Functions of Pancreatic Juice

• A digestive juice secreted by pancreas and is the exocrine function of it.
• Endocrine function is related with secretion of hormones.
• Has neutralizing action on acidic food coming from gastric region.
• The various functions are:

A) Digestive functions

• Important role played in digestion of proteins and lipids.
• Carbohydrates are also acted upon mildly by this juice.

B) Digestion of proteins

• Trypsin and chymotrypsin acts as major enzymes of pancreatic juice.
• Are generally major proteolytic enzymes.
• Carboxypeptidases, nucleases, elastase and collagenase are the minor ones.

a) Trypsin

• Made up of 229 amino-acids.
• A single polypeptide having molecular weight of 25,000.
• Trypsinogen is the inactive form of it at secretion time.
• Enterokinase also called enteropeptidase acts on it and give an active form trypsin.
• Brush bordered cells of duodenal mucus membrane secretes enterokinase.
• Once the trypsin is formed, left trypsinogen are activated by it.
• Activation is done by autocataytic or autoactive action.

Trypsin inhibitor

• Activation of trypsinogen occurs only when it reaches small intestine.
• Trypsin if activated in pancreas, before reaching small intestine, can hydrolyze the pancreatic tissue proteins.
• This can cause damage of the pancreas.
• Trypsin inhibitor, an inhibitor protein plays vital role in it.
• It blocks trypsin activation in the secretory cells, acini and ducts of pancreas.
• Abnormality or deficiency condition of trypsin inhibitor hence cannot oppose trypsin activity.
• Thus, pancreas gets damaged in its abnormal or deficiency condition.

Actions of Trypsin

i) Digestion of proteins

• One of the most powerful proteolytic enzymes which is an endopeptidase.
• Due to this, protein molecules having interior bonds are broken.
• Thus, proteins are converted to proteoses and polypeptides.

 Image source: pathwayz

ii) Conversion of caseinogen in the milk into casein resulting in curdling of milk.

iii) Accelerated clotting of blood.

iv) Activates other enzymes of pancreatic juice

• Inactive chymotrypsinogen to active chymotrypsin
• Procarboxypeptidases to carboxypeptidases
• Proelastase to elastase
• Procolipase to colipase.

v) Activation of collagenase, phospholipase A, phospholipase B

vi) Shows autocatalytic function that means once formed converts trypsinogen to trypsin.

b) Chymotrypsin

• Made up of 246 amino acids.
• Also a polypeptide having molecular weight 25,700.
• Secretion occurs in inactive form chymotrypsinogen.
• Activated form is chymotrypsin done by trypsin.

Actions of Chymotrypsin

i) Digestion of proteins

• Also an endopeptidase.
• Converts proteins to polypeptides.

ii) Digestion of milk

• Caseinogen in milk is digested faster by it than trypsin.
• Rapid digestion occurs in their combined activity.

iii) No action on blood clotting

 Image source: totalorganic

c) Carboxypeptidases

• Exists as carboxypeptidase A and B.
• Precursor procarboxypeptidase A gives rise to carboxypeptidase A.
• Likewise, for carboxypeptidase B precursor is procarboxypeptidase B.
• Trypsin activates this precursor form to active form carboxypeptidases.

Actions of Carboxypeptidases

i) Are exopeptidases.

ii) Protein molecules terminal bonds are broken by it.

iii) The polypeptides and other proteins in presence of these exopeptidases, split into amino acids.

iv) Aromatic or aliphatic side chains having amino acids are resulted by activity of carboxypeptidase A.

v) Whereas, basic side chains having amino acids are formed by carboxypeptidase B.

 

d) Nucleases

• Ribonulcease and deoxyribonuclease falls under this group.
• Responsible for digestion of nucleic acids.
• Mononucleotides are formed from RNA and DNA.

e) Elastase

• Proelastase is the form in which it is secreted.
• It is the inactive form.
• Trypsin activates it to elastase form.
• Responsible for digestion of elastic fibers.

f) Collagenase

• Secreted as procollagenase.
• Trypsin activates it to form collagenase.
• Responsible for digestion of collagen.

C) Digestion of Lipids

• Various lipolytic enzymes of pancreatic juice digest the lipid content of food.
• Lipase, cholesterol ester hydrolase, phospholipase A, phospholipase B, collipase and bile salt activated lipase are the major ones.

a) Pancreatic Lipase

• One of the powerful lipolytic enzymes.
• Triglycerides are digested to monoglycerides and fatty acids.
• Bile accelerates the activity of this enzyme.
• pH condition of 7-9 is required.
• Two more factors are required for digestion of fat.

1. Bile salts that emulsifies the fat prior to their digestion.
2. Colipase, a coenzyme is required for digesting dietary lipids.

• Maximum content of fat (80%) is digested by lipase.
• Absence or deficiency of this enzyme causes steatorrhea.
• Steatorrhea is the release of undigested fat in fecal materials.

 

b) Cholesterol ester hydrolase

• Also called cholesterol esterase.
• Converts cholesterol ester into fatty-acid and free cholesterol.
• This occurs by process called hydrolysis.

c) Phospholipase A

• Trypsin activates this enzyme.
• Lecithin and cephalin are mostly acted phospholipids.
• Thus, converted to lysophospholipids.
• Lecithin converted to lysolecithin whereas cephalin to lysocephalin.

d) Phospholipase B

• Trypsin also activates this form of phospholipase.
• Converts lysolecithin and lysocephalin to phosphoryl choline and free fatty acids.

e) Colipase

• Secreted as procolipase, an inactive form.
• A small co-enzyme.
• Trypsin activates this inactive form to colipase.
• Facilitates the digestion of fat by pancreatic lipase.

f) Bile-salt-activated lipase

• Bile salt activates this lipolytic enzyme.
• Also called cholesterol esterase or carboxyl ester lipase.
• Weaker action than pancreatic lipase.
• Hydrolyses variety of lipids like phospholipids, cholesterol esters and triglycerides.
• Human milk has similar enzyme like bile-salt-activated enzyme.

D) Digestion of Carbohydrates

• Pancreatic juice contains pancreatic amylase, an amylolytic enzyme.
• Similar in activity like salivary amylase.
• Converts starch to dextrins and maltose.

E) Neutralizing action

• When chyme enters from stomach to small intestine, large amount of pancreatic juice is also secreted.
• Large quantity of bicarbonate is present in this secretion.
• Presence of bicarbonate ions creates alkaline environment.
• That means make pancreatic juice alkaline.
• Chyme is acidic in nature and comes in contact with alkaline pancreatic juice.
• Thus, acidic chyme gets neutralized by alkaline juice.
• This neutralizing action has important role as it protects the intestine from the damage of acidic content.

References:

i) https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/pancreatic-juice

ii) https://www.healthline.com/health/what-does-the-pancreas-do#pancreas-health

Functions of Pancreatic Juice