Transcript it will be released when the PH of duodenal content fall below 4.5

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.
• 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.
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.
• 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 .
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
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
.
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
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
,
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