Final answer:
The transport maximum is the limit of substance reabsorption in the nephron's PCT, with excess levels potentially indicating diabetes.
Step-by-step explanation:
The transport maximum is the maximum amount of a substance that can be reabsorbed (or secreted) across the tubule epithelium in a given period of time. For example, in the proximal convoluted tubule (PCT) of the nephron, almost 100% of glucose and amino acids are typically reabsorbed. However, if blood glucose levels exceed the transport maximum, glucose may appear in urine, indicating a potential diabetes mellitus condition. The transport maximum varies between individuals, with approximate values of 375 mg/min for males and 300 mg/min for females being related to glucose reabsorption.