QS Study

Transport maximum (Tm) is the maximum and constant rate at which every actively reabsorbed or secreted substance, are transported by the tubular system of both kidneys per minute. It refers to the point at which increases in the concentration of a substance do not result in an increase in movement of a substance across a cell membrane.


Tm of glucose = 300 mg/min in case of female and 350 mg/min in case of the male.

Fig: Transport maximum

Transport maximum for glucose is expressed by the maximum transporting capacity of the SGLT transportation system. Excessive glucose is not reabsorbed and consequently passes into the urine. Transport maximum for glucose tubular transport system in adult humans is about 375 mg/min.

Tm of glucose 350 mg/ min means that 350 mg glucose is reabsorbed its maximum rate through the tubules in each minute. If the rate is above this value then glucose is excreted out through urine.