Fig. 1. The acinar and ductal segments of secretory glands and fluid and electrolyte secretory functions.

The figure illustrates the relationships between the acinar and ductal portion of secretory glands. The acini secrete isotonic fluid with NaCl as the major salt. The fluid passes through the centroacinar cells to the duct. The pancreatic duct absorbs the Cl⁻ and secretes HCO₃⁻ and most of the water in the pancreatic juice. Active HCO₃⁻ secretion drives fluid secretion. The salivary duct absorbs both the Cl⁻ and the Na⁺ and secretes HCO₃⁻ and K⁺. ENaC is expressed in the salivary glands, but not in the pancreatic duct, and is the main pathway for Na⁺ absorption by the salivary glands duct.