Pancreatic secretion:

1. Pancreatic secretion: In addition to secreting insulin by the islet cell of langerhans . Digestive enzymes are secreted by pancreatic acini, &large volume of sodium bicarbonate secreted by ductules & ducts. Secretion of pancreatic enzymes: Pancreatic secretion contains enzymes for digesting all 3 types of food, also it contain large quantity of HCO3which plays important role in neutralizing acid chyme.

2. The most important proteolytic enzymes are trypsin, chymotrypsin& carboxypolypeptidase , the most abundent of these is trypsin, the trypsin &chymotrypsin split whole&partially digested proteins into peptides but not cause the release of indivisual amino acids, carboxypolypeptidase split some peptides into indivisual amino acids. • The panreatic enzymes for digestion of carbohydrates is amylase which hydrolyse starch. • The main enzyme for fat digestion are lipase , cholesterole esterase&phospholipase.

3. When synthesized in panreatic cell, proteolytic enzymes are in inactive form , they become activated only after they are secreted into the intestinal tract, trypsinogen (inactive form of trypsin) activated by enterokinase secreted by intestinal mucosa when the chyme come in contact with mucosa , trypsin is key for activation of chymotrypsinogen & procarboxypolypeptidase.

4. its important that pancreatic enzymes are in inactive form in the pancrease, because they digest the panrease itself ,, the same cell which secret the pancreatic enzymes secrete another substance called trypsin inhibitors , it stored in the cytoplasm of glandular cells that surround the enzyme granules, it prevent activation of trypsin in the secretory cells & in acini&ducts, because trypsin activate other enzymes , , the inhibitors prevent the subsequant activation of others as well .

5. Secretion of bicarbonate ions & water : they are secreted in large quantity mainly by the epithelial cells of the ductules & ducts that lead from the acini . . When the pancreas is stimulated to secrete copious quantities of pancreatic juice, the bicarbonate ion concentration can rise to as high as 145 mEq/liter a value about 5 times that of bicarbonate ions in the plasma . This provides a large quantity of alkali in the pancreatic juice that serves to neutralize acid emptied into the duodenum from the stomach

6. The mechanism for secretion of HCO3 in pancreatic ductules &ducts is: 1- H2O combined with CO2 to form carbonic acid which dissociated into H+& HCO3 , Hco3 actively transported in exchange with CL-, H+ also actively transported in exchange with Na+, the movement of Na+&Hco3 from blood to the lumen of duct create osmotic gradient that cause osmosis of water into the duct .

7. Regulation of pancreatic secretion : Basic stimuli of pancreatic secretion : 1- Ach 2- cholecystokinn 3- secretin The 1st 2 stimulate the acini to secret digestive enzyme , where as the 3rd stimulate the secretion of sodium bicarbonate by the ducts . Phases of pancreatic secretion: 1- cephalic & gastric phase :same signals that cause secretion in stomach , cause the release of Ach from the vagal nerve ending in pancrease 2- intestinal phase : after chyme enters the S.I pancreatic secretion become copious in response to hormone, cholycystokinine cause still much more secretion of enzyme.

8. Role of secretin: When an acid chyme with pH less than 4.5 - 5 enter duodenum , it cause release& activation of secretin ( a poly peptide present in mucosa of upper S.I) subsequantly it will be absorbed into the blood, it inturn cause the pancrease to secrete large quantity of fluid contain high concentration of bicarbonate ion . Secretin mechanism is important because: it will be released when the PH of duodenal content fall below 4.5 – 5 &its release is increase greatly as the PH fall to 3, this immediately causes copious amounts of pancreatic juice containing abundant amount of NaHco3 to be secreted which result in Hcl+ NaHCO3 → Nacl + H2co3 H2co3 dissociated immediately into H2o &CO2 which absorbed in to the blood &expired by the lungs ,thus leaving neutral solution of sodium chloride in the dudenum ,

9. Cholecystokinin (controle of secretion of enzyme by pancrease): Prescence of food in the upper S.I cause cholecystokinin to be released from mucosa of upper S.I., carried by the blood to the pancrease cause the release of digestive enzyme( account 70 -80% of pancreatic secretion