Stereological and electron microscopic study on the internal organization of the urinary secretory units in three species of birds

Abstract

Quantitative analysis of the kidney was undertaken in three species of bird: domestic fowl (Gallus domesticus), house sparrow (Passer domesticus) and domestic pigeon (Columba livia var. domestica). The volume and surface area of the renal components were measured. The fine structure of the proximal convoluted tubules showed intercellular spaces that were occupied by interdigitating folds at the basolateral membrane level. The distal tubules showed microvilli in the apical basement membrane into the tubular lumen. Microscopic study revealed that the domestic fowl had a greater volume of cortical tissue in the kidney compared with the other two species; this bird also had a greater medullary tissue volume than the other species. The volume and surface area of the renal corpuscles and proximal and distal convoluted tubules in the cortex were highest in the domestic fowl and lowest in the house sparrow. The volume and surface area of the proximal tubules, thin and thick limbs of the loop of Henle, and collecting ducts were lowest in the house sparrow, while the domestic pigeon had slightly higher values for these parameters. Blood capillaries in the domestic fowl had the greatest volume and surface area in the cortex and medulla. This study suggests that the volume and surface area in structural elements of the renal nephron in these birds play an important role in the concentration of urine.