Question

Explain the relationship between transport maximum, renal threshold, and urine concentration of glucose.

Answer 1

Transport maximum

The transport system in the renal tubule like transport systems in the other part of the body have their maximal rate,which is called as the Transport Maximum.(Tm)

• This is the rate at which the tubule maxillary transports a particular solute.That means the amount of particular solute transported depends on the amount of the solute in the tubular fluid present up to the Tm for the solute.
• Tm is the amount of substance delivered to the tubule per minute.
• When the concemtration of the solute in tubular fluid is more than the Tm concentration,the mechanism of transport is said to be saturated.

Renal Threshold

This is the concentration of solute in the plasma at or above which the solute first appears in urine or appears in more amount than its normal concentration.

Urine concentration of glucose in relation to renal threshold and transport maximum :-

1. The rate of reabsorption of glucose is proportional to the amount of glucose filtered.Therefore plasma glucose levels determines the transport maximum for glucose (Tmg)
2. When a graph of Tmg is plotted,the actual curves deviates from the ideal curve.This deviation is called renal splay. It is due to - Tmg is not same in all the tubules. and - Amount of glucose removed from each tubule is not complete even when the amount filtered is below the tmg.