The document discusses transport maximum limits for actively transported substances like glucose in the kidney. It notes that glucose has a transport maximum of around 375 mg/min in humans. When glucose delivery to the tubule exceeds this rate, the excess is not reabsorbed and passes into the urine instead. In contrast, passively transported substances do not have a transport maximum. The document also outlines the mechanisms of sodium, chloride, water and urea transport and reabsorption at different points along the nephron.