Part 3 of the urinary lab. Walk the nephron, then put numbers on what it keeps and what it throws away.
Module B · Walk the nephron
Module C · Transport maximum
Filtered load = GFR × P
What the letters mean
- GFR
- — glomerular filtration rate: the volume of plasma filtered each minute. Here it is 125 mL/min, which is 1.25 dL/min.
- P
- — plasma concentration: how much of the substance is dissolved in the plasma (mg/dL or mEq/L). This is what the slider sets.
- Filtered load
- — the amount of the substance entering the tubule each minute.
- Tm
- — transport maximum: the most the tubule’s carriers can move each minute.
- Reabsorbed or secreted
- — the amount the carriers actually move each minute. It can never be more than Tm.
- Excreted
- — the amount leaving in the urine each minute: filtered load minus reabsorbed, or filtered load plus secreted.
Module D · Clearance
C = (U × V̇) ÷ P
What the letters mean
- C
- — clearance: the volume of plasma that is completely cleared of the substance each minute (mL/min).
- U
- — urine concentration: how much of the substance is dissolved in the urine.
- V̇
- — urine flow rate: the volume of urine made each minute. The dot means “per minute.”
- P
- — plasma concentration: how much of the substance is dissolved in the plasma.
- GFR
- — glomerular filtration rate: the volume of plasma filtered each minute, 125 mL/min.
Urine flow (V̇) is 1.0 mL/min for every row, and GFR is 125 mL/min. Work out each clearance, type it in, then check.
| Substance | P | U | Your C (mL/min) | C ÷ GFR | Verdict |
|---|