Explain the Role of secretin

Secretin is a polypeptide containing 27 amino acids. It is present in the mucosa of the upper small intestine in an inactive form prosecretin. When food mixed with hydrochloric acid enters the duodenum, secretin is released from prosecretin. Secretin causes the pancreas to secrete large quantities of fluid containing a high concentration of bicarbonate ion. This copious flow of fluid is called hydrelatic secretion because it is mainly a thin watery solution containing almost no enzymes. Pancreatic juice containing large quantity of sodium bicarbonate is helpful to neutralize the acid content of substances emptied into the duodenum from the stomach. The reaction is as follows:

Carbonic acid dissociates into water and carbon dioxide. Carbon dioxide is absorbed into the body fluids. A neutral solution of sodium chloride is left. Bicarbonate secretion also provides an appropriate pH for the action of pancreatic enzymes.