Collecting Tubules and Ducts:

1. Structure. These differ from the nephrons in their embryonic origin and can be easily distinguished from the proximal and distal tubules in sections. Their block like lining cells have distinct intercellular borders; they are cuboidal in the smaller tubules and columnar in the larger leg, papillary) ducts of the medulla. Since their cytoplasm stains poorly, the cells appear clear or white.

2. Function. The cortical collecting tubules receive a reduced volume of hypotonic or isotonic urine from the nephrons and empty it into larger collecting ducts. These leave the cortex in medullary rays and enter the medulla, increasing in size until they open into a minor calyx through the tips of papillae.