Tubular Reabsorption and Secretion — Flashcards

Flashcard 1: In the _____ limb (loop of Henle), osmolarity of the tubular fluid decreases

Answer: thick ascending

Flashcard 2: The _____ cells of the late distal tubule and collecting duct reabsorb K+

Answer: alpha-intercalated

Flashcard 3: Glucose in the cells of the PCT enter the peritubular capillary blood through _____ and GLUT2 transporters

Answer: GLUT1

Flashcard 4: Loop of henle is a countercurrent _____ and vasa recta is a countercurrent _____ in maintainence of osmolality gradient

Answer: multiplier; exchanger

Flashcard 5: HCO3- is transported across the basolateral membrane into the blood by:\n1. Proximal tubule: _____\n2. Alpha-intercalated cells: Cl--HCO3- exchange

Answer: Na+-HCO3- cotransport

Flashcard 6: The _____ cells of the late distal tubule and collecting duct reabsorb Na+ and H2O

Answer: principal

Flashcard 7: Glucose is reabsorbed in the _____ by Na+/glucose (SGLT) cotransporters

Answer: early PCT

Flashcard 8: 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 9: 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 10: The fraction of filtered water reabsorbed may be measured using the equation: _____

Answer: 1 − 1 / (TF/P)inulin