Cell culture apparatus for emulating gastrointestinal tract conditions and comprising at least two adjacent, microfluidic, cell cultivation channels separated by a permeable or semipermeable membrane, a first channel carrying gastrointestinal tract epithelial cells or tissues and a second channel carrying luminal and preferably mucosal microbiota, and wherein said second channel comprises one or more dwell chambers capable of providing a location for unattached luminal flora to reside away from any direct flow in said second channel, permits modelling of multiple sections of the gastrointestinal tract and control of retention times.