Three-Dimensional Reconstruction of Avian Medullary Cone and Lateral Relationships of Loops of Henle

Abstract

Although birds and mammals are the only vertebrates that can produce urine hyperosmotic to their plasma, the organization of the renal medulla of birds considerably differs from that of mammals. In this study, a three-dimensional model was generated from one cone in the renal medulla of a desert quail (Callipepla gambelii), and the spatial relationships between its limbs of loops of Henle and its collecting ducts were examined. Data on the spatial segregation of the collecting ducts and limbs of loops of Henle were collected. Collecting ducts formed a ring in the center, loops of Henle reaching deep into the medulla clustered within the ring, and loops ending superficially ended outside the ring. It was found that limbs of the same type did not cluster and that each loop’s pair of limbs remained near each other throughout the medullary cone. However, loops of Henle near the center of the cone, within the cluster of collecting ducts, tended to be longer than those outside. It is thought that this may have ramifications on the ability of the desert quail to concentrate its urine.