Composition of secretions into the gastrointestinal tract

**Table 2:** Summary of concentrations of major anions and cations in gastrointestinal fluids. Saliva differs from plasma in being more dilute and having a high concentration of potassium. Stomach content is similar to plasma except that the Na $\ensuremath{^+}$ content is lower (presumably being replaced by protons). Pancreatic secretion differs mainly with respect to a high concentration of HCO $\ensuremath {_3^-}$ with the other anion Cl $\ensuremath{^-}$ being reduced to ensure that the total anions equate with the total cations. Bile is remarkable similar to plasma apart from a slight increase in HCO $\ensuremath {_3^-}$ .
	Plasma	Saliva	Stomach	Pancreas	Bile
Na $\ensuremath{^+}$	140	10	60	140	145
K $\ensuremath{^+}$	4	26	10	5	5
Cl $\ensuremath{^-}$	110	10	130	75	100
HCO $\ensuremath {_3^-}$	30	30	0	115	35

The normal concentrations of the major cations (Na $\ensuremath{^+}$ , K $\ensuremath{^+}$ ) and the major anions (Cl $\ensuremath{^-}$ , HCO $\ensuremath {_3^-}$ ) in gastrointestinal secretions are summarised in table 2. As shown in the table each fluid should be compared to plasma.

Saliva differs from plasma in that it is quite dilute and has a high K $\ensuremath{^+}$ concentration.

Gastric juice is similar to plasma except that the Na $\ensuremath{^+}$ content is reduced so that protons may be secreted. In addition there is no HCO $\ensuremath {_3^-}$ .

Pancreatic juice differs from plasma in having a large HCO $\ensuremath {_3^-}$ concentration. Due to the high HCO $\ensuremath {_3^-}$ the other anion Cl $\ensuremath{^-}$ is reduced so that the total count of the anions approximates that of the cations.

Bile is similar to plasma except that there is a slightly higher HCO $\ensuremath {_3^-}$ concentration.