Urine - physiological and pathological components.

Introduction

Urine is a liquid waste product excreted by the kidneys through the urinary tract. It reflects the metabolic and functional status of the body and plays an essential role in maintaining fluid, electrolyte, and acid-base balance. The composition of urine includes both physiological (normal) and pathological (abnormal) components, which can be assessed diagnostically.

Physiological Components of Urine

Normal urine is a clear, straw-colored fluid with a specific gravity of 1.005–1.030 and pH ranging from 4.5 to 8.

Main physiological components:

- Water: ~95% of urine.

- Urea: Major nitrogenous waste, product of protein metabolism.

- Creatinine: From muscle metabolism.

- Uric acid: Product of purine metabolism.

- Electrolytes: Sodium, potassium, chloride, calcium, phosphate, magnesium.

- Small amounts of amino acids, vitamins, and hormones.

- Organic acids: Such as hippuric acid, citric acid.

Pathological Components of Urine

Pathological components are substances that are not normally present in significant amounts and may indicate disease:

- Glucose (glucosuria): Seen in diabetes mellitus.

- Protein (proteinuria): Indicates renal damage, nephrotic syndrome.

- Ketone bodies: Appear in uncontrolled diabetes, starvation.

- Hemoglobin/myoglobin: Hematuria, rhabdomyolysis.

- Bilirubin and urobilinogen: Liver disease.

- White blood cells (pyuria): Urinary tract infection.

- Casts and crystals: Indicate renal pathology or metabolic disorders.

Microscopic examination and chemical analysis of urine help in the diagnosis of metabolic, renal, and systemic diseases.

Conclusion

Urine analysis is a fundamental diagnostic tool in clinical medicine. It provides critical insights into kidney function and systemic health. Distinguishing between physiological and pathological components is essential for identifying and managing various medical conditions.

References

1. Guyton and Hall Textbook of Medical Physiology, 14th Edition

2. Lippincott Illustrated Reviews: Biochemistry, 7th Edition

3. Lehninger Principles of Biochemistry, 7th Edition