Renal Physiology — Flashcards

Flashcard 1: What is the formula for renal clearance ($C_x$)?

Answer: $C_x = \frac{U_x V}{P_x}$

Extra: $U_x$ = Urine concentration of X $P_x$ = Plasma concentration of X $V$ = Urine flow rate

Flashcard 2: What equation is used to calculate **free-water clearance** ($C_{H_2O}$)?

Answer: $$C_{H_2O} = V - C_{osm}$$ (where $V$ = urine flow rate; $C_{osm}$ = osmolar clearance)

Extra: Free-water clearance ($C_{H_2O}$) represents the volume of solute-free water that must be added to or removed from the urine to make it isotonic with plasma. - If **$C_{H_2O} = 0$**: Urine is isosthenuric (isosmotic to plasma). - If **$C_{H_2O} > 0$**: Free water is excreted (dilute urine; $U_{osm} < P_{osm}$). Seen in low ADH states (e.g., diabetes insipidus, water intoxication). - If **$C_{H_2O} < 0$**: Free water is reabsorbed (concentrated urine; $U_{osm} > P_{osm}$). Seen in high ADH states (e.g., SIADH, dehydration).

Flashcard 3: The fraction of filtered water reabsorbed may be measured using the equation: _____

Answer: 1 − 1 / (TF/P)inulin

Flashcard 4: Reabsorption of Na+ in the collecting duct creates a _____ luminal potential that facilitates K+ excretion

Answer: negative

Flashcard 5: The _____ limb (loop of Henle) is impermeable to Na+

Answer: thin descending

Flashcard 6: _____ is the volume of plasma completely cleared of a substance by the kidneys per unit time

Answer: Renal clearance

Flashcard 7: _____ syndrome is a renal tubular defect characterized by a defect in the thick ascending limb (of Henle) (location) of the nephron

Answer: Bartter

Flashcard 8: The _____ ratio is used as a marker for water reabsorption along the nephron

Answer: [TF/P]inulin

Flashcard 9: In the lumen of the early PCT, H2CO3 is converted into _____ and CO2 via the enzyme carbonic anhydrase IV

Answer: H2O

Flashcard 10: _____ is a hormone that inhibits Na+-phosphate cotransport in the proximal tubule

Answer: PTH