An implantable digestive organ is provided for the transport of materials through the digestive tract and in one particular application to an artificial large bowel for replacing all or part of a colon. The prosthetic organ of one embodiment includes an outer support structure, an expandable member or members located within the support structure, and a flexible inner member forming a conduit for passage of material. The inner member is located within the outer member and the expandable member(s) is located between the inner member and the support structure. The expandable members are expanded and contracted, or inflated and deflated to provide pumping action that pumps material through the organ. The prosthesis may also include valves or sphincters at its entrance and/or exit points where material moves into and out of the prosthesis. An implantable pump may be included for inflating and deflating the expandable members in a desired sequence.