Histomorphometry and strain distribution in pig duodenum with reference to zero-stress state.

The morphometry at no-load and zero-stress states and residual circumferential strains were determined along the pig duodenum in vitro in seven pigs. The no-load state was obtained by cutting eleven 2-mm-wide rings at 10% intervals along the duodenum. The zero-stress state was obtained by cutting the rings radially. The zero-stress state provides a standard morphological state to describe tissue since internal and external forces do not affect the tissue. The morphometric measures were obtained from digitized images, and the layer thicknesses were measured from histological sections. The mucosal and serosal circumferences, the wall thickness, and the wall thickness-to-mucosal radius ratio were largest in the proximal end of the duodenum (f > 1.9, P < 0.05). The thickness of the submucosal stratum compactum layer and the opening angle increased in distal direction (f = 2.3, P < 0.05 and = 6.5, P < 0.001). The residual strain at the mucosal surface was negative, indicating that the mucosa-submucosa layers of duodenum in no-load state are in compression. Distension experiments showed that the residual strain makes the stress distribution through the wall more uniform in the pressurized state. In conclusion, the large circumferential residual strains must be taken into account in the study of physiological problems, in which the stresses and strains are important, eg, the bolus transport function.