Imagine you are a potter trying to turn a lump of clay into a delicate, precise shape. What would you do first, and what would you do subsequently? Applied the same thinking to explain what happens to filtrate as it passes through the renal tubules.

Initially I would roughly shape the piece of clay without worrying about the details. Once I had the general shape I could then concentrate on fine tuning my pot. In the early part of the renal tubules we have bulk reabsorption occurring. This results in the reabsorption of most of the water and electrolytes that have been filtered, and normally all of the glucose and amino acids. This is occurring in the proximal convoluted tubule. As the filtrate passes further through the tubule system we can concentrate on fine tuning of reabsorption so that the requirements for homeostasis are met.