[The remarkable accomplishments of the kidney--from molecular mechanisms to organ function]

The kidneys control chemical composition and volume of the extracellular fluid. Total extracellular volume passes about 10 times per day through the kidneys. Only 1% is excreted including metabolic waste products and excess intake by nutrition. While the proximal tubules are adapted to mass transport, the distal tublar cells are specialized to selectively retain or reject water and electrolytes, controlled by exrenal hormonal factors. For these purposes an optimal adjustment of morphologic, encymatic, physico-chemical and molecular features has developed in the course of evolution. With modern experimental techniques it is possible to demonstrate the mode of operation of single protein molecules in the cell membranes as sites of active or passive transport processes. This enables us to describe the basic mechanism of kidney function and to better understand the sequence of events leading to pathological disturbances of this organ.