Which statement accurately summarizes glomerular filtration rate (GFR) regulation short-term and long-term?

• A. GFR is the rate of filtrate formation; short-term regulation via autoregulation of afferent/efferent arterioles; long-term via hormonal and neural influences (RAAS, sympathetic input).
• B. GFR is the rate of urine formation; short-term regulation via hydration; long-term via diet.
• C. GFR is the total plasma volume filtered per hour; regulated by liver hormones.
• D. GFR is the rate of chylomicron production.

Answer: (A)

GFR is the rate at which filtrate is formed in the kidney’s glomeruli. Short-term control comes from intrinsic autoregulation that adjusts the tone of the afferent and efferent arterioles, helping keep filtration steady despite blood pressure swings. Long-term adjustments involve extrinsic influences from hormones and neural input, notably the renin-angiotensin-aldosterone system and sympathetic signals, which modulate renal blood flow and filtration over hours to days. This combination is precisely what the correct statement describes: GFR as filtrate formation, with short-term autoregulation of the arterioles and long-term regulation by hormonal and neural influences. The other options misdefine GFR (not urine formation, not a rate of plasma volume filtered per hour, and not related to chylomicron production or liver hormones).