Gastrointestinal (gi) tract: contributes to and is impacted by all the previous systems; therefore is incredibly important. Receives 1/3 of the total cardiac output. Produces acids and bases, so it contributes to overall body ph. Receives major nerves (i. e. vagus); also has its own nervous system, called the enteric nervous. Produces some biologically active hormones system: performs 3 or 4 things. In the neonate, the salivary glands are important; important for creating a connection between the mouth and the mother"s nipple: provide lubrication in oral cavity for moist mouth. Pump is not regulated; pump is on basolateral side, so there must be channels for facilitated diffusion on the apical sides. Sns (dry, gummy mouth) produces secretions of organic ions: pns >> sns in terms of volume secretion (about 10:1, hco3. (important in saliva as a buffer) secreted into lumen of striated duct by an active transport system (specific hco3. Atpase); not significant secretion at rest, but increases due to both.