Water bicarbonate and

Carbonic acid is the most abundant acid in natural water systems and is the acid most responsible for rock weathering. Bicarbonate ion is generally the dominant anion in fresh surface- and ground-waters. Bicarbonate and carbonate ions are also the chief contributors to total alkalinity in natural waters (see below). For such reasons we will consider carbonate-solution chemistry in some detail. 

The intestinal mucosa secretes an alkaline, watery juice containing several enzymes. This secretion mixes with pancreatic juice and bile to form the intestinal juice. The succus entericus, a pure intestinal secretion, is a thin liquid consisting of water, bicarbonate, and a few enzymes. Among the enzymes found in the intestinal secretion are exopeptidase, aminopeptidase, amylase, maltase, invertase, lactase, lipase, and entero-kinase, which activates trypsinogen. 

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