct joins with common bile duct and empties into duodenum via major duodenal papilla
3 types of cells in the pancreas
Islets of langerhans
Acinar cells
Ductal cells
Shape of the tubules and ducts in the pancreas
A compound tubuloacinar gland
Branched so that we can create a lot of protein in a small amount of space
Acinar cells
Serous acini
Protein factories so have a lot of RER and Golgi
Pathway of enzymes from production to excretion
Made at the basal side on the RER
To Golgi
To condensing vacuoles (water pumped out of the vacuoles, lots of Ca for folding)
Become zymogen granules (entirely made of proteins)
When stimulated they dock with the lumen and release via exocytosis
Enzymes are made by acinar cells to degrade what 4 things
Fats (lipases, colipase, etc)
Starch (amylase)
Protein (trypsin, chymotrypsin, etc)
DNA/RNA (deoxyribonuclease, etc)
Enzymes produced to degrade ___ and ___ are secreted in an inactive form
Fats
Protein
2 ways the pancreas prevents autodigestion
Making enzymes in their inactive form
Packaging them into zymogen granules with high pH
How does trypsin get activated?
Trypsinogen activated by enterokinase (aka enteropeptidase) into trypsin
Trypsin can then cleave itself and other proteases
Reaction proceeds via positive feedback until all enzymes are activated
Cephalic phase of pancreatic secretion
Sight, smell and taste of food cause stimulation of dorsal motor nucleus of vagus in the brain
1. Causes ACh to be released and acts on M3 receptor
2. Causes gastrin-releasing peptide to be released and act on G cells - cause gastrin to bind to CCKA cells on acinar cells
3. Release ACh and VIP to activate alkaline fluid production by ductal cells
Senses stimulate 25% of acinar cell capacity secretion levels
Gastric phase of pancreatic secretion
Food in stomach can activate the brain (and dorsal motor nucleus - same pathways as cephalic)
Peptides and amino acids in antrum can directly stimulate G cells for gastrin release (act on acinar cells)
10-20% of secretion comes from stomach stimuli
Intestinal phase of pancreatic secretion
Chyme in the duodenum activates 3 things:
1. Protein and lipid breakdown stimulates vagovagal reflex that stimulates the acinar cells (Ach on M3)
2. H+ stimulates S cells to secrete secretin (acts on ductal cells to stimulate bicarb release)
3. Protein and lipid breakdown stimulates I cells to secrete CCK (acts on acinar cells)
50-80% of secretion capacity is stimulated by food in intestine
What neutralizes the pH
- Along the brush border
- In the lumen
- Brunner’s glands
2. Pancreatic secretions (bicarb)
How does the pancreas ensure unidirectional flow?
The ductal cells at the periphery secrete more bicarb than the central ones
Ductal cells closer to the duodenum have more fluid running over them, so make more mucins
What does
1. ACh
2. Secretin
stimulate in the ductal cell
- Increase in bicarb secretion (minor role)
- Increase cAMP, activates PKA, Cl- pumped out via CFTR (creates a gradient so that HCO3 can be pulled into the cell to balance the negative charge, and then be pumped out via a Cl/HCO3 antiporter)
