The valva portalis renalis in the duck (Anas platyrhynchos)

The morphology of the valva portalis renalis of the duck was investigated, using histological, SEM and TEM techniques. The wall thickness of the vena iliaca externa, the vena portalis renalis caudalis, the vena iliaca communis and the vena renalis caudalis was morphometrically evaluated. The blood pressure in these veins was measured using a three-way H2O manometer. The valva portalis renalis was composed primarily of epithelioid cells and lined with endothelium. Throughout the entire valva there was a dense complex of nerve structures made up of fibers and fiber bundles which also extended beneath the endothelium of the valva and around the subendothelial epithelioid cells. The wall thicknesses of the veins supplying the renal portal system (vena iliaca externa and vena portalis renalis caudalis) were greater than those of the vessels collecting the renal refluent venous blood (vena iliaca communis and vena renalis caudalis). In addition, the blood pressure values taken in the vena iliaca externa and the vena portalis renalis caudalis were much higher than those in the vena iliaca communis and the vena renalis caudalis. The above observations suggest that the renal portal system works at higher blood pressure levels than the general venous system and that the valva portalis renalis regulates its aperture in order to maintain a constant blood pressure and a continuous blood flow in the renal portal system vessels, hence avoiding damage to the renal parenchyma caused by pressure overloads.