6 - Renal Handling of Fluids and Electrolytes Flashcards
How do you calculate urine flow rate?
Urine flow rate (UF) = (urine volume) / (time of collection)
What is renal clearance? How do you calculate it?
Renal clearance of a substance is the volume of plasma that is completely cleared of the substance by the kidneys per unit time.
Cx = (Ux) x (UF) / Px
Renal clearance = Urine concentration of X x Urine flow rate / plasma concentration of X
What is osmolar clearance and how do you calculate it?
The clearance of all osmotic substances.
Cosm = (Uosm x V) / Posm
Osmolar clearance = Urine osmolarity x urine flow rate / plasma osmolarity
What is free water clearance and how do you calculate it?
CH20 is the rate at which solute-free water is excreted by the kidneys.
CH20 = UF - Cosm
Free water clearance = urine flow rate - osmolar clearance
How do you calculate renal excretion of a substance?
Excretion rate of substance X = Urine concentration of X x Urine flow rate
What is fractional excretion of sodium? What is it an index of?
The percentage of sodium filtred by the kidney which is excreted in the urine.
It’s an index of renal tubular reabsorption of sodium.
How do you calculate fractional excretion of sodium?
FENa = (UNa x UF) / (PNa x GFR)
Fractional excretion of sodium = (Urinary concentration of sodium x urine flow rate) / (Plasma concentration of sodium x GFR)
Adding a hypertonic solution to the systemic circulation will have what effect on intracellular fluid volume?
It will decrease.
As the tubular fluid moves from he beginning to the end of the proximal tubule, what happens to the creatinine concentration?
It increases - it’s not absorbed, but NaCL and water is so the concentration increases.
What mechanisms contribute to the autoregulation of glomerular filtration rate?
Tubularglomerular feedback and myogenic response are the main controllers of autoregulation of GFR.
What effect does the stimulation of renal sympathetic nerves have?
Increased sympathetic nerve activity means we are losing blood/decrease in BP and the sympathetic activity is to compensate.
Therefore, we want to retain sodium and water via an increase in renin release.
GFR would decrease due to the restriction in BVs.
