What is the major function of the renal system?

• A. To filter blood and produce urine, maintaining fluid and electrolyte balance
• B. To regulate body temperature
• C. To transport oxygen
• D. To store hormones

Answer: (A)

The kidneys’ main job is to filter waste from the blood and produce urine, which helps keep fluid levels and electrolyte balance within tight limits. This happens through the nephron’s steps: glomerular filtration forms a filtrate from the blood, then the tubules reabsorb water and essential ions while secreting wastes into the filtrate. By adjusting how much water and which ions are excreted, the kidneys maintain proper fluid volume, electrolyte concentrations, and acid-base balance, and they influence blood pressure via hormonal regulation. They also contribute to other important functions, like producing erythropoietin to support red blood cell production and activating vitamin D for bone health. The other options aren’t the kidneys’ primary roles—temperature regulation is mainly a function of the skin, oxygen transport is done by the lungs and circulatory system, and storing hormones isn’t a primary renal duty.