THE ROLE OF THE SALIVARY DUCT SYSTEM IN THE FORMATION OF THE SALIVA

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Abstract
A method is described for testing whether the saliva changes in composition as it passes down the secretory ducts. The use of radioactive potassium, sodium, and urea shows an exchange of these materials with the blood after secretion by the acini. Analysis of the relationships between specific activity of the isotope in the saliva and venous blood leads to the conclusion that the exchange is occurring between the saliva in the ducts and blood flowing in a capillary system surrounding the ducts. In these capillaries the blood is flowing in a direction counter to that of the saliva. A mathematical analysis of the behavior of urea in the ducts has been made. A theory of salivary secretion is presented in which the primary secretory event is the extrusion of potassium and accompanying anions into the acini. Water follows the ions passively. In the ducts the potassium is reabsorbed and only partly replaced by sodium ions diffusing in from the plasma. The potassium is recycled to the acini by the tubule portal system.