75-76: TFP Clearance I & II Flashcards
[tubular fluid solute] compared to [plasma solute] is a function of concentration and amount of solutes in tubular
fluid
TF/P
What is TF/P dependent upon?
H2O reabsorption along nephron
TF/P formula
C = Q/V
If more H2O reabsorbed than
solutes or secretion of solute then what is TF/P?
Greater than 1
If more solute reabsorbed than H2O then what is TF/P?
Less than 1
What is volume of plasma cleared of a particular solute by the kidneys per unit time?
Renal Clearance
Renal Clearance formula
C = [U]x X V / [P]x
Filtered Load formula
GFR x [P]x
Excretion Rate formula
V x [U]x
How is glucose transported from tubular lumen into cell?
Na+/Glucose Cotransporter
How is glucose transported from cell into capillary?
Facilitated diffusion
What is the plasma glucose concentration threshold?
2 mg/mL or (200 mg/dL)
What is the maximum transport of glucose?
350-375 mg/min
______ clearance can be used as a measure of GFR because its neither absorbed or secreted
Inulin
Clinically, what is used to measure GFR instead of Inulin?
Creatinine: (overestimates GFR)
Blood Urea Nitrogen: (underestimates GFR)
What are the problems of using Inulin clinically?
Must be infused intravenously
Continual blood sampling required
Chemical analysis cumbersome
What are the benefits of using Creatinine instead of Inulin, clinically?
Endogenous (by-product of muscle metabolism)
Released into blood at relatively constant rate (only need one blood sample)
REABSORPTION OR
SECRETION RATE = _______ minus ______
Filtered Load minus Excretion Rate
______ clearance can be used as an estimate of RPF** because its freely filterable
PAH (Para-Amino-Hippurate)
**(only IF plasma conc. of PAH is less than renal threshold conc.)
What is the threshold of unbound PAH plasma concentration?
0.15 mg/mL or (15 mg/dL)
What occurs when the unbound PAH plasma concentration is greater than 15 mg/dL?
PAH secreted or excreted
What occurs when the unbound PAH plasma concentration is less than 15 mg/dL?
PAH remains in the blood
What occurs when the glucose plasma concentration is greater than 200 mg/dL?
Glucose transporters will be oversaturated and glucose will end up in urine
Clearance ratio formula
CR = Cx / Cinulin
Cx : clearance of substance
Cinulin: clearance of inulin
Cx / Cinulin < 1.0
Clearance of Reabsorbed Solutes
Cx / Cinulin > 1.0
Clearance of Secreted Solutes
Measures Na+ excreted in urine relative to amount reabsorbed by kidney
Fractional Excretion of Sodium
What is the clinical use of Fractional Excretion of Sodium?
Part of evaluation of acute renal failure and oliguria
Low fractional excretion of Sodium (<1%)
Na+ retention by kidney (pre-renal disease)
High fractional excretion of Sodium (>1%)
Na+ wasting due to tubular damage/intrinsic renal failure (acute tubular necrosis)
Osmolar Clearance formula
Cosm = (Uosm x V) / Posm**
**IF Posm is constant (300 mOsm/L)
Free water
Solute-free water
Method for assessing the ability of kidney to dilute/concentrate urine
Free water clearance
Free water clearance formula
CH20= Vā(Uosm x V) / Posm
CH20= 0 when?
when no solute-free water is excreted
isotonic urine
CH20 is +ve when?
when ADH levels are low, solute-free water is excreted
hypotonic urine
CH20 is -ve when?
when ADH levels are high; all solute-free water is reabsorbed
hypertonic urine
