A catheter for connecting an administering device to an administering needle, the catheter including a catheter wall, a flow region limited by the catheter wall, and at least one catheter portion at which at least one partial piece of the catheter wall abuts at least one other partial piece of the catheter wall to releaseably block or obstruct the flow of a medium through the catheter, wherein the flow is unblocked or opened when the medium exhibits a pressure above a predetermined blocking pressure.