This paper presents a new modelling technique for the defor- mation of thin anatomical structures like membranes and hollow organs. We show that the behaviour of this type of surface tissue can be ab- stracted with a modelling of their elastic resistance using shell theory. In order to apply the shell theory in the context of medical simulation, our method propose to base the geometrical reconstruction of the organ on the shape functions of the shell element. Moreover, we also use these continuous shape functions to handle the contacts and the interactions with other types of deformable tissues. The technique is illustrated using several examples including the simulation of an angioplasty procedure.