Lecture handsout

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By: Dr. Anju Jha
Assistant Professor

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The pancreatic juice contains enzymes
that are of major importance in digestion.
Pancreas is a large compound gland.
Most of its internal structure is similar to
that of the salivary glands.
Its secretion is controlled in part:
 by a reflex mechanism
 by the GI hormones secretin and
cholecystokinin (CCK).

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Sr. no. Substances
1 Cations - Na+, K+, Ca++, Mg++
2 Anions- HCO3-, Cl-, SO4-- , HPO4-
3. Digestive enzymes
(95% of proteins in pancreatic
juice)
4. Other proteins.

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Multiple enzymes for digesting all of the
three major types of food:
 proteins,
 carbohydrates,
 fats.
For digesting proteins are:-
 trypsin,
 chymotrypsin,
 carboxypolypeptidase.
 For digesting carbohydrates :-
 Pancreatic amylase - hydrolyzes starches,
glycogen, and most other carbohydrates
 The main enzymes for fat digestion
 Pancreatic lipase – hydrolyzes neutral fat
into fatty acids and monoglycerides.
 Cholesterol esterase - hydrolysis of
cholesterol esters.
 Phospholipase - splits fatty acids from
phospholipids.

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The pancreatic juice is alkaline and has a
high HCO3− content.
Approximately 113 mEq/L vs 24 mEq/L in
plasma.
Presence of chyme in the upper portions
of the small intestine stimulates
pancreatic secretion.
Characteristics of the pancreatic juice
depends on the types of food in the
chyme.
The proteolytic enzymes of the
pancreatic juice activated only after they
have been secreted into the intestine.
The cells secreting proteolytic enzymes
simultaneously secrete another
substance called trypsin inhibitor.
Trypsin inhibitor prevents activation of
the other enzymes as well.

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 Other two important components of
pancreatic juice are HCO3- ions and water.
 Secreted mainly by the epithelial cells of
the ductules and ducts that lead from the
acini.
 When pancreas secretes copious quantities
of pancreatic juice:-
 the bicarbonate ion concentration can rise
to as high as 145 mEq/L,
 It is about five times that of bicarbonate
ions in the plasma.

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Basic Stimuli That Cause Pancreatic
Secretion
 Acetylcholine.
 Cholecystokinin - by the duodenal and
upper jejunal mucosa.
 Secretin - by the duodenal and jejunal
mucosa when highly acidic food enters
the small intestine.
Acetylcholine and cholecystokinin -
pancreatic digestive enzymes
Most of the enzymes remain temporarily
stored in the acini and ducts.
Fluid secretion needed to wash them into
the duodenum.

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 Secretin stimulates secretion of
large quantities of water solution of sodium
bicarbonate by the pancreatic ductal
epithelium.
 Cephalic Phase - 20% of pancreatic
secretion.
 Gastric Phase – 5-10% of pancreatic
secretion.
 Intestinal phase – rest of pancreatic
secretion.

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Entero pancreatic reflex?
In the wall of the first few centimeters of
the duodenum compound mucous glands
are present.
These are Brunner’s glands.
Location of Brunner’s glands :-
Mainly between the pylorus of the
stomach and the papilla of Vater.

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 These glands secrete large amounts of
alkaline mucus
 Stimulus for secretion :
 Tactile or irritating stimuli on the duodenal
mucosa;
 Vagal stimulation,
 GI hormones, especially secretin
 The function of secretion of Brunner’s
glands is to protect the duodenal wall from
digestion by the highly acidic gastric juice
emptying from the stomach.

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 Located over the entire surface of the small intestine
are small pits called crypts of Lieberkühn.
 These crypts lie between the intestinal villi.
 The surfaces of both the crypts and the villi are
covered by an epithelium composed of two types of
cells:
 Goblet cells - secrete mucus that lubricates and
protects the intestinal surfaces,
 Enterocytes –
 Secrete large quantities of water and electrolytes in
the crypt .
 On the surfaces of adjacent villi- which help to
reabsorb the water and electrolytes along with the
end products of digestion.

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 The intestinal secretions are formed at a
rate of about 1800 ml/day.
 Alkaline pH in the range of 7.5 to 8.0.
 Enterocytes of the mucosa, especially those
that cover the villi, contain digestive
enzymes.
 These digestive enzymes digest specific
food substances while they are being
absorbed through the epithelium.
 Succus entericus.
Intestinal enzymes are the following:
 Peptidases for splitting small peptides into
amino acids.
 Four enzymes—sucrase, maltase, isomaltase,
and lactase — for splitting disaccharides
into monosaccharides.
 Intestinal lipase for splitting neutral fats into
glycerol and fatty acids.

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 Liver secretes bile, normally between 600
and 1000 ml/day.
 Bile serves two important functions:-
 1st Important role in fat digestion and
absorption.
 2nd Excretion of several important waste
products from the blood.
 The waste products include in particular
bilirubin.
 It is end product of hemoglobin
destruction and excesses of cholesterol.
 Bile is made up of the
 bile acids
 bile pigments,
 other substances dissolved in an alkaline
electrolyte solution.
 Enterohepatic circulation
 Bile acids that represent the most important
components.
 Bile acids synthesized from cholesterol.
 These are secreted into the bile conjugated to
glycine or taurine,a derivative of cysteine.

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Bile is secreted in two stages by the liver:
Initial portion - secreted by hepatocytes.
Initial portion contains
 large amounts of bile acids,
 cholesterol
 other organic constituents.
It is secreted into minute bile canaliculi
that originate between the hepatic cells.

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Hepatocytes
Bile canaliculi
Inter lobular duct
Terminal bile duct
Hepatic duct
Common bile duct
DuodenumCystic duct
Gall Bladder
 2nd portion of liver secretion
 While passing through the bile ducts a watery
solution of sodium and bicarbonate ions
secreted by epithelial cells that line the ductules
and ducts.
 2nd secretion sometimes increases the total
quantity of bile by as much as 100%.
 2nd secretion is stimulated especially by secretin.
 Stimulation leads to release of additional
quantities of bicarbonate ions to supplement the
bicarbonate ions in pancreatic secretion.

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 The maximum volume that the gallbladder
can hold is only 30 to 60 milliliters.
 Water, sodium, chloride, and most other
small electrolytes are continually absorbed
through the gallbladder mucosa.
 12 hours of bile secretion (about 450 ml)
can be stored in the gallbladder.
 Most of this gallbladder absorption is
caused by active transport of sodium
through the gallbladder epithelium.
 Gall bladder emptying - by rhythmical
contractions of the gallbladder wall.
 Effective emptying also requires simultaneous
relaxation of the sphincter of Oddi.
 The most potent stimulus for causing the
gallbladder contractions is the hormone CCK.
 The stimulus for CCK is mainly the presence of
fatty foods in the duodenum.
 Gallbladder is also stimulated less strongly by
acetylcholine-secreting nerve fibers from both
the vagi and the intestinal enteric nervous
system.

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Fat emulsification.
Acute pancreatitis.
Lactase deficiency.
Cholelithiasis
Cholangitis

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