AIM:Residual stress and strain are important forgastrointestinal function and relate to the geometric“configuration,the loading conditions and the zero-stressstate of the gastrointestinal tract.The purpose of thisproject is to provide morphometric data and residual strainsfor the rat small intestine(n=11).METHODS:To approach the no-load state,the intestine wassurgically excised,transferred to an organ bath and cuttransversely into short ring-shaped segments.Each ringwas cut radially for obtaining the zero-stress state.Theresidual stress can be characterised by an opening angle.The strain difference between the zero-stress state and theno-load state is called residual strain.RESULTS:Large morphometric variations were found along thesmall intestine.The wall thickness was highest in the proximalduodenum and decreased in distal direction along the axis ofthe small intestine(P<0.001).The circumferential length ofthe inner and outer surfaces decreased rapidly along the lengthof duodenum by 30-50 %(P<0.001).The wall area and lumenarea showed a similar pattem(P<0.001).In zero-stress statethe rings always opened up after making the cut.Theexperiments resulted in larger inner circumferential length andsmaller outer circumferential length when compared to the no-load state.The wall thickness and wall area did not differbetween the no-load and zero-stress state.The opening angleand tangent rotation angle increased along the length of theduodenum and had its highest value 30% down the intestine.Further down the intestine it decreased again(P<0.001).Theserosal residual strain was tensile with the highest value closeto the ligament of Treitz(P<0.001).The mucosal residualstrain was compressive in all segments of the small intestinewith average values between-0.25 and-0.4 and with the lowestvalues close to the ligament of Treitz(P<0.001).CONCLUSION: Axial variation in morphometric properties and residual strains were found in the small intestine. Existence of large residual strains indicates that the zero stress state must be considered in future biomechanical studies in the gastrointestinal tract. AIM: Residual stress and strain are important for gastrointestinal function and relate to the geometric ”configuration, the loading conditions and the zero-stress state of the gastrointestinal tract. The purpose of thisproject is to provide morphometric data and residual for the rat small intestine (n = 11) .METHODS: To approach the no-load state, the intestine wassurgically excised, transferred to an organ bath and cuttransversely into short ring-shaped segments. Each ringwas cut radially for obtaining the zero-stress state. The residual stress can be characterized by an opening angle. The strain difference was the zero-stress state and then-load state is called residual strain. RESULTS: Large morphometric variations were found along thesmall intestine. The wall thickness was highest in the proximalduodenum and decreased in distal direction along the axis of the small intestine (P <0.001). The circumferential length of the inner and outer surfaces was rapidly along the length of duodenum by 30-50% (P <0.001) .The wall area and lumenarea showed a similar pattem (P <0.001) .In zero-stress statethe rings always opened up after making the cut.Theexperiments resulted in larger inner circumferential lengthandsmaller outer circumferential length when compared to the no-load state. The wall thickness and wall area did not differ between the no-load and zero-stress state. The opening angle and tangent rotation increased by the length of theduodenum and had its highest value 30% down the intestine .Further down the intestine it decreased again (P <0.001) .Theserosal residual strain was tensile with the highest value closeto the ligament of Treitz (P <0.001) .The mucosal residualstrain was compressive in all segments of the small intestinewith average values ​​between- 0.25 and-0.4 and with the lowestvalues ​​close to the ligament of Treitz (P <0.001) .CONCLUSION: Axial variation in morphometric properties and residual were found in the small intestine. Existence of large residual strains indicates that the zero stress state must be considered in future biomechanical studies in the gastrointestinal tract.