In an animal experiment, the pancreatic duct is cannulated and different secretory stimuli are applied to the gland. The following tracings are obtained by measuring pancreatic fluid constituents: Substance 'X' is most likely which of the following?

Question

In an animal experiment, the pancreatic duct is cannulated and different secretory stimuli are applied to the gland.  The following tracings are obtained by measuring pancreatic fluid constituents:  Substance 'X' is most likely which of the following?

Quizplus · Accepted Answer

Secretin is a hormone produced by duodenal S-cells and released in response to increased duodenal H⁺ concentrations. Secretin stimulates pancreatic ductal cells to increase bicarbonate secretion in order to neutralize the acidity of the gastric contents entering the duodenum. Remember that pancreatic juice is an isotonic secretion, which normally contains Na⁺ and K⁺ in the same concentrations as found in plasma, a higher HCO3^- concentration than in plasma and a lower Cl^- concentration than in plasma. As pancreatic juice flow rates and secretin stimulation increase, the concentration of HCO₃^- increases and the concentration of Cl^- decreases. (Choice A) Regardless of flow rate or hormonal stimulation, the sodium concentration of pancreatic secretions is identical to that of plasma. (Choice B) The chloride content of pancreatic secretions decreases as the bicarbonate content increases, because chloride and bicarbonate are exchanged for one another at the apical surfaces of pancreatic ductal cells. (Choice C) Trypsinogen is a pancreatic proenzyme that is converted to its active form, trypsin, by enterokinase in the intestinal brush border. Active trypsin can also activate trypsinogen. Cholecystokinin and cholinergic stimulation increase the secretion of pancreatic enzymes. (Choice E) Phosphate secretion is not regulated in the pancreas. Educational Objective: Duodenal S-cells secrete secretin in response to increasing H⁺ concentrations. Secretin increases pancreatic bicarbonate secretion. The chloride content of pancreatic secretions decreases in proportion to bicarbonate concentration increases.

In an Animal Experiment, the Pancreatic Duct Is Cannulated and Different