16(kidneys) Flashcards
(9 cards)
Define renal plasma flow (RPF) and how it differs from GFR.
RPF is the volume of plasma delivered to the kidneys per unit time. GFR is the volume of plasma filtered by glomeruli per unit time. Approximately 20% of RPF is filtered, so GFR ≈ 0.2 × RPF.
What marker (exogenous or endogenous) is used to measure RPF, and how?
Para-aminohippuric acid (PAH) clearance approximates RPF because PAH is freely filtered and actively secreted by proximal tubule cells, so nearly all PAH entering the kidney is excreted. RPF ≈ PAH clearance.
How does sympathetic nervous system activation affect renal function during acute hemorrhage?
Sympathetic activation constricts afferent arterioles (via α₁-adrenergic receptors), reducing RPF and GFR to conserve blood volume. It also stimulates renin release, activating RAAS to retain Na⁺ and water.
What is renal autoregulation, and why is it clinically important?
Renal autoregulation maintains relatively constant renal blood flow and GFR over a range of mean arterial pressures (≈80–180 mm Hg) via myogenic and tubuloglomerular feedback mechanisms. It protects glomeruli from pressure fluctuations.
How is phosphate homeostasis influenced by the kidney?
The proximal tubule reabsorbs filtered phosphate via sodium–phosphate cotransporters. Parathyroid hormone inhibits phosphate reabsorption, increasing phosphate excretion, thereby balancing plasma phosphate levels.
What changes in renal handling of calcium occur under PTH influence?
PTH increases distal tubule calcium reabsorption while reducing phosphate reabsorption in the proximal tubule. It also stimulates 1α-hydroxylase to increase calcitriol production, enhancing intestinal Ca²⁺ absorption.
Why is urine osmolality an important clinical measurement?
Urine osmolality reflects the kidney’s ability to concentrate or dilute urine. High osmolality indicates water conservation (e.g., dehydration or high ADH), and low osmolality indicates water excretion (e.g., overhydration or low ADH).
What is the significance of the clearance equation?
This equation calculates the volume of plasma from which substance S is completely cleared per unit time. For inulin or creatinine, it approximates GFR; for PAH, it approximates RPF.
How does diabetic nephropathy initially affect GFR, and what is the long-term consequence?
Early diabetic nephropathy causes hyperfiltration (increased GFR) due to glomerular hypertension. Over time, damage to glomeruli and basement membranes leads to declining GFR and progressive kidney failure.
