QS Study

Tubular Load

It is the amount of a substance incorporated into the filtrate by all the nephrons of both kidneys per minute. The total amount of a material that enters the tubular portion of the nephron each minute is said to be a tubular load. is the amount of a specific solute (electrolyte, glucose, or amino acid) dissolved in the fluid that enters Bowman’s capsule. There is an equation for this, but you have to know two things:

  • Plasma concentration of that solute – To determine this, draw blood, place in a spectrophotometer.
  • Patient’s GFR

If we want to know how much glucose was filtered into the nephron, we need to know that person’s blood plasma glucose levels, and we would need to calculate their Glomerular Filtration Rate (GFR). Each individual solute will have its own tubular load calculation.

The tubular load is expressed by TC.

TC = GFR x Plasma conc. of glucose

= 125 ml/min x 100 mg %

=125 ml/min x 1 mg/ml

= 125 mg/min

Again TC = Plasma load x filtration fraction.

So tubular load is the fraction of plasma load that is incorporated into the filtrate by all the nephrons of both kidneys each minute.

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