ENTRY OF NEPHRONS INTO THE COLLECTING DUCT NETWORK OF THE AVIAN KIDNEY - A COMPARISON OF CHICKENS AND DESERT QUAIL

The avian kidney contains a population of nephrons with and without lo ops of Henle. How the collecting ducts of this heterogeneous populatio n of nephrons merge to exit as single ducts from the medullary cones h as been uncertain. The results of this study show that the collecting duct tree begins with the coalescence of the distal tubules of pairs o f loopless nephrons. These primary collecting ducts receive output fro m only loopless nephrons. Primary collecting ducts fuse in pairs and b ecome secondary collecting ducts. They receive the distal tubules of t ransition nephrons. Pairs of secondary collecting ducts fuse and becom e tertiary collecting ducts. Tertiary collecting ducts receive the dis tal tubules of looped nephrons. Thus, the fluid from all nephron types comingles as it passes through the medullary cone. The results of thi s study also show that the anatomical arrangement of medullary cones d oes not permit the output from one medullary cone to enter a second me dullary cone. Thus, all the medullary cones function as parallel units . This anatomical organization of the avian kidney affects its ability to produce a urine hyperosmotic to the plasma.