Life and Medical Sciences
Cell & Developmental Biology
Wiley InterScience Backfile Collection 1832-2000
The avian kidney is composed of cortical and medullary lobules, with the former surrounding branches of the renal vein. Cortical lobule diameters varied intraspecifically according to level of association with the venous system, and interspecifically were greatest in nonpasserines. All cortical tissue examined contained maculae densae.Each medullary lobule receives collecting ducts and loops of Henle from several cortical lobules. Such a complex may be viewed as a lobe, and the entire kidney as multilobar. The relative diameter of a medullary lobule appears directly related to the number of cortical units with which it is associated. Distally, most lobules vary from 0.3 to 0.5 mm in diameter, and contain 20 to 30 collecting ducts. The latter fuse dendritically as they traverse a medullary unit, and eventually form ureteral branches which drain directly into the ureter.Intramedullary organization in passerines involves aggregated thin limbs bounded by collecting ducts which in turn are surrounded by uneven layers of thick limbs. While some nonpasserines approach this pattern, others lack apparent organization of intramedullary elements. The turn of Henle's loop was restricted to the thick limb in all birds examined. Avian and mammalian thick limbs are similar in diameter, but avian thin limbs are typically wider.Small kidneys have short ureteral branches with primary stems clustered in each kidney division. In larger kidneys, where medullary lobules are often remote from the ureter, ureteral branches are long and not clustered.
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