Final answer:
Glucose is not normally found in urine; its presence can indicate a condition like diabetes mellitus.
Step-by-step explanation:
The substance not found in normal urine is glucose. Urine typically contains urea, uric acid, sodium, and H+ ions, which are by-products of normal metabolism and are excreted by the kidneys. However, glucose is reabsorbed by the nephron and is not usually present in urine unless the blood glucose levels are abnormally high, such as in the case of uncontrolled diabetes mellitus.
Normal urine composition reflects the body's need to retain important substances like glucose while eliminating waste products. In normal urine, glucose is not found. Glucose is typically reabsorbed by the nephron to maintain homeostatic plasma concentrations. If glucose is present in urine, it may indicate a medical condition such as diabetes.