Why is saliva a hypotonic solution?

Saliva is made in the acinar cells of the salivary gland. The initial secretion is isotonic with plasma. read more

A hypotonic solution is a solution that has a lower concentration of insoluble molecules (e.g. Sodium, potassium and chlorine) compared to the other side of a membrane. Saliva is hypotonic due to the fact that reabsorption of Na+ and Cl- is greater than the secretion of K+ and HCO3- within the salivary duct. read more

A hypotonic solution is a solution having a lesser solute concentration than the cytosol. It contains a lesser concentration of impermeable solutes on the external side of the membrane. In terms of saliva, it becomes more dilute compared to plasma. read more

Acinar cells secrete a isotonic mixture of saliva which then gets modified through the ductal cells to produce a hypotonic saliva compared to plasma with a high K+ and HCO3- concentration. HOWEVER, at high flow rates the saliva actually resembles plasma (isotonic) because there wasn't enough to modify the saliva. read more