Substance Absent in Normal Urine
Which substance is NOT found in normal urine?
- Glucose — Correct Answer
- NaCl
- Creatinine
- Urea
Correct Answer: Glucose
Glucose is NOT found in normal urine. Glucose is completely reabsorbed in the PCT (Proximal Convoluted Tubule) under normal blood glucose levels.
Normal Urine Composition
Normal urine contains: Water (95%), Urea, Creatinine, Uric acid, Sodium (NaCl), Potassium, Phosphates, Sulfates, Ammonium salts, urobilin (gives yellow colour)
Why Glucose Is Absent in Normal Urine
The renal threshold for glucose is approximately 180 mg/dl. When blood glucose is below this level, all filtered glucose is reabsorbed by Na⁺-glucose cotransporters (SGLT) in the PCT. Only when blood glucose exceeds 180 mg/dl (as in diabetes mellitus) does glucose appear in urine (glycosuria).
Why Other Options ARE Found in Normal Urine
- NaCl: Excess sodium and chloride are excreted — regulated by aldosterone
- Creatinine: A nitrogenous byproduct of muscle metabolism; freely filtered and not reabsorbed — always present in urine; used to measure GFR
- Urea: Principal nitrogenous waste of mammals; NH₃ is converted to urea in liver (urea cycle) → excreted in urine
Contrast: Avian Urine
The principal nitrogenous component of avian urine is uric acid (not urea), as birds convert NH₃ to uric acid in liver and kidney.
📚 About this Topic — Animal Physiology
This multiple choice question is from Animal Physiology, Animal Refresher. It has 4 options with a detailed explanation of the correct answer. Practice more MCQs from Animal Physiology to strengthen your preparation.
