- Filtrate of varying osmolality
- Minimal Na+ and K+ reabsorption
- H2O reabsorption.
- Aldosterone: steroid hormone that acts to increase Na+ reabsorption. At the same time it enhances K+ and H+ secretion.
- Vasopressin (ADH):
- Brings aquaporins to the apical surface
- Makes collecting ducts permeable to water, otherwise water reabsorption is very low
- Urine of varying osmolality