Pancreatic Exocrine Secretion Physiology Flashcards
Endocrine vs exocrine glands
Endocrine glands
- ductless and secrete their products/hormones into the interstitial glands and blood system
- product is released into blood
Exocrine
- secrete product onto body surfaces through a duct
- product is released onto the surface
Two major hormones of the endocrine pancreas
Insulin
- secreted via B cells (make up 75% of entire pancreas)
- uptakes glucose from blood and stimulates formation of lipids and glycogen
- end goal = lowers glucose concentrations in blood
- **stimulated by by high blood glucose concentration/parasympathetic stimulation and high levels of AAs. Inhibited by sympathetics and somatostatin
Glucagon
- secreted by A cells (make up 10% of the pancreas)
- mobilizes lipid reserves and promotes glucose synthesis/glycogen break down in liver
- *end goal = increase glucose concentrations in blood
- **stimulated by low blood glucose, inhibited by somatostatin
Delta (D) cells
Part of the exocrine pancreas which releases somatostatin
Functions:
- inhibits insulin and glucagon secretion
- slows rates of nutrient absorption and enzyme secretion along he digestive tract
- stimulated by protein-rich meal
F cells
Secretes pancreatic polypeptide (PP)
Functions to inhibit gallbladder contractions, regulates production of pancreatic enzymes and influences rate of nutrient absorption by digestive tract.
- * stimulated by protein rich meals and parasympathetics
Exocrine pancreas secretions
Ductal cells
- bicarbonate ions
- factors that increase secretion: CCK/secretin/parasympathetics
Acinar cells
- pancreatic lipase
- amylase proteases
- factors that increase secretion: CCK/parasympathetics
Breakdown of fluid absorption and exceretion
Absorption
- small intestine 7.5L/day
- chief mover*
- large intestine 1.4L/day
Excretion
- feces 0.1L/day
How much fluid does the pancreas secrete per day?
1.5L
Pancreatic acinar cell specifics
Have high levels of rough ER and golgi due to having the highest daily rate of proteins synthesis anywhere in the body
- appear triangular/cone shaped
6 steps to secreting granules
1) rough ER ribosomes synthesizes new proteins
2) proteins are moved to Golgi apparatus
3) Golgi apparatus secrets vesicles with proteins in them
4) vesicles fuse together to form vacuoles
5) vacuoles change into zymogen granules
6) zymogen granules are secreted into the lumen
How does components of acinar cells change with respect to time after impulse?
0 minutes
- rough ER is at 100% with components
0-30 minutes
- rough ER = 30%
- golgi vesicles= 40%
- condensing vacuoles = 40%
- zymogen granules = 5%
30-60 minutes
- rough ER = 20%
- golgi vesicles = 20%
- condensing vacuoles = 30-40%
- zymogen granules = 35%
60-90 minutes
- rough ER = 20%
- golgi vesicles = 10%
- condensing vacuoles = 20%
- zymogen granules = 45%
90-120 minutes
- rough ER = 20%
- golgi vesicles = 5%
- condensing vacuoles = 10%
- zymogen granules = 55-60%
What is pancreatic secretory trypsin inhibitor (PSTI)
A 56-AA peptide that inactivates trypsin by forming a relatively stable complex with trypsin near its catalytic site
Difference between carboxypeptidase A and B with respect to function
A = cleaves terminal amino acids with aromatic and branched aliphatic side chains
B = cleaves terminal amino acids that have basic side chains
What is the function of the aqueous component of the pancreas?
Neutralization of the duodenal contents
- prevents duodenal mucosa damage from acid and pepsin by buffering the pH
How are chloride and bicarbonate related to secretion rates in pancreatic juice?
Inversely proportional
- due to bicarbonate/chloride exchanger
as secretory rate goes up, bicarbonate goes up and chloride goes dow
How are osmolality and pH related in secretion rates in pancreatic juice?
PH = directly proportional to secretory rates
Osmolality = no correlation at all
as secretory rates increase, pH increases and osmolality stays unchanged
What is the predominant mechanisms of pancreas based on neuronal stimulation?
Parasympathetics dominant
- uses ACh from vagus
Telenzepine = M1 antagonist to ACh, can be used to decrease acinar pancreatic secretion by >85%
parasympthetics increase secretion/ sympathetics decrease secretion
How does the pancreas secretion work in the presence of macromolecules
- phenylalanine, methionine, tryptophan, small peptides and FAs*
1) the above is sensed in the duodenum, which stimulates I cells to secrete CCK
2) CCK slows gastric emptying while also upregulating IP3/DAG and increasing intracellular calcium levels in acinar cells
3) all of #2 -> secretion of pancreatic enzymes
What is the effect of H+ ions on the pancreas?
1) H+ ions is sensed in the duodenum which results in S-cell stimulation -> release of secretin
2) release of secretin causes upregulation of cAMP in ductal cells of the pancreas
3) #2 results in aqueous secretion (Na+/HCO3-) from pancreatic ductal cells
What is need to potentials enzymes or aqueous secretion from the pancreas?
ACh from parasympathetics
What specific enzymes and factors initiate upregulation of IP3/DAG in pancreatic acinar cells
ACh from parasympathetics
CCK
Substance-P
Bombesin
all activate G-coupled q channels
What specific enzymes and factors initiate upregulation of cAMP in pancreatic acinar cells
Secretin and VIP
both stimulate G-coupled s channels
What is the most potent stimulator of pancreatic aqueous secretion?
Secretin
What is the most potent stimulator of pancreatic enzyme secretion?
CCK
What is potentiation?
The ability of two hormones or neuronal responses to have a synergistic
example = CCK+ VIP = more amylase secretion, Whereas CCK alone has less amylase secretion
3 phases of pancreatic secretion
1) Cephalic:
- stimulants = sight/smell/taste/mastication
- regulatory pathway = vagus
- secretes 25% of max enzymes
2) Gastric:
- stimulants = distention, levels of gastrin
- regulatory pathways = vagus
- secretes 10-20% of max enzymes
3) intestinal:
- stimulants = AA’s/FA’s/H+ ions
- regulatory pathways = CCK/secretin/Enteropancreatic reflexes
- secretes 50-80%
