Major Components of Pancreatic Juice Flashcards
Pancreas Composed of ?
- acinar cells (85% of the gland)
- and islet cells (2%)
Exocrine For ?
Digestion
Acinar Cells Funtion
- Acinar cells synthesize many enzymes
» trypsin, chymotrypsin, carboxypeptidase, and elastase
InActive Form
How to Activate Them ?
> > The duodenal mucosa expresses enterokinase on its brush boarder, which catalyzes the enzymatic activation of trypsin from trypsinogen.
> > Trypsin also plays an important role in protein digestion by propagating pancreatic enzyme activation through autoactivation of trypsinogen and other proenzymes
Amylase and Lipase ?
> > acinar cells also produce pancreatic amylase and lipase, also known as glycerol ester hydrolase, as active enzymes.
> > With the exception of cellulose, pancreatic amylase hydrolyzes major polysaccharides into small oligosaccharides, which can be further digested by the oligosaccharidases present in the duodenal and jejunal epithelium.
> > Pancreatic lipase hydrolyzes ingested fats into free fatty acids and 2-monoglycerides.
What stabilize the activity of pancreatic lipase
The main function of colipase is to stabilize the activity of pancreatic lipase in the presence of bile salts.
What protect acinar cells from autodigestion
> > acinar cells synthesize pancreatic secretory trypsin inhibitor, which also protects acinar cells from autodigestion
(SPINK1) gene function ?
> > Pancreatic secretory trypsin inhibitor is encoded by serine protease inhibitor Kazal type 1 (SPINK1) gene.
> > SPINK1 gene mutations are associated with the development of chronic pancreatitis, especially in childhood.
mutations in the CFTR gene ??
mutations in the CFTR gene have been linked to chronic pancreatitis.
This may correlate with the inability of patients with cystic fibrosis to secrete water and bicarbonate.
What is the major stimulator of the HCO3 − secretion
Secretin hormone is the major stimulator of the HCO3 − secretion
Function HCO3
> > Once the HCO3 − secreted by pancreatic duct cells reaches the duodenal lumen, it neutralizes the hydrochloric acid secreted by gastric parietal cells.
> > Pancreatic enzymes are inactivated at a low pH; therefore, pancreatic bicarbonate provides an optimal pH for pancreatic enzyme function.
The optimal pH for chymotrypsin and trypsin , Amylase and Lipase
> > The optimal pH for the function of chymotrypsin and trypsin is 8.0 to 9.0
> > for amylase, the optimal pH is 7.0
> > for lipase, it is 7.0 to 9.0.
Phases and Regulation of Pancreatic Secretion
The first phase is the cephalic phase, in which the pancreas is stimulated by the vagus nerve in response to the sight, smell, or taste of food.
This phase is generally mediated by the release of acetylcholine at the terminal endings of postganglionic fibers.
The main effect of acetylcholine is to induce acinar cell secretion
20% to 25% of the daily secretion of pancreatic juice.
The second phase of pancreatic secretion is known as the gastric phase
> > mediated by vagovagal reflexes triggered by gastric distention after the ingestion of food.
> > These reflexes induce acinar cell secretion.
> > It accounts for 10% of the pancreatic juice produced daily.
The most important phase of pancreatic secretion is the intestinal phase
- accounts for 65% to 70% of the total secretion of pancreatic juice.
- It is mediated by secretin and CCK.
- Acidification of the duodenal lumen induces the release of secretin by S cells.
- It is the most important mediator of the secretion of water, bicarbonate, and other electrolytes into the duodenum.
Secretin Vs CCK
> > The presence of lipid, protein, and carbohydrates inside the duodenum induces the secretion of CCK-releasing factor and monitor peptide.
> > Both peptides induce release of CCK by I cells present in the duodenal mucosa.
> > Whereas secretin is the main mediator of the secretion of water and bicarbonate in the intestinal phase
> > CCK is the main mediator of the secretion of pancreatic enzymes.
CCK Effect
- CCK travels through the bloodstream and induces the release of pancreatic enzymes by acinar cells.
- CCK induces local duodenal vagovagal reflexes that cause the release of acetylcholine, vasoactive intestinal peptide, and gastrin-releasing peptide, which promotes the release of pancreatic enzymes.
- CCK induces the relaxation of the sphincter of Oddi. Also, CCK potentiates the effects of secretin, and vice versa.
