The glomerular filtration rate of the human kidney may be determined by measuring the plasma clearance of:
First, I remember that GFR is a key indicator of kidney function. The gold standard for measuring GFR is the clearance of a substance that is freely filtered by the glomerulus and neither reabsorbed nor secreted by the renal tubules. Inulin is the classic example because it meets these criteria. However, in clinical practice, creatinine is more commonly used, although it's not perfect because some creatinine is secreted by the tubules.
Wait, but the question might be looking for the ideal substance. Inulin is the gold standard, but in real life, creatinine is used. However, sometimes other substances like urea or glucose might be mentioned as distractors. Let me think. Urea is both filtered and reabsorbed, so it's not accurate. Glucose is reabsorbed completely, so its clearance is zero. So if the options included inulin, creatinine, urea, and glucose, the correct answer would be inulin for the theoretical question and creatinine for the practical one.
But the correct answer given here is probably inulin. Let me check. The question says "may be determined by measuring the plasma clearance of..." So the gold standard is inulin, hence the correct answer would be inulin. The options might be inulin, creatinine, urea, and something else. The wrong options would be those substances that are not freely filtered or are reabsorbed/secreted.
So, for the explanation: the core concept is that GFR is measured by a substance that's freely filtered and not reabsorbed or secreted. Inulin is the ideal, creatinine is used clinically. The correct answer is inulin. The other options like urea (reabsorbed), glucose (reabsorbed), and creatinine (some secretion) are incorrect. The clinical pearl is that while inulin is the gold standard, creatinine is more practical but has limitations.
**Core Concept**
Glomerular filtration rate (GFR) is measured using a substance that is freely filtered by the glomerulus and neither reabsorbed nor secreted by the renal tubules. **Inulin** is the gold standard for this measurement, as it meets these criteria. Creatinine is clinically used despite partial tubular secretion, while urea and glucose are inaccurate due to reabsorption or secretion.
**Why the Correct Answer is Right**
**Inulin** is a polysaccharide that is freely filtered by the glomerulus but not reabsorbed, secreted, or metabolized by the kidneys. Its clearance directly reflects GFR because the amount excreted in urine equals the filtered load. This makes it the **ideal marker** for GFR estimation in experimental settings, though it is not used clinically due to the need for intravenous administration.
**Why Each Wrong Option is Incorrect**
**Option A: Creatinine** – Creatinine is commonly used clinically but is partially secreted by the tubules, leading to overestimation of GFR.
**Option B: Urea** – Urea is reabsor