pH and Bicarbonate Concentration 145 



It needs to be emphasized that saliva secreted at a reasonable 

 rate and perhaps also resting saliva rapidly becomes alkaline in the 

 mouth due to the loss of dissolved C0 2 . 



Bicarbonate is present in the submaxillary and parotid saliva in 

 a concentration higher than that in the serum when the rate of 

 saliva secretion is above about 10-20 per cent of the maximum rate 

 (Fig. 8.4). At lower rates of secretion, bicarbonate concentrations 

 as low as 5-10 mEq/1. may be found. With increased saliva flow 

 rate the bicarbonate concentration rises and eventually stabilizes 

 at a level which is not changed by further increase in saliva flow 



Plasma 



Na (143.3) 



1.0 2.0 3 4.0 



Flow of saliva in ml./min 



Fig. 8.4. Schematic diagram of concentrations of sodium, potassium, chloride 



and bicarbonate in human parotid saliva. 



(Thaysen, Thorn and Schwartz, 1954.) 



rate. In human parotid saliva the limiting level is normally about 

 60 mEq/1. and in the dog 40-50 mEq/1. (i.e. about twice the plasma 

 bicarbonate) (Thaysen, Thorn and Schwartz, 1954; Hildes and 

 Ferguson, 1955; Yoshimura, Takaoka and Mori, 1954; Sand, 

 1949; Wechsler, 1959). The cat sublingual saliva on the other hand 

 appears to be virtually free of bicarbonate. Lundberg (1957) found 

 this saliva to contain 156 mEq/1. sodium, 9 mEq/1. potassium and 

 151 mEq/1. chloride. Since calcium and magnesium together 

 amount to only 3-4 mEq/1. and phosphate to not more than 

 3 mEq/1., the bicarbonate must be less than 5 mEq/1. Kostlin and 

 Rauch's (1957) analysis of human sublingual saliva also suggests 

 a low bicarbonate concentration. Werther (1886) reported an 

 absence of "alkali" in sublingual saliva. Yoshimura et al (1959) 



P.S.G. 



