Morphometry and residual strain in porcine ureter.

Recent studies on blood vessels, the heart, trachea and esophagus have shown that these organs in the zero-stress state are not closed circular cross-sections of rings, but open sectors. Any analysis of stress and strain must begin with organs in the zero-stress state. This report presents data on morphometry of the zero-stress and no-load states of the porcine ureter, and on residual strains and opening angles. The zero-stress state of the ureter is demonstrated by cutting the ureter into rings and cutting the rings into sectors; each sector is characterized by an opening angle. The outer and inner circumferences, the cross-sectional area of the ureteral wall and the number of buckles showed axial variation, with the highest values proximally in the ureter. Residual strain in the circumferential direction was significant, but showed no axial variation. The opening angles were approximately 30 degrees at the most distal and proximal sites and approximately 90 degrees in mid-ureter. The opening angle showed positive correlation to the wall thickness in the zero-stress state, residual strain at the outer circumference and negative correlation to the length of the outer circumference in the zero-stress state. Residual strains must be taken into account when studying physiological problems in which the stresses and strains are important, e.g. the urine transport function of the ureter.