A device for accessing tissue within a body lumen, comprising: an elongated body portion defining a lumen； an anchoring mechanism including an expanding structure on a distal portion of the elongated body portion, the expanding structure including a plurality of longitudinally spanning retractable ribs, the expanding structure moving from a fully-retracted configuration in which the each of the plurality of ribs is constricted and substantially parallel to the elongated body to an operative configuration in a body in which at least a portion of each of the plurality of ribs extends away from the device without altering a length of the anchoring mechanism； and a control mechanism selectively engaging the anchoring mechanism, wherein the control mechanism is configured to move the anchoring mechanism between the fully-retracted configuration and the operative configuration.
