FUNCTIONAL ANATOMY AND NERVE SUPPLY OF PANCREAS

FUNCTIONAL ANATOMY AND NERVE SUPPLY OF PANCREAS

Pancreas is a dual organ having two functions, namely endocrine function and exocrine function. Endocrine function is concerned with the production of hormones. The exocrine function is concerned with the secretion of digestive juice called pancreatic juice.

FUNCTIONAL ANATOMY OF EXOCRINE PART OF PANCREAS

Exocrine part of pancreas resembles salivary gland in structure. It is made up of acini or alveoli. Each acinus has a single layer of acinar cells with a lumen in the center. Acinar cells contain zymogen granules, which possess digestive enzymes. A small duct arises from lumen of each alveolus. Some of these ducts from neighboring alveoli unite to form intralobular duct. All the intralobular ducts unite

to form the main duct of pancreas called Wirsung duct. Wirsung duct joins common bile duct to form ampulla of Vater, which opens into duodenum. In some persons, an accessory duct called duct of

Santorini exists. It also opens into duodenum, proximal to the opening of ampulla of Vater.

NERVE SUPPLY TO PANCREAS

Pancreas is supplied by both sympathetic and parasympathetic fibers. Sympathetic fibers are supplied

through splanchnic nerve and parasympathetic fibers are supplied through vagus nerve.

PROPERTIES AND COMPOSITION OF PANCREATIC JUICE

PROPERTIES OF PANCREATIC JUICE

Volume : 500 to 800 mL/day

Reaction : Highly alkaline with a pH of 8 to 8.3

Specific gravity : 1.010 to 1.018

COMPOSITION OF PANCREATIC JUICE

Pancreatic juice contains 99.5% of water and 0.5% of solids. The solids are the organic and inorganic

Substances Bicarbonate content is very high in pancreatic juice. It is about 110 to 150 mEq/ L, against the plasma level of 24 mEq/L. High bicarbonate content of pancreatic juice is important because of two reasons:

 i. High bicarbonate content makes the pancreatic juice highly alkaline, so that it protects the intestinal mucosa from acid chyme by neutralizing it

ii. Bicarbonate ions provide the required pH (7 to 9) for the activation of pancreatic enzymes.

FUNCTIONS OF PANCREATIC JUICE

Pancreatic juice has digestive functions and neutralizing action.

DIGESTIVE FUNCTIONS OF PANCREATIC JUICE

Pancreatic juice plays an important role in the digestion of proteins and lipids. It also has mild digestive action on carbohydrates.

DIGESTION OF PROTEINS

Major proteolytic enzymes of pancreatic juice are try psin and chymotrypsin. Other proteolytic enzymes are carboxypeptidases, nuclease, elastase and collagenase.

1. Trypsin

Trypsin is a single polypeptide with a molecular weight of 25,000. It contains 229 amino acids. It is secreted as inactive trypsinogen, which is converted into active trypsin by enterokinase. Enterokinase is also called enteropeptidase and it is secreted by the brushbordered cells of duodenal mucus membrane. Once formed, trypsin itself activates trypsinogen by means of autocatalytic or autoactive action.

Trypsin inhibitor

Trypsinogen is activated only when it reaches the small intestine. If trypsin is activated when it is in pancreas, it may hydrolyze the pancreatic tissue proteins, resulting in pancreatic damage. But its activation in the secretory cells, acini and ducts of pancreas is prevented by an inhibitor protein called trypsin inhibitor. Any abnormality or deficiency of the trypsin inhibitor will result in unopposed trypsin activity, which damages the pancreas.

Actions of trypsin

i. Digestion of proteins: Trypsin is the most powerful proteolytic enzyme. It is an endopeptidase

and breaks the interior bonds of the protein molecules and converts proteins into proteoses

and polypeptides

ii. Curdling of milk: It converts caseinogen in the milk into casein

iii. Blood clotting: It accelerates blood clotting

iv. It activates the other enzymes of pancreatic juice, viz.

a. Chymotrypsinogen into chymotrypsin

b. Procarboxypeptidases into carboxypeptidases

c. Proelastase into elastase

d. Procolipase into colipase

v. Trypsin also activates collagenase, phospholipase A and phospholipase B

vi. Autocatalytic action: Once formed, trypsin itself converts trypsinogen into trypsin.

2. Chymotrypsin

Chymotrypsin is a polypeptide with a molecular weight of 25,700 and 246 amino acids. It is secreted as inactive chymotrypsinogen, which is activated into chymotrypsin by trypsin.

Actions of chymotrypsin

i. Digestion of proteins: Chymotrypsin is also an endopeptidase and it converts proteins into

polypeptides

ii. Digestion of milk: Chymotrypsin digests caseinogen faster than trypsin. Combination of both

enzymes causes rapid digestion of milk

iii. On blood clotting: No action.

3. Carboxypeptidases

Carboxypeptidases are carboxypeptidase A and carboxypeptidase

B. Carboxypeptidase A is derived from the precursor procarboxypeptidase A. Carboxypeptidase B

is derived from procarboxypeptidase B. Procarboxypeptidases are activated into carboxypeptidases by trypsin.

Actions of carboxypeptidases

Carboxypeptidases are exopeptidases and break the terminal bond of protein molecules. Exopeptidases split the polypeptides and other proteins into amino acids. Carboxypeptidase A splits the proteins into

amino acids having aromatic or aliphatic side chains. Carboxypeptidase B converts the proteins into amino acids having basic side chains.

4. Nucleases

Nucleases of pancreatic juice are ribonuclease and deoxyribonuclease, which are responsible for the

digestion of nucleic acids. These enzymes convert the ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) into mononucleotides.

5. Elastase

Elastase is secreted as inactive proelastase, which is activated into elastase by trypsin. Elastase digests the elastic fibers.

6. Collagenase

Collagenase is secreted as inactive procollagenase, which is activated into collagenase by trypsin. It digests collagen.

Post a Comment

0 Comments