Which of the following is NOT an important function of the kidney?

Question

BlackTom AI · Accepted Answer

Kidneys conserve proteins; they do not excrete large amounts of albumen (albumin). This distinguishes normal renal function from pathological proteinuria.

1) Relevant knowledge points and concepts
- Major renal functions: filtration of blood, selective reabsorption, secretion, and excretion. Key roles include regulation of blood volume/pressure (via renin–angiotensin–aldosterone system and modulation of water reabsorption by ADH), reabsorption of electrolytes and nutrients (e.g., Ca2+), control of plasma ion concentrations (Na+, K+, Cl–) by tubular transporters and hormonal control, and maintenance of acid–base balance (bicarbonate reabsorption, H+ secretion).  
- Protein handling: the glomerular filtration barrier is size- and charge-selective; large negatively charged proteins such as albumin (≈66 kDa) are normally retained in plasma. Normal urinary protein excretion is <150 mg/day and albumin excretion is <30 mg/day (microalbuminuria 30–300 mg/day indicates disease).

2) Step-by-step reasoning
- Compare each option to known renal functions:
  a) Regulates blood volume and pressure — true: kidneys secrete renin, adjust Na+ and water reabsorption to alter blood volume and pressure.  
  b) Reabsorb important nutrients such as calcium — true: proximal and distal tubules reabsorb Ca2+, regulated by PTH and vitamin D.  
  c) Control plasma ion concentrations (Na+, K+, Cl–) — true: nephron segments and aldosterone/ADH precisely regulate these ions.  
  d) Regulate acid–base balance — true: kidneys reclaim HCO3– and excrete H+ to maintain pH.  
  e) Excretion of large amounts of albumen (protein) — NOT a normal function.

3) Intermediate/quantitative facts
- Albumin molecular weight ~66 kDa and carries negative charge; glomerular pores exclude most albumin. Normal albuminuria <30 mg/day; values much higher indicate glomerular damage.

4) Why the correct answer is correct
- Excreting large amounts of albumin is a sign of renal impairment (e.g., nephrotic syndrome), not a normal kidney role. The kidney’s barrier and reabsorptive mechanisms actively prevent significant albumin loss.

5) Why other options are incorrect choices
- The other four choices describe established, essential renal functions (blood pressure/volume regulation, nutrient and ion reabsorption/control, and acid–base balance).

6) Conclusion
- Therefore, the statement "Excretion of large amounts of albumen (protein)" is NOT an important (normal) function of the kidney, which matches the provided correct answer.

Which of the following is NOT an important function of the kidney?单项选择题

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