Medical devices and methods for controlling the flow of contents through an opening, such as an anastomosis formed during bariatric surgery. Generally, the medical device includes a tube and first and second radially extendable anchors attached to the tube. The anchors keep the medical device centered at the anastomosis or other opening, while the inner diameter of the tube restricts the passage of contents therethrough. A limiter may also be employed to vary the smallest diameter of the tube's lumen.